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Myzus persicae (green peach aphid) salivary components induce defence responses in Arabidopsis thaliana
Abstract
Myzus persicae (green peach aphid) feeding on Arabidopsis thaliana induces a defence response, quantified as reduced aphid progeny production, in infested leaves but not in other parts of the plant. Similarly, infiltration of aphid saliva into Arabidopsis leaves causes only a local increase in aphid resistance. Further characterization of the defence-eliciting salivary components indicates that Arabidopsis recognizes a proteinaceous elicitor with a size between 3 and 10 kD. Genetic analysis using well-characterized Arabidopsis mutants shows that saliva-induced resistance against M. persicae is independent of the known defence signalling pathways involving salicylic acid, jasmonate and ethylene. Among 78 Arabidopsis genes that were induced by aphid saliva infiltration, 52 had been identified previously as aphid-induced, but few are responsive to the well-known plant defence signalling molecules salicylic acid and jasmonate. Quantitative PCR analyses confirm expression of saliva-induced genes. In particular, expression of a set of O-methyltransferases, which may be involved in the synthesis of aphid-repellent glucosinolates, was significantly up-regulated by both M. persicae feeding and treatment with aphid saliva. However, this did not correlate with increased production of 4-methoxyindol-3-ylmethylglucosinolate, suggesting that aphid salivary components trigger an Arabidopsis defence response that is independent of this aphid-deterrent glucosinolate.
... In addition to acting as a salivary sheath, gelling saliva contains digestive enzymes that minimize mechanical injury to plant tissues [5,11]. After stylet penetration, a large amount of watery saliva is secreted into plant tissues, which contain bioactive components involved in the suppression or induction of plant defense responses [2,8,12,13]. With the help of a flow of saliva, phytophagous hemipterans suck out liquid nutrients from plants while simultaneously transmitting various plant diseases. ...
... Recently, numerous salivary proteins produced by phloem-feeding insects have been identified, and their secretion is crucial for safe and successful feeding [2,9,12,[14][15][16][17][18][19]. For instance, the salivary proteins Mp56, Mp57, and Mp58 secreted by the green peach aphid Myzus persicae inhibit insect fecundity by activating the plant defense response, whereas MpC002 and Mp2 are essential for successful feeding and reproduction by these aphids [12,[20][21][22]. ...
... Recently, numerous salivary proteins produced by phloem-feeding insects have been identified, and their secretion is crucial for safe and successful feeding [2,9,12,[14][15][16][17][18][19]. For instance, the salivary proteins Mp56, Mp57, and Mp58 secreted by the green peach aphid Myzus persicae inhibit insect fecundity by activating the plant defense response, whereas MpC002 and Mp2 are essential for successful feeding and reproduction by these aphids [12,[20][21][22]. In the brown planthopper Nilaparvata lugens, a notorious sap-sucking insect pest on rice in East Asia, the salivary proteins Nlshp and Nlsalivary protein-3 are indispensable for the formation of the salivary sheath and rice feeding [9,23]. ...
Saliva secretion is essential for successful feeding by piercing–sucking insects. Despite extensive studies of the saliva composition of phloem- and blood-feeding insects, less is known about the oral secretions of seed-feeding insects. The firebug Pyrrhocoris apterus is a polyphagous insect that feeds primarily on dry seeds of various plant species. Here, liquid chromatography‒mass spectrometry/mass spectrometry (LC‒MS/MS) was used to identify 165 P. apterus salivary proteins, including 110 gelling-specific proteins, 24 watery-specific proteins, and 31 proteins common to both groups. Transcriptomic analysis of saliva glands identified 567 potential salivary proteins, of which 87 overlapped with those detected by LC‒MS/MS. Comparative analysis showed that 98 out of 165 (59.4%) P. apterus saliva proteins were associated with extra-oral digestion and detoxification and had homologs in ten other species of arthropods examined. In addition, 67 proteins were specific to P. apterus, of which 22 proteins were defined with unknown functions. RNA interference-mediated gene silencing assays indicated that P. apterus-specific proteins were vital for P. apterus survival. Our findings shed light on the function of salivary proteins in feeding by seed-feeding insects and the evolution of feeding habits in piercing–sucking insects.
... For example, Myzus persicae (Sulzer) secrete cysteine protease cathepsin B3 (CathB3) into tobacco plants, which activates a reactive oxygen species defense response and inhibits the feeding of M. persicae [14]. The infiltration of M. persicae saliva or salivary components (in the range of 3-10 kDa) into Arabidopsis plants activates defense signaling and decreases M. persicae offspring number [15]. In addition, some salivary components are categorized as 'effectors', which can suppress plant defense. ...
... The tubes were placed in a climate chamber (25 • C, 16 h light: 8 h dark), and the sucrose diet collected 48 h later. Some saliva was boiled at 95 • C for 30 min to inactivate proteins [15]. Sucrose diets containing fresh, boiled, and control saliva samples were infiltrated into young C. sinensis leaves using a 1 mL syringe without the needle. ...
... This indicates that A. spiraecola saliva-induced phytohormone-dependent defense is faster and stronger than that induced by A. citricidus saliva. This modulation of plant defense responses by saliva has also been reported in other piercing-sucking insects, including B. tabaci [46], S. avenae [29], and M. persicae [15]. Moreover, the effect of citrus aphid saliva on plant defenses is similar to that induced by citrus aphid infestation, where both aphid species activated genes involved in SA-dependent defense, whereas A. spiraecola activated and A. citricidus repressed genes involved in JA-dependent defenses [25]. ...
The Asian citrus psyllid, Diaphorina citri Kuwayama, is one of the most important citrus pests because it transmits the bacterium that causes citrus Huanglongbing during feeding. The saliva of herbivorous insects can modulate plant defenses and, in turn, impact insect fitness, which is mostly studied in insects feeding on herbaceous plants. The role of saliva in the relationship between the Asian citrus psyllid and its woody host plant citrus, on the other hand, is unknown. Because two citrus aphid species, Aphis spiraecola Patch and Aphis (Toxoptera) citricidus (Kirkaldy), have a contrasting impact on the performance of subsequently infested D. citri, we explored the role of their saliva on D. citri feeding behavior and host plant defenses. We found that the infiltrating saliva of A. spiraecola into the host citrus leaves of the psyllid disrupted the subsequent feeding behavior of D. citri and also activated the expression of genes involved in plant salicylic acid (SA) and jasmonic acid (JA) defense pathways. By contrast, saliva infiltrations of A. citricidus (Kirkaldy) promoted D. citri feeding, activated the expression of one gene involved in the SA pathway, and repressed several genes involved in the JA pathway. We demonstrate that the saliva of aphids can affect D. citri performance, possibly by modulating plant defenses. This is the first study to show that insect saliva can influence D. citri feeding behavior by changing plant defenses.
... This response is also independent of the known defence signalling pathways involving salicylic acid, jasmonate and ethylene. The expression of a set of O-methyltransferases, which may be involved in the synthesis of aphid-repellent glucosinolates, was significantly up-regulated in infested leaves by both M. persicae feeding and treatment with aphid saliva [36]. ...
... There were 22 putative genes and 29 putative genes up-regulated after aphid feeding or mechanical wounding, respectively. However, the differences between treatments were greater, indicating the ability of the plant to distinguish between insect attack (in this case aphid feeding) and mechanical wounding, probably due to its recognition of insect salivary compounds [36] [47] [58] [59] [60]. ...
... This further supports the role of this gene in plant defense/tolerance, as there are a number of studies that describe the importance of tolerance to oxidative stress towards the survival of a plant under insect attack [18] [31] [62]. In addition to its role as an antioxidant, the ability of GST to detoxify endogenous and xenogenous compounds may also be important in plant defence/tolerance against aphid attack because phloem-feeding insects are known to inject their salivary compounds to sabotage plant defence [36] [47] [58] [59] [60]. ...
The responses of commercial wheat (cv. Claire) to grain aphid (Sitobion avenae) infestation and mechanical wounding were investigated in this study, with the aim to eventually identify a source of molecular markers to breed wheat for enhanced insect resistance, and in particular for enhanced resistance to phloem-feeding insects. Two cDNA subtractive hybridization libraries were constructed, one to identify transcripts involved in the responses to aphid infestation, and the second to identify transcripts involved in responses to mechanical wounding. Following subtractive hybridization, 520 and 800 clones were obtained from the subtractive hybridization between aphid-infested and un-infested wheat cDNAs and between mechanically wounded and un-wounded wheat cDNAs, respectively.Although the majority of differentially expressed putative genes after aphid infestation or mechanical wounding were involved in metabolic processes and photosynthesis, the majority of the genes expressed were different. Genes encoding glutathione transferase (GST), apoptosis and proteolysis were up-regulated after aphid feeding, suggesting their importance towards plant defence/tolerance against aphid attack.
... After Myzus persicae feeding and aphid saliva treatment, a set of O-methyltransferases involved in the synthesis of aphid-repellent GLS were significantly up-regulated based on qRT-PCR analyses of 78 genes. However, ITC production was not correlated with these gene expression level, suggesting that aphid salivary components trigger a defense response in Arabidopsis that is independent of the aphid-deterrent GLS [133]. In addition, aphid attack could increase indolyl GLS concentrations three-fold [134]. ...
... Pest invasion and disease infestation can increase GLS, especially indole GLS, in cruciferous plants [8,9,[89][90][91][92][93][94][95]105,117,[121][122][123]133,134]. In the case of rapeseed and other species that have low GLS, molecular biology techniques can be used to increase indole GLS production, which could improve resistance to diseases and insect, without increasing total GLS synthesis. ...
... No [131] Psylliodes chrysocephala positive [132] Ceutorhynchus obstrictus No [133] Indole GLS Fungal Albugo candida positive [94] Colletotrichum gloeosporioides Positive [95] Colletotrichum orbiculare Positive [95] Fusarium oxysporum positive [96,97] Plasmodiophora brassicae positive [102] Bacteria Pseudomonas syringae positive [106][107][108] Aliphatic GLS Fungal Plasmodiophora brassicae positive [102] Pest Spodoptera littoralis positive [125] Pieris brassicae positive [125] Pieris rapae positive [126] Insect Psylliodes chrysocephala positive [137] Aromatic GLS Fungal Plasmodiophora brassicae positive [102] Pest Plutella xylostella L. positive [60] Benzenic GLS Insect Psylliodes chrysocephala positive [136] Indolyl-3-acetonitrile, 4-methoxyglucobrassicin, Fungal Albugo candida positive [94] Aliphatic isopropyl; methylpropyl GLS Bacteria Erwinia carotovora positive [105] ...
With the expansion of the area under Cruciferae vegetable cultivation, and an increase in the incidence of natural threats such as pests and diseases globally, Cruciferae vegetable losses caused by pathogens, insects, and pests are on the rise. As one of the key metabolites produced by Cruciferae vegetables, glucosinolate (GLS) is not only an indicator of their quality but also controls infestation by numerous fungi, bacteria, aphids, and worms. Today, the safe and pollution-free production of vegetables is advocated globally, and environmentally friendly pest and disease control strategies, such as biological control, to minimize the adverse impacts of pathogen and insect pest stress on Cruciferae vegetables, have attracted the attention of researchers. This review explores the mechanisms via which GLS acts as a defensive substance, participates in responses to biotic stress, and enhances plant tolerance to the various stress factors. According to the current research status, future research directions are also proposed.
... For instance, silverleaf whitefly (SLWF) infestation of Arabidopsis, induces SA defenses and suppresses effectual JA defenses, and Arabidopsis mutants that activate SA defenses (cim10) or impair JA defenses (coi1) accelerate SLWF pupa development [35]. Similarly, Phenacoccus solenopsis infestation increases SA levels and decreases JA production, thereby repressing host antiherbivore defenses [36]. However, inconsistently, NahG-transgenic tomato, which eliminates endogenous SA production, was more susceptible to potato aphid compared with wild-type tomato. ...
... However, inconsistently, NahG-transgenic tomato, which eliminates endogenous SA production, was more susceptible to potato aphid compared with wild-type tomato. SA signaling mutants in Arabidopsis do not affect plant resistance to Myzus persicae but become more resistant to S. littoralis and B. tabaci [35,36]. These divergent results indicated that the impact of SA signaling on resistance to herbivorous insects is host or insect species dependent. ...
Upon infection with insect-borne microbial pathogens, plants are exposed to two
types of damage simultaneously. Over the past decade, numerous molecular
studies have been conducted to understand how plants respond to pathogens
or herbivores. However, investigations of host responses typically focus on a sin-
gle stress and are performed under static laboratory conditions. In this review,
we highlight research that sheds light on how plants deploy broad-spectrum
mechanisms against both vector-borne pathogens and insect vectors. Among
the host genes involved in multistress resistance, many are involved in innate
immunity and phytohormone signaling (especially jasmonate and salicylic
acid). The potential for genome editing or chemical modulators to fine-tune
crop defensive signaling, to develop sustainable methods to control insect-
borne diseases, is discussed.
... Recent technological advancements have spurred increased research into the salivary proteins of sucking insects, such as potato aphids [19], green peach aphids (Myzus persicae) [43], mirid bugs (Apolygus lucorum) [44], and whiteflies (Aleyrodidae) [45]. However, there is a notable gap in understanding the salivary components of Auchenorrhyncha species, particularly those that are phytophagous. ...
Saliva plays a crucial role in shaping the compatibility of piercing–sucking insects with their host plants. Understanding the complex composition of leafhopper saliva is important for developing effective and eco-friendly control strategies for the tea green leafhopper, Empoasca flavescens Fabrecius, a major piercing–sucking pest in Chinese tea plantations. This study explored the saliva proteins of tea green leafhopper adults using a custom collection device, consisting of two layers of Parafilm stretched over a sucrose diet. A total of 152 proteins were identified using liquid chromatography–tandem mass spectrometry (LC-MS/MS) following the filter-aided sample preparation (FASP). These proteins were categorized into six groups based on their functions, including enzymes, transport proteins, regulatory proteins, cell structure proteins, other proteins, and unknown proteins. Bioinformatics analyses predicted 16 secreted proteins, which were successfully cloned and transcriptionally analyzed across various tissues and developmental stages. Genes encoding putative salivary secretory proteins, including Efmucin1, EfOBP1, EfOBP2, EfOBP3, Efmucin2, low-density lipoprotein receptor-related protein (EfLRP), EFVg1, and EFVg2, exhibited high expressions in salivary gland (SG) tissues and feeding-associated expressions at different developmental stages. These findings shed light on the potential elicitors or effectors mediating the leafhopper feeding and defense responses in tea plants, providing insights into the coevolution of tea plants and leafhoppers. The study’s conclusions open avenues for the development of innovative leafhopper control technologies that reduce the reliance on pesticides in the tea industry.
... Vegetation minor metabolism as well supplies circuitous protection via enticing normal foes of pests [84,85,86,87]. Researches through mutants have detected that grass eater stimulated vegetation volatile substances (HIPV) emission demands the Jasmonate-marking passageway in Arabidopsis exposure to aphids [88,89] and in tomato exposure to hawkmoth larvae [90] however other devices could be various. The homoterpenes 4,8-dimethylnona-1,3,7-triene (DMNT) and 4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT) are amongst the generality common HIPVs output through angiosperms and the metabolic passageway and bio creation passageway supporting their manufacturing has been clarify in Arabidopsis [91]. ...
Co-evolved is the mostly passable opinion for the development of insect-harbor-cultivate connections, whilst, it enable be offered that its essential prelude are unsuitable: (1) generality Plant-eating insects have highly minimum inhabitance intensities comparison to the bio conglomerate of their harbor cultivates , subsequently, they ability seldom be significant chosen agents for the vegetative; (2) insect- harbor-cultivate reactions are not indispensable hostile: monoeater- and oligoeater insects, whether their count is obviously elevated, may perfect organize the multitude of their harbor cultivates (reciprocal usefulness); Therefore, (3) durability to insects is not a comprehensive needful in vegetation and it Not possible clarify the existence of subaltern vegetation materials; (4) equivalent development pathways of vegetations and insects which must outcome from co development reactions are scarce, whereas numerous intimately concerning insects nourish on Vegetarian highly Away vegetation Varieties - a connection which not possible be concerning to co- development. So, the opinion of successive development is suggested: the development of blossom vegetations encouraged via chosen agents (e.g., environment, ground, vegetation- vegetation, reactions etc.), which are numerous extra powerful than insect offensives originate the biochemically varied dietary rule for the development of Plant-eating insects, whereas the last do not Significantly impact the development of vegetations.
... The contamination of non-aphid proteins in aphid saliva may interfere with the result of salivary proteomic analysis. We collected aphid saliva using the same method as described previously [42,58,59] by collecting the artificial diet on which aphids had been fed for 24 h. During the feeding process, aphid stylet introduced some bacteria into the artificial diet (Wang et al., unpublished data). ...
Simple Summary
Aphids are generally dietary specialists, colonizing a specific plant or a group of closely related plants, but a few species are generalists, colonizing hundreds of hosts across multiple plant families. In these generalist aphids, host-specialized lineages or host-specialized biotypes are often observed in nature. This is the case for the cotton-melon aphid, Aphis gossypii Glover. When introduced to alternative hosts, the host-specialized biotypes show poor fitness and may even die within a few days. The underlying mechanisms of aphid host specialization remain unknown until now. We hypothesized that host-specialized biotypes express biotype-specific salivary effectors or elicitors that determine the compatibility of aphid-plant interactions. In this research, we described three strategies to identify biotype-specific effectors in two host-specialized biotypes of A. gossypii, a biotype specialized in Malvaceae and another in Cucurbitaceae. The strategy of combining transcriptome and proteome has the highest efficiency, obtaining less than one dozen effector candidates, and we strongly recommend this strategy to identify biotype-specific effectors in aphids and other sap-sucking insects.
Abstract
Polyphagous aphids often consist of host-specialized biotypes that perform poorly in non-native hosts. The underlying mechanisms remain unknown. Host-specialized biotypes may express biotype-specific salivary effectors or elicitors that determine aphid hosts. Here, we tried three strategies to identify possible effectors in Malvaceae- (MA) and Cucurbitaceae-specialized (CU) biotypes of the cotton-melon aphid Aphis gossypii Glover. The whole-aphid RNA-seq identified 765 differentially expressed genes (DEGs), and 139 of them were possible effectors; aphid-head RNA-seq identified 523 DEGs were identified, and 98 of them were possible effectors. The homologous genes of published aphid effectors were not differentially expressed between CU and MA. Next, quantitative proteomic analyses of saliva identified 177 possible proteins, and 44 of them were different proteins. However, none of the genes of the 44 proteins were differentially expressed, reflecting the discrepancy between transcriptome and proteome data. Finally, we searched for DEGs of the 177 salivary proteins in the aphid-head transcriptomes, and the salivary proteins with expression differences were regarded as effector candidates. Through this strategy, 11 effector candidates were identified, and their expression differences were all confirmed by RT-qPCR. The combinatorial analysis has great potential to identify biotype-specific effector candidates in aphids and other sap-sucking insects.
... To date, many studies have demonstrated that aphid saliva performs important roles in mediating the interactions between aphid and host plant (Elzinga and Jander, 2013;Yates and Michel, 2018). For example, the infiltration of salivary components in the 3-10 kDa fraction obtained from green peach aphid (Myzus persicae) induced the expression of defence-related genes in Arabidopsis thaliana and activated resistance against aphids, demonstrating the defenceeliciting activity of aphid salivary components (De Vos and Jander, 2009). Moreover, green peach aphid Myzus persicae salivary proteins Mp10, Mp42, Mp56, Mp57 and Mp58 1 decreased aphid reproduction when transiently expressed in tobacco plants Nicotiana benthamiana, highlighting their potential roles in activating plant defences (Bos et al., 2010;Rodriguez et al., 2014). ...
Aphid salivary proteins are critical in modulating plant defence responses. Grain aphid Sitobion miscanthi is an important wheat pest worldwide. However, the molecular basis for the regulation of the plant resistance to cereal aphids remains largely unknown. Here, we show that SmCSP4, a chemosensory protein from S. miscanthi saliva, is secreted into wheat plants during aphid feeding. Delivery of SmCSP4 into wheat leaves activates salicylic acid (SA)-mediated plant defence responses and subsequently reduces aphid performance by deterring aphid feeding behaviour. In contrast, silencing SmCSP4 gene via nanocarrier-mediated RNAi significantly decreases the ability of aphids to activate SA defence pathway. Protein-protein interaction assays showed that SmCSP4 directly interacts with wheat transcriptional factor TaWRKY76 in plant nucleus. Furthermore, TaWRKY76 directly binds to the promoter of SA degradation gene Downy Mildew Resistant 6 (DMR6) and regulates its gene expression as transcriptional activator. SmCSP4 secreted by aphids reduces the transcriptional activation activity of TaWRKY76 on DMR6 gene expression, which is proposed to result in increases of SA accumulation and enhanced plant immunity. This study demonstrated that SmCSP4 acts as salivary elicitor that is involved in activating SA signalling defence pathway of wheat by interacting with TaWRKY76, which provide novel insights into aphid-cereal crops interactions and the molecular mechanism on induced plant immunity.
... Honeydew is known to favor sooty mold species [22] and aphids were found to increase the abundance of culturable epiphytic fungi and bacteria on leaves and shoots of several forest tree species [23][24][25]. Moreover, aphids are known to deposit associated microbes in and on leaves and induce stress responses in plants [26][27][28][29][30]. Plant stress responses affect phyllosphere microbiomes as well [31]. ...
Background:
The effect of soil on the plant microbiome is well-studied. However, less is known about the impact of the soil microbiome in multitrophic systems. Here we examined the effect of soil on plant and aphid microbiomes, and the reciprocal effect of aphid herbivory on the plant and soil microbiomes. We designed microcosms, which separate below and aboveground compartments, to grow oak seedlings with and without aphid herbivory in soils with three different microbiomes. We used amplicon sequencing and qPCR to characterize the bacterial and fungal communities in soils, phyllospheres, and aphids.
Results:
Soil microbiomes significantly affected the microbial communities of phyllospheres and, to a lesser extent, aphid microbiomes, indicating plant-mediated assembly processes from soil to aphids. While aphid herbivory significantly decreased microbial diversity in phyllospheres independent of soil microbiomes, the effect of aphid herbivory on the community composition in soil varied among the three soils.
Conclusions:
This study provides experimental evidence for the reciprocal influence of soil, plant, and aphid microbiomes, with the potential for the development of new microbiome-based pest management strategies.
... In most insects, salivary glands are important labial glands that secrete saliva, an essential chemical substance with biological activities and complex composition, including many digestive enzymes (e.g., proteinases, phospholipase, esterase, serine proteases, trehalase) [14][15][16]. Like other mirid bugs, P. micranthus feed by inserting its stylet into plant tissues and injecting enzyme-containing saliva (digestive enzymes); the injected saliva is responsible for stylet lubrication and preliminary digestion of plant tissues [14,17,18]. ...
Background
The plant bug, Pachypeltis micranthus Mu et Liu (Hemiptera: Miridae), is an effective potential biological control agent for Mikania micrantha H.B.K. (Asteraceae; one of the most notorious invasive weeds worldwide). However, limited knowledge about this species hindered its practical application and research. Accordingly, sequencing the genome of this mirid bug holds great significance in controlling M. micrantha.
Results
Here, 712.72 Mb high-quality chromosome-level scaffolds of P. micranthus were generated, of which 707.51 Mb (99.27%) of assembled sequences were anchored onto 15 chromosome-level scaffolds with contig N50 of 16.84 Mb. The P. micranthus genome had the highest GC content (42.43%) and the second highest proportion of repetitive sequences (375.82 Mb, 52.73%) than the three other mirid bugs (i.e., Apolygus lucorum, Cyrtorhinus lividipennis, and Nesidiocoris tenuis). Phylogenetic analysis showed that P. micranthus clustered with other mirid bugs and diverged from the common ancestor approximately 200 million years ago. Gene family expansion and/or contraction were analyzed, and significantly expanded gene families associated with P. micranthus feeding and adaptation to M. micrantha were manually identified. Compared with the whole body, transcriptome analysis of the salivary gland revealed that most of the upregulated genes were significantly associated with metabolism pathways and peptidase activity, particularly among cysteine peptidase, serine peptidase, and polygalacturonase; this could be one of the reasons for precisely and highly efficient feeding by the oligophagous bug P. micranthus on M. micrantha.
Conclusion
Collectively, this work provides a crucial chromosome-level scaffolds resource to study the evolutionary adaptation between mirid bug and their host. It is also helpful in searching for novel environment-friendly biological strategies to control M. micrantha.
... [4][5][6][7][8] An increasing number of studies have characterized the protein components in the saliva of plant sap-feeding insects and explored their functions. [9][10][11][12][13] Some of these proteins have been demonstrated to be indispensable for feeding and survival of plant sap-sucking hemipterans. [14][15][16][17][18][19] The oral secretion of piercing-sucking herbivores mainly contains gelling and watery saliva, 20,21 which can, respectively, facilitate the penetration of stylet sheath and mitigation of antiherbivore defense. ...
BACKGROUND
Phenacoccus solenopsis is a polyphagous invasive mealybug that caused serious damage to crops worldwide. Phloem‐sucking hemipterans are known to carry symbiotic microbes in their saliva. However, the role of salivary bacteria of P. solenopsis in modulating plant defenses remains limited. Exploring the impact of salivary bacteria on plant defense responses will contribute to the development of new targets for efficient control of invasive mealybugs.
RESULTS
Salivary bacteria of the invasive mealybug P. solenopsis can suppress herbivore‐induced plant defenses and thus enhance mealybug fitness. Mealybugs treated with an antibiotic showed decreased weight gain, fecundity and survival. Untreated mealybugs suppressed jasmonic acid (JA)‐regulated defenses but activated salicylic acid (SA)‐regulated defenses in cotton plants. In contrast, antibiotic‐treated mealybugs triggered JA‐responsive gene expression and JA accumulation, and showed shortened phloem ingestion. Reinoculating antibiotic‐treated mealybugs with Enterobacteriaceae or Stenotrophomonas cultivated from mealybug saliva promoted phloem ingestion and fecundity, and restored the ability of mealybugs to suppress plant defenses. Fluorescence in situ hybridization visualization revealed that Enterobacteriaceae and Stenotrophomonas colonize salivary glands and are secreted into the mesophyll cells and phloem vessels. Exogenous application of the bacterial isolates to plant leaves inhibited JA‐responsive gene expression and activated SA‐responsive gene expression.
CONCLUSION
Our findings imply that symbiotic bacteria in the saliva of the mealybug play an important role in manipulating herbivore‐induced plant defenses, enabling this important pest to evade induced plant defenses and promoting its performance and destructive effects on crops. © 2023 Society of Chemical Industry.
... The saliva protein is recognized by the plants, triggering the activation of defensive mechanisms, as 'elicitors'. They can also act as 'effectors', suppressing plant defense signaling, thereby increasing the performance of the herbivores (Mutti et al., 2008;de Vos & Jander, 2009;Bos et al., 2010;Atamian et al., 2013;Pitino & Hogenhout, 2013;Chaudhary et al., 2014;Elzinga et al., 2014;Guo et al., 2014;Wang et al., 2015;Naessens et al., 2015;Thorpe et al., 2016;Kettles & Kaloshian, 2016;Rodriguez et al., 2017;reviewed in Yates & Michel, 2018). ...
Prior to feeding on phloem, aphids perform a preamble of brief intracellular punctures of the cortical parenchyma, ingesting a small amount of cytoplasm from each cell. Given the length of time aphids spend puncturing parenchyma cells before and after phloem feeding, we propose that they are not just testing for potential hosts or mobilizing phloem nutrients, but are actively engaged in ‘cytoplasmic feeding’. We combine the electrical penetration graph (EPG) technique to monitor feeding behavior of Myzus persicae (Sulzer) (Hemiptera: Aphididae) with confocal fluorescence microscopy to determine the uptake of parenchyma cytoplasm in the model plant Arabidopsis thaliana (L.) Heynh. (Brassicaceae). Aphids repetitively punctured parenchyma cells throughout the monitoring period, both before and after phloem feeding. As aphids puncture parenchyma cells of A. thaliana expressing cytoplasmic yellow fluorescent protein, the protein is ingested, increasing the intensity in the aphid stylet. The extended time of high‐frequency punctures of parenchyma cells prior to phloem sap ingestion avoids the dilution of the intestinal content resulting from immediate phloem feeding. The enriched nutrient content of parenchyma cytoplasm has time to be absorbed by the intestine into the hemocoel without dilution and excretion in the honeydew.
... During feeding, these insects inject secreted saliva into plant tissues to fix and digest nutrients, acting as effectors to facilitate feeding on the host plant Huang et al., 2021). In recent years, with continuous technological advances, some salivary proteins acting as effectors were identified from white-backed planthopper (Sogatella furcifera), brown planthopper (Nilaparvata lugens), green peach aphid (Myzus persicae), potato aphid (Macrosiphum euphorbiae), mirid bug (Apolygus lucorum), and white flies (Aleyrodidae) (Chaudhary et al., 2014;De Vos & Jander, 2009;Dong et al., 2020;Miao et al., 2018;Rao et al., 2019;Shangguan et al., 2018;Xu, Qian, et al., 2019). Additionally, it is widely recognized that salivary proteins released by insects into plants are transported inside the host, employing a versatile strategy to suppress plant defence responses to establish successful feeding . ...
The bean bug (Riptortus pedestris), one of the most important pests of soybean, causes staygreen syndrome, delaying plant maturation and affecting pod development, resulting in severe crop yield loss. However, little is known about the underlying mechanism of this pest. In this study, we found that a salivary secretory protein, Rp614, induced cell death in nonhost Nicotiana benthamiana leaves. NbSGT1 and NbNDR1 are involved in Rp614-induced cell death. Tissue specificity analysis showed that Rp614 is mainly present in salivary glands and is highly induced during pest feeding. RNA interference experiments showed that staygreen syndrome caused by R. pedestris was significantly attenuated when Rp614 was silenced. Together, our results indicate that Rp614 plays an essential role in R. pedestris infestation and provide a promising RNA interference target for pest control.
... Feeding by M. persicae from the phloem of Arabidopsis thaliana did not bring myrosinase from adjacent cells into contact with glucosinolates, whereas feeding by chewing herbivores did (De Vos and Jander, 2010). In addition, aphids secrete hydrolytic enzymes, such as lipases and peroxidases, in the phloem sap during feeding (De Vos and Jander, 2009). Lipases and peroxidases alter the expression of genes such as PR-proteins associated with the SA-signalling pathway (Zhu-Salzman et al., 2004;Moran and Thompson, 2001). ...
Damage to a host plant caused by insect herbivory and pathogens induces defence responses in the plant. Defence responses induced by hemipterans are often distinct from those elicited by chewing herbivores. Furthermore, hemipterans and pathogens induce a similar set of specific responses, which cannot only affect different species of insect herbivores, but also reduce the severity and symptoms of pathogen attack. Moreover, hemipteran predators can also induce plant resistance against insect herbivory, e.g. by probing/feeding attempts or via ovipositing into plant tissue. The aim of this review was to review only studies that involved direct induced resistance, induced by insects, such as hemipterans and predators, on subsequent attack by insect pests and pathogens. The criterion applied was that a reduced activity of the aggressors was measured, accompanied by direct defence responses. Studies on herbivore-induced plant volatiles (HIPVs) were excluded as our focus is on induced resistance that would also have effect on pathogens that cannot themselves respond to HIPVs. Out of a total of 375 studies generated by a systematic search, 24 studies fulfilled the criteria. The review shows that the release of hemipteran predators for biological control in greenhouses may also lead to induced resistance against subsequent attackers. Monitoring of hemipterans and plant diseases are used to inform early warning systems for pest management. Accordingly, a thorough understanding of the responses induced by hemipterans can facilitate further progress in crop protection strategies in both greenhouse facilities and in open field productions.
... During aphid infestation, the content of betulin in the phloem sap of R-32 first decreased and then increased slightly ( Figure S2); this decreasing trend in the betulin content may be induced by aphid infestation. Aphid-infestation can modulate gene expression 43 and secondary metabolites levels in plants. 44 Plant−aphid interaction is a complicated molecular warfare battle. ...
Wild pest-resistant germplasms employ secondary metabolites to withstand insect attacks. A close wild relative of the cultivated peach, Prunus davidiana, displays strong resistance to green peach aphids by utilizing metabolites to cope with aphid infestation; however, the underlying mechanism of aphid resistance remains mostly unknown. Here, metabolomic analysis was performed to explore the changes in metabolite levels in P. davidiana after aphid infestation. The data revealed that betulin is a key defensive metabolite in peaches that protects against aphids and possesses potent aphidicidal activity. Further toxicity tests demonstrated that betulin was toxic to pests but not to beneficial insects. Additionally, transcriptomic and phylogenetic analyses revealed that the cytochrome P450 gene PpCYP716A1 was responsible for betulin synthesis─this finding was confirmed by the heterologous expression of this gene. This study revealed a strategy whereby plants harness defense metabolites to develop resistance to pests. These findings may facilitate controlling such pests.
... The eliciting activity of aphid salivary proteins in plant defence responses was also detected. The infiltration of the watery saliva of M. persicae and the grain aphid Sitobion avenae induced plant defence responses and had adverse effects on aphid performance and feeding behaviour (De Vos and Jander, 2009;Zhang et al., 2017). Transient overexpression of Mp10 and Mp42 activated plant defence in N. benthamiana and reduced aphid fecundity (Rodriguez et al., 2014). ...
Aphids secrete diverse repertoires of salivary effectors into host plant cells to promote infestation by modulating plant defense. The greenbug Schizaphis graminum is an important cereal aphid worldwide. However, the secreted effectors of S. graminum are still uncharacterized. Here, 76 salivary proteins were identified from the watery saliva of S. graminum using transcriptome and proteome analyses. Among them, a putative salivary effector Sg2204 was significantly upregulated during aphid feeding stages, and transient overexpression of Sg2204 in Nicotiana benthamiana inhibited cell death induced by BAX or INF1. Delivering Sg2204 into wheat via the type III secretion system of Pseudomonas fluorescens EtAnH suppressed pattern‐triggered immunity (PTI)‐associated callose deposition. The transcript levels of jasmonic acid (JA)‐ and salicylic acid (SA)‐associated defense genes of wheat were significantly downregulated, and the contents of both JA and SA were also significantly decreased after delivery of Sg2204 into wheat leaves. Additionally, feeding on wheat expressing Sg2204 significantly increased the weight and fecundity of S. graminum and promoted aphid phloem feeding. Sg2204 was efficiently silenced via spray‐based application of the nanocarrier‐mediated transdermal dsRNA delivery system. Moreover, Sg2204‐silenced aphids induced a stronger wheat defense response and resulted in negative impacts on aphid feeding behavior, survival, and fecundity. Silencing of Sg2204 homologs from four aphid species using nanocarrier‐delivered dsRNA also significantly reduced aphid performance on host plants. Thus, our study characterized the salivary effector Sg2204 of S. graminum involved in promoting host susceptibility by suppressing wheat defense, which can also be regarded as a promising RNAi target for aphid control.
... For example, Ram et al. (2017) used microarray data to identify a set of reliable candidate RGs for qRT-PCR validation under Brassica juncea-aphid interaction. The microarray data of Arabidopsis-aphid interaction (De Vos and Jander, 2009) was downloaded by considering single experimental Genevestigator tool (Hruz et al., 2008). In order to define ratio of false positives amongst significant results, a binary matrix test with threshold of 0.5 false discovery rate (FDR) was performed. ...
Quantitative reverse transcription polymerase chain reaction (qRT-PCR) is extensively applied technique to investigate the transcript abundance of target genes in various organisms. Selection of appropriate reference genes (RGs) for qRT-PCR normalization is a crucial prerequisite for accurately quantifying gene expression level. RGs should exhibit minimal variation in gene expression. However, the actual expression stability of RGs fluctuates greatly in different species or under different experimental conditions. Due to rapid advancements in next-generation sequencing (NGS) technology, it is no longer difficult to get massive transcriptome data, which has greatly promoted the development of RGs. In this review, we elaborate on the strategies for developing RGs using Northern blotting, expressed sequence tags (ESTs), qRT-PCR, and high-throughput technologies such as microarray and RNA sequencing
(RNA-Seq). The process for developing RGs based on RNA-Seq is further addressed, including processing and normalization of RNA-Seq data, evaluation of gene expression stability, and screening and validation of RGs. The most frequently used RGs in horticultural plants are summarized, and the strategies for developing these RGs are introduced in detail. The information provided here will help to design effective strategies for the development of RGs in horticultural plants, with a focus on using big data generated by RNA-Seq.
... These defense responses usually involve the expression of some proteins which strongly interact with the pathogen and its associated molecular patterns (PAMPS) (Kehr, 2006;Ernst et al., 2012), resulting in transmission of alarm signals (systemic acquired resistance, SAR) from the attacked parts to the entire plant (Van Bel, 2003). Plants defend themselves against stress by using the phloem-based defense (PBD) mechanism, which can be induced by wounding and oxidative stress as well as insect attack (Will and Van Bel, 2006;De Vos and Jander, 2009;Jiang et al., 2019). The translocation of proteins and RNAs between sieve elements and companion cells may play a pivotal role in SAR and other forms of remote signaling (Van Bel, 2003). ...
Much of the plant lectin research has focused on these proteins from seeds, whereas lectins from other plant tissues have been less investigated. Although presence of lectins in the phloem exudate of Cucurbitaceae species was reported over 40 years ago, only a few proteins from this family have been purified and characterized with respect to ligand binding properties, primary and secondary structures, while no 3D structure of a member of this family is known so far. Unlike lectins from other plant families and sources (e.g., seeds and tubers), which exhibit specificity towards different carbohydrate structures, all the Cucurbitaceae phloem exudate lectins characterized so far have been shown to recognize only chitooligosaccharides or glycans containing chitooligosaccharides. Interestingly, some of these proteins also bind various types of RNAs, suggesting that they may also play a role in the transport of RNA information molecules in the phloem. The present review gives an overview of the current knowledge of Cucurbitaceae phloem exudate lectins with regard to their purification, determination of primary and secondary structures, elucidation of thermodynamics and kinetics of carbohydrate binding and computational modeling to get information on their 3D structures. Finally, future perspectives of research on this important class of proteins are considered.
... In some plant genotypes, one or more salivary proteins can be recognized by the host to elicit defenses. Indeed, saliva collected from the GPA feeding on an artificial diet was capable of eliciting plant defenses and the active component was determined to be proteinaceous (De Vos and Jander, 2009). Cathepsin Bs, which are papain-like cysteine proteases that are highly expressed in the GPA in response to host change, represent one such salivary protein family. ...
The location of the phloem deep inside the plant, the high hydrostatic pressure in the phloem, and the composition of phloem sap, which is rich in sugar with a high C:N ratio, allows phloem sap feeding insects to occupy a unique ecological niche. The anatomy and physiology of aphids, a large group of phytophagous insects that use their mouthparts, which are modified into stylets, to consume large amounts of phloem sap, has allowed aphids to successfully exploit this niche, however, to the detriment of agriculture and horticulture. The ability to reproduce asexually, a short generation time, the development of resistance to commonly used insecticides, and their ability to vector viral diseases makes aphids among the most damaging pests of plants. Here we review how plants utilize their ability to occlude sieve elements and accumulate antibiotic and antinutritive factors in the phloem sap to limit aphid infestation. In addition, we summarize progress on understanding how plants perceive aphids to activate defenses in the phloem.
... 3.1.1. La défense contre les herbivores exogènes, telle les sécrétions orales des herbivores, appelés Herbivore-associated molecular pattern (HAMP) ou par des molécules endogènes de la plante, les Damage-associated molecular pattern (DAMP), produits à partir des fragments des cellules endommagées (Jones et Dangl, 2006;De Vos et Jander, 2009;Zhang et al., 2018). Les HAMP et les DAMP Herbivore-triggered immunity (HTI) (Erb et al., 2012) qui fonctionne entre autres par la synthèse et la signalisation JAs qui est spécifiquement nommée la JA-triggered immunity (JATI) (Campos et al., 2014) e et très rapide, elle commence à être quantifiable dans les deux minutes qui suivent le stress (Glauser et al., 2008). ...
Pour se défendre contre les herbivores ou les microorganismes nécrotrophes les plantes supérieures utilisent les jasmonates (JAs), en particulier l’hormone jasmonoyl-isoleucine (JA-Ile), pour activer la signalisation défensive. Les JAs régulent aussi des réponses contre des stress abiotiques. Mes travaux de thèse ont prouvé l’importance d’une signalisation JAs basale, et sa répression par trois oxydases d’acide jasmonique nommées JAO, dont l’action définit un mécanisme de détournement métabolique inédit. En aval de l'action du JA-Ile, deux voies cataboliques distinctes sont activées pour atténuer la signalisation induite. A l’aide de nouvelles lignées de plantes bloquées, pour l’une, l’autre ou les deux voies, mes recherches ont démontré leurs rôles respectifs dans l’élimination du JA-Ile en réponse à l’herbivorie ou à l’infection. Elles ont révélé qu’un catabolisme ralenti du JA-Ile limite sélectivement le gain en défense lorsque des régulateurs négatifs de la signalisation sont surstimulés. Nos résultats apportent de nouvelles connaissances sur les mécanismes cataboliques des JAs régulant les signalisations basales et induites.
... De Vos and Jander showed that injection of M. persicae saliva into A. thaliana leaves caused local aphid resistance. Subsequent fractionation of M. persicae saliva lead to a 3-10 kDa proteinaceous fraction responsible for this resistance (De Vos and Jander, 2009 Yang et al., 2017;Lee et al., 2018;Su et al., 2019;Wang et al., 2019;Xu et al., 2019). These effectors and their in planta locations and modes of action are illustrated in Figures 1A,B, respectively. ...
The Bemisia tabaci species complex (whitefly) causes enormous agricultural losses. These phloem-feeding insects induce feeding damage and transmit a wide range of dangerous plant viruses. Whiteflies colonize a broad range of plant species that appear to be poorly defended against these insects. Substantial research has begun to unravel how phloem feeders modulate plant processes, such as defense pathways, and the central roles of effector proteins, which are deposited into the plant along with the saliva during feeding. Here, we review the current literature on whitefly effectors in light of what is known about the effectors of phloem-feeding insects in general. Further analysis of these effectors may improve our understanding of how these insects establish compatible interactions with plants, whereas the subsequent identification of plant defense processes could lead to improved crop resistance to insects. We focus on the core concepts that define the effectors of phloem-feeding insects, such as the criteria used to identify candidate effectors in sequence-mining pipelines and screens used to analyze the potential roles of these effectors and their targets in planta. We discuss aspects of whitefly effector research that require further exploration, including where effectors localize when injected into plant tissues, whether the effectors target plant processes beyond defense pathways, and the properties of effectors in other insect excretions such as honeydew. Finally, we provide an overview of open issues and how they might be addressed.
... An induced defense response by aphids has been examined in numerous aphid-plant systems. For example, Myzus persicae showed declining fecundity over time in aphid infested leaves of Arabidopsis thaliana (De Vos and Jander 2009). Feeding of aphids caused increased volatile organic compound emission in chilli plants, with another repulsive effect on whitefly (Saad et al. 2015). ...
The destructive aphid (Sitobion avenae) of wheat, generally accomplished by chemical pesticides, is responsible for the substantial agricultural damages that occur annually. The present experimental study, a protein elicitor, PeBL1, has been examined for the possibility of inducing a defense response to S. avenae in wheat. In comparison to the positive (Water) and negative 70.58 μg ml −1 (50 mM Tris-HCl, pH 8.0) controls, the population growth (intrinsic Increase) rates of S. avenae (second and third generation) with PeBL1-treated wheat seedlings declined. S. avenae preferred control plants for colonizing in an experiment with the host selection compared with the PeBL1-treated wheat plants, with PeBL1 treated wheat seedlings; the nymphal development time of aphid has been extended. In comparison with positive (water) and negative controls, less fecundity was observed with less offspring's in PeBL1-treated wheat seedlings. S. avenae had a harmful surface environment for wheat seedlings treated with PeBL1, caused by trichomes and wax formation. The level of Jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) was significantly higher, and the PeBL1 treated wheat seedlings had significant accumulations. The findings presented that PeBL1 considerably altered the wheat surface structure so that the replication of S. avenae was minimized and colonization was prevented. Defensive processes also include pathway activation (JA, SA, and ET). A bio-control study for the use of PeBL1 in the protection against S. avenae has been produced in this area.
... The effects of glucosinolates have also been investigated on some other phloem-feeding insects such as the green peach aphid Myzus persicae, mostly using Arabidopsis mutants as the test plants; the results indicate that glucosinolates in general have limited influence on the performance of the test insects. 17,20,[33][34][35] Under natural conditions, activation of the classic myrosinaseglucosinolates chemical defense system relies on the direct contact of myrosinase and glucosinolates that were stored in different cells and released upon tissue damage. 36 Unlike their counterparts with chewing mouthparts, phloem-feeding insects such as whitefly feeds on plants with their stylets that only cause minor tissue damage. ...
BACKGROUND
While plant glucosinolates are known to impart resistance to many insects, their role in the interactions between plants and many phloem‐feeding insects such as whiteflies are poorly understood. The whitefly Bemisia tabaci complex comprises many cryptic species that differ in the ability to utilize Brassica plants. However, whether Brassica plants‐specific traits such as glucosinolates determine differences of whiteflies in colonizing Brassica plants remains in question.
RESULTS
We first observed performance of two whitefly species MEAM1 and Asia II 3, which differ obviously in their ability to colonize Brassica plants, on four cultivars of three Brassica species that vary in glucosinolate profile. We found that the life history characteristics of each of the two whitefly species seems to be only marginally affected by cultivar. We next used wild‐type Arabidopsis plants and mutants defective in glucosinolate biosynthesis or hydrolysis to explore the effects of glucosinolates on the whitefly. We found that fecundity and development of immature stages of neither of the two whitefly species differ significantly between wild‐type and mutants.
CONCLUSION
The data suggest that glucosinolates may have little effect on the oviposition by adults and the survival and development of immature stages of MEAM1 and Asia II 3 whiteflies. The marked differences in colonizing Brassica crops between the two whitefly species are likely due to plant traits other than glucosinolates. © 2021 Society of Chemical Industry.
... Indeed, for adult Sitobion avenae Fabricius, a higher survival of alate compared to apterous adults under starvation was found (Xu et al., 2012). Morphological and chemical plant defenses against aphids have to be considered as well (de Vos & Jander, 2009;Nalam et al., 2018;Dancewicz et al., 2020). In general, for herbivores, there is a trade-off between nutrient intake and ingestion of harmful compounds (Behmer, 2009). ...
Aphids feed on the phloem sap of their host plants. The chemical composition of this sap differs between plant species and is modulated by environmental factors. To understand why Myzus persicae (Sulzer) (Hemiptera: Aphididae) is able to infest various plant taxa, we investigated how aphids of this species respond to various sucrose‐to‐amino acid ratios of their diet. Moreover, we studied whether they are able to recover from periods with suboptimal nutrition. Preference and performance bioassays were performed using artificial diets with sucrose‐to amino acid ratios of 2.4:1 (optimal ‘control’ diet), 4.8:1 (‘high sucrose’), 1.2:1 (‘high amino acids’), or 1:0 (‘no amino acids’). Also, the capacity to recover from periods on suboptimal diet (i.e., the ‘no amino acids’ diet) was assessed. In four‐choice assays, both nymphs and adults of M. persicae were rarely found on the ‘no amino acids’ diet and they were similarly distributed on the other diets. As long as amino acids were available, the sucrose‐to‐amino acid ratio had only minor effects on aphid development and reproduction. On the suboptimal diet, nymphs survived, but with almost no weight gain over time. After transfer to the ‘control’ diet, they gained weight and reproduced with only low fitness deficits compared to aphids kept on the ‘control’ diet for the whole time. The capacity to survive under suboptimal nutrition and recover from it was dependent on the length of the period on the suboptimal diet. The ability to cope with different dietary sucrose‐to‐amino acid ratios and to withstand suboptimal nutrition for several days may contribute to the broad host plant spectrum of M. persicae and may explain why this species is a serious pest in agricultural systems.
... Aphids feed on phloem sap using piercing-sucking mouthparts and secrete saliva that can contain hundreds of different polypeptides derived from aphids and their symbionts (van Bel & Will, 2016;Chaudhary et al., 2014Chaudhary et al., , 2015Elzinga & Jander, 2013;Harmel et al., 2008). Several studies suggest that certain components of aphid saliva may trigger an oxidative burst and other signalling events similar to plant responses to effector molecules from plant pathogens (Bos et al., 2010;Chaudhary et al., 2014;de Vos & Jander, 2009;Rodriguez et al., 2014). Moreover, aphid saliva contains oxidizing enzymes such as polyphenoloxidases and peroxidases that may directly generate ROS (Miles, 1999). ...
The green peach aphid (Myzus persicae) is a phloem‐feeding insect that causes economic damage on a wide array of crops. Using a luminol‐based assay, a superoxide‐responsive reporter gene (Zat12::luciferase), and a probe specific to hydrogen peroxide (HyPer), we demonstrated that this aphid induces accumulation of reactive oxygen species (ROS) in Arabidopsis thaliana. Similar to the apoplastic oxidative burst induced by pathogens, this response to aphids was rapid and transient, with two peaks occurring within 1 and 4 hr after infestation. Aphid infestation also induced an oxidative response in the cytosol and peroxisomes, as measured using a redox‐sensitive variant of green fluorescent protein (roGFP2). This intracellular response began within minutes of infestation but persisted 20 hr or more after inoculation, and the response of the peroxisomes appeared stronger than the response in the cytosol. Our results suggest that the oxidative response to aphids involves both apoplastic and intracellular sources of ROS, including ROS generation in the peroxisomes, and these different sources of ROS may potentially differ in their impacts on host suitability for aphids. Green peach aphid infestation on Arabidopsis induces intracellular as well as extracellular generation of reactive oxygen species and triggers oxidative conditions in the cytosol and peroxisomes.
... Additionally, mutants of different DNA methylation, RdDM and small RNA pathways regulate immunity to bacterial and fungal infection (Agorio & Vera, 2007;Lopez et al., 2011;Dowen et al., 2012;Yu et al., 2013). Intriguingly, some biotic stresses can induce tolerance towards the pathogen in the subsequent generation (Boyko et al., 2007;De Vos & Jander, 2009;Boyko et al., 2010;Kathiria et al., 2010;Slaughter et al., 2012), a phenomenon that could be explained by changes in the methylation status of the DNA or chromatin rather than by spontaneous mutagenesis and reversion (Boyko & Kovalchuk, 2011;Annacondia & Martinez, 2019). ...
Environmentally induced changes in the epigenome help individuals to quickly adapt to fluctuations in the conditions of their habitats.
We explored those changes in Arabidopsis thaliana plants subjected to multiple biotic and abiotic stresses, and identified transposable element (TE) activation in plants infested with the green peach aphid, Myzus persicae. We performed a genome‐wide analysis mRNA expression, small RNA accumulation and DNA methylation
Our results demonstrate that aphid feeding induces loss of methylation of hundreds of loci, mainly TEs. This loss of methylation has the potential to regulate gene expression and we found evidence that it is involved in the control of plant immunity genes. Accordingly, mutant plants deficient in DNA and H3K9 methylation (kyp) showed increased resistance to M. persicae infestation.
Collectively, our results show that changes in DNA methylation play a significant role in the regulation of the plant transcriptional response and induction of defense response against aphid feeding.
... Similarly, when pectinases in the saliva of S. avenae are applied to wheat, they trigger indirect plant defense response by activating the discharge of volatiles that draw the parasitoid wasp Aphidius avenae (Liu et al. 2009). M. persicae salivary protein, a heat-sensitive peptide between 3 and 10 kDa, can induce defense against the aphid in A. thaliana plants and reduce aphid performance (De Vos and Jander 2009). Several other salivary HAMPs of M. persicae have been shown to be harmful to aphids and decrease their fecundity on A. thaliana and N. tabacum by initiating defense reactions (Bos et al. 2010;Elzinga et al. 2014). ...
Being sessile organisms, plants have evolved a vast range of resistance mechanism to offset biotic stress caused by insect herbivores. The coevolution of plants and insect herbivores has not only generated advanced defense strategies in plants but also led to development of feeding strategies and counter-adaptive mechanisms in insects. Several plant species can differentiate insect attack from mechanical damage by the perception of a suite of chemical signals or herbivore-associated elicitors (HAEs), also known as herbivore-associated molecular patterns (HAMPs), produced by the insect. HAMPs could arise from insect oral secretions (OS), saliva, digestive waste products, and ovipositional fluids. Apart from elicitors, OS from some insect herbivores also contain effectors that suppress plant antiherbivore defenses. HAEs are dissimilar in their origin and structure, ranging from FACs (fatty acid-amino acid conjugates) such as volicitin, chemically related oxylipins, sulfur-containing fatty acids (caeliferins), peptides (systemins and inceptins) to high-molecular-weight enzymes (glucose oxidase and glucosidase). The perception of HAEs leads to the commencement of specific physiological processes in plants in order to defend themselves from insect attack. These responses can vary from changes in plant’s metabolic activity and gene expression pattern to changes in their overall growth and development. Some HAEs are also known to counteract the defense response of plants. However, relatively less is known about the molecular components used by plants to perceive and recognize HAEs and the downstream signaling pathways leading to the initiation of plant response. In this chapter, we will focus on the recent developments made in the field of insect HAEs and their role in modulating plant defenses which will provide novel insights into our understanding of the interaction between plant and insects.
... In some instances, HAMPs in the saliva of piercing-sucking insects can elicit plant defence responses. A protein component of the saliva of the aphid Myzus persicae (green peach aphid) elicited defensive responses in Arabidopsis, although the identity of the protein component (between 3-10 kD) is unknown (De Vos & Jander, 2009). Enzymes in the saliva of the grain aphid, Sitobion avenae, may be responsible for inducing indirect defences in wheat; salivary pectinase elicited the production of volatile sulcatol and sulcatone, which were identified only in the pectinase-treated plants and aphiddamaged plants ). ...
In order to mount a successful defence, plants must specifically recognize the threat (microbe vs. herbivore), elicit the appropriate signalling pathway (e.g. salicylic acid vs. jasmonic acid) and mount the proper defence. As effective counterploys, herbivores may disrupt defence signalling to suppress defences, detoxify defences, or even sequester these defences in their bodies to avoid toxicity. Our current research has focused on salivary effectors that disrupt plant defence signalling. Our hypothesis is that, as an alternative counterploy, some herbivores may present themselves in ‘disguise’ and thus avoid proper detection. We believe this alternative counterploy has been overlooked, but that it may represent a commonly used strategy by certain herbivores. Emerging evidence suggest that some herbivores may actively deposit microbes in their oral secretions on plants, and thus be ‘mistakenly’ recognized as microbes. Consequently, plants turn on the incorrect signalling pathway and express defences that are ineffective against these intruders.
... Two key enzymes are involved in the SA biosynthesis in plants -phenylalanine ammonia lyase (PAL) and isochorismate synthase (ICS) -using phenylalanine and chorismate as the substrates, respectively (Wildermuth et al., 2001;Vlot et al., 2009; Figure 1.8). Phloem-feeding insects, such as aphids and silverleaf whiteflies, induce transcriptional responses in plants somewhat similar to those induced by SA treatment or attack from biotrophic pathogens (De Vos and Jander, 2009;Thaler et al., 2010). ...
The recognition of phytophagous insects by plants induces a set of very specific responses aimed at deterring tissue consumption and reprogramming plant metabolism and development to tolerate herbivory. This recognition requires the plant's ability to perceive chemical cues generated by the insects and to distinguish a particular pattern of tissue disruption.
Relatively little is known about the molecular basis of insect perception by plants and the signalling mechanisms directly associated with this perception. Importantly, the insect feeding behaviour (piercing‐sucking versus chewing) is a decisive determinant of the plant's defence response, and the mechanisms used to perceive insects from different feeding guilds may be distinct. During insect feeding, components of the saliva of chewing or piercing‐sucking insects come into contact with plant cells, and elicitors or effectors present in this insect‐derived fluid are perceived by plant cells to initiate the activation of specific signalling cascades.
Aphid salivary proteins mediate the interaction between aphids and their host plants. Moreover, these proteins
facilitate digestion, detoxification of secondary metabolites, as well as activation and suppression of plant defenses.
The cowpea aphid, Aphis craccivora, is an important sucking pest of leguminous crops worldwide.
Although aphid saliva plays an important role in aphid plant interactions, knowledge of the cowpea aphid
salivary proteins is limited. In this study, we performed transcriptomic and LC-MS/MS analyses to identify the
proteins present in the salivary glands and saliva of A. craccivora. A total of 1,08,275 assembled transcripts were
identified in the salivary glands of aphids. Of all these assembled transcripts, 53,714 (49.11%) and 53,577
(49.48%) transcripts showed high similarity to known proteins in the Nr and UniProt databases, respectively. A
total of 2159 proteins were predicted as secretory proteins from the salivary gland transcriptome dataset, which
contain digestive enzymes, detoxification enzymes, previously known effectors and elicitors, and potential
proteins whose functions have yet to be determined. The proteomic analysis of aphid saliva resulted in the
identification of 171 proteins. Tissue-specific expression of selected genes using RT-PCR showed that three genes
were expressed only in the salivary glands. Overall, our results provide a comprehensive repertoire of cowpea
aphid salivary proteins from the salivary gland and saliva, which will be a good resource for future effector
functional studies and might also be useful for sustainable aphid management.
Although phloem-feeding insects such as aphids can cause significant damage to plants, relatively little is known about early plant defenses against these insects. As a first line of defense, legumes can stop the phloem mass flow through a conformational change in phloem proteins known as forisomes in response to Ca2+ influx. However, specialized phloem-feeding insects might be able to suppress the conformational change of forisomes and thereby prevent sieve element occlusion. To investigate this possibility, we triggered forisome dispersion through application of a local heat stimulus to the leaf tips of pea (Pisum sativum), clover (Trifolium pratense) and broad bean (Vicia faba) plants infested with different pea aphid (Acyrthosiphon pisum) host races and monitored forisome responses. Pea aphids were able to suppress forisome dispersion, but this depended on the infesting aphid host race, the plant species, and the age of the plant. Differences in the ability of aphids to suppress forisome dispersion may be explained by differences in the composition and quantity of the aphid saliva injected into the plant. Various mechanisms of how pea aphids might suppress forisome dispersion are discussed.
Background
The plant bug, Pachypeltis micranthus Mu et Liu (Hemiptera: Miridae), is an effective potential biological control agent for Mikania micrantha H.B.K. (Asteraceae; one of the most notorious invasive weeds worldwide). However, limited knowledge about this species hindered its practical application and research. Accordingly, we sequenced the genome of this mirid bug, which is of great significance for M. micrantha control.
Results
Here, we generated a 712.72 Mb high-quality chromosome-level assembly of P. micranthus, of which 707.51 Mb (99.27%) of assembled sequences were anchored onto 15 chromosomes with contig N50 of 16.84 Mb. The P. micranthus genome had the highest GC content (42.43%) and the second highest proportion of repetitive sequences (375.82 Mb, 52.73%) than the three other mirid bugs (i.e., Apolygus lucorum, Cyrtorhinus lividipennis, and Nesidiocoris tenuis). Phylogenetic analysis showed that P. micranthus clustered with other mirid bugs and diverged from the common ancestor approximately 200.01 million years ago. We analyzed gene family expansion and or contraction and manually identified some significantly expanded gene families associated with P. micranthus feeding and adaptation to M. micrantha. Compared with the whole body, transcriptome analysis of the salivary gland revealed that most of the upregulated genes were significantly associated with metabolism pathways and peptidase activity, particularly among cysteine peptidase, serine peptidase, and polygalacturonase; this could be one of the reasons for precisely and highly efficient feeding by the oligophagous bug P. micranthus on M. micrantha.
Conclusion
Collectively, this work provides a crucial chromosome-level genome resource to study the evolutionary adaptation between mirid bug and their host. It is also helpful in searching for novel environment-friendly biological strategies to control M. micrantha.
Background
The effect of soil on the plant microbiome is well-studied. However, less is known about the impact of soil microbiome in multitrophic systems. Here we examined the effect of soil on plant and aphid microbiomes, and the reciprocal effect of aphid herbivory on the plant and soil microbiomes. We designed microcosms, which separate below and aboveground compartments, to grow oak seedlings with and without aphid herbivory in soils with three different microbiomes. We used amplicon sequencing and qPCR to characterize the bacterial and fungal communities in soils, phyllospheres, and aphids.
Results
Soil microbiomes significantly affected the microbial communities of phyllospheres and, to a lesser extent, aphid microbiome, indicating plant-mediated assembly processes from soil to aphids via the plant endosphere. While aphid herbivory significantly decreased microbial diversity in phyllospheres independent of soil microbiomes, the effect of aphid herbivory on the community composition in soil varied among the three soils.
Conclusions
This study provides experimental evidence for reciprocal influence of soil, plant and aphid microbiomes, with potential for the development of new microbiome-based pest management strategies.
The emerging elicitor protein PeBL1, extracted from Brevibacillus laterosporus A60, was tested against the potato aphid (Macrosiphum euphorbiae) for its biocontrol potential. Its effects on M. euphorbiae survival, lifespan, immature development, adult reproductive performance, and pest–pathogen interaction were assessed using electrical penetration graphs (EPGs), The levels of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) were significantly increased in the B. laterosporus-treated C. annuum seedlings, indicating substantial accumulation. Brevibacillus laterosporus improved the height of the C. annuum L. plant and the surface structure of the leaves, by reducing M. euphorbiae reproduction and preventing colonization, according to the findings of this study. The activation of pathways was also part of the defensive response (JA, SA, and ET). The use of B. laterosporus for integrated pest management in the agroecosystem appears to be suitable based on these findings against M. euphorbiae.
Aphid (Aphis gossypii Glover) attack frequently results in a significant loss of output and deterioration of fruit quality in cucumber (Cucumis sativus L.). Phloem protein 2 (PP2) is conserved as a phloem lectin in plants, and few studies have been conducted on the regulatory mechanism of PP2. Based on our previous study of CsPP2-A1 in cucumber, to further investigate the biological function of CsPP2-A1, we compared the changes of selectivity, non-selectivity, colonization, reproductions of aphids, and the phenotype in wild type (WT), CsPP2-A1 overexpressing (CsPP2-A1-OE), and CsPP2-A1 interfering (CsPP2-A1-RNAi) cucumber plants after inoculation with aphids. We found that CsPP2-A1-OE cucumber plants generated resistance to aphids. The aphid colonization rate and number of reproductions of CsPP2-A1-OE cucumber plants were significantly lower than that of WT and CsPP2-A1-RNAi cucumber plants. Through Pearson's correlation and principal component analysis (PCA), it was found that CsPP2-A1 played a crucial role in the balance of reactive oxygen species (ROS) in plants. Overexpression of the CsPP2-A1 resulted in increased levels of antioxidant enzyme, eliminating ROS and preventing the damage by ROS in cucumber. Furthermore, nutritional imbalance for aphids and content of secondary metabolites were increased in overexpressed CsPP2-A1 cucumber plants, and thus preventing aphid attack. These together may improve cucumber resistance against aphids and the mechanism of CsPP2-A1 defense against aphids was preliminarily explored.
Aphid salivary effectors play important roles in modulating plant defense responses. The grain aphid Sitobion miscanthi is one of the most economically important cereal aphids worldwide. However, little information is available on the identification and functional analysis of salivary effectors of S. miscanthi. In this study, a candidate salivary effector Sm9723 was identified, which was specifically expressed in aphid salivary glands and highly induced during the aphid feeding phase. Transient overexpression of Sm9723 in Nicotiana benthamiana suppressed BAX and INF1-induced cell death. Further, Sm9723 overexpression inhibited N. benthamiana defense responses by reducing pattern-triggered immunity associated callose deposition and expression levels of jasmonic and salicylic acid-associated defense genes. In addition, the salivary effector Sm9723 of S. miscanthi was effectively silenced through nanocarrier-mediated dsRNA delivery system. After silencing Sm9723, fecundity and survival of S. miscanthi decreased significantly, and the aphid feeding behavior was also negatively affected. These results suggest salivary effector Sm9723 is involved in suppressing plant immunity and is essential in enabling aphid virulence, which could be applied as potential target gene for RNAi-mediated pest control of S. miscanthi.
Among the rice insects, brown planthopper (BPH), (Nilaparvata lugens Stål) is a monophagous migratory phloem-sucking insect causing severe loss in Asiatic countries. High nitrogen and willful insecticide application coupled with an increase in temperature have created havoc by this pest during the last few years in certain parts of India, Indonesia, China, Japan, Taiwan, Vietnam, and the Philippines. Though chemical control measures are advocated to mitigate this insect, yet, the incorporation of host-plant resistance factor is the preferred approach to manage this insect attack owing to the high cost of chemical control and adverse effects on the environment. To date, more than 40 major resistance genes and 22 minor genes or quantitative trait loci (QTLs) are identified. Cloning of 11 BPH resistance genes has been completed to date. Majority of the cloned genes produced coiled-coil nucleotide-binding and leucine-rich repeat protein for the defense response in the host plant. Salicylic acid, jasmonic acid, ethylene, mitogen-activated protein kinases, Ca²⁺, OsRac1, and other signaling molecules play a definite role in the defense response. Signal transduction may lead to sieve tube sealing, production of metabolites, and induction of proteinase inhibitor for defense response against BPH attack. Plants have intrinsic mechanisms for recognition of damage-associated and herbivore-associated molecular patterns and elicitors for host defense response. This review provides an update on the sources of resistance, identification of resistance genes, gene maps, (QTL) detection, cloning, insights into the molecular mechanisms of resistance, and deployment of resistance genes for durable and broad-spectrum resistance in the cultivars against BPH.
One of the best-studied plant chemical defenses is the glucosinolate-myrosinase system found in plants of the family Brassicaceae. There is considerable quantitative and qualitative variation among plant genotypes, tissues, and ontogenetic stages, which poses unique challenges to insect herbivores. Enzyme myrosinase, which is stored in specialized plant cells, hydrolyzes glucosinolates to more toxic isothiocyanates upon tissue disruption. Breakdown of glucosinolates differs depending on the physiological condition of the plant. Glucosinolate hydrolysis products may protect the plant either directly by having an effect on the biology/behavior of insects or indirectly by attracting the pest’s natural enemies. However, a variety of generalist and specialist insect herbivores are known to infest these crops and cause major yield losses. In order to overcome chemical defenses, many insects have developed a number of counteradaptations which function either before or after consumption of food. In this chapter, we have attempted to review these glucosinolate-myrosinase-based defenses and their role in insect-plant interactions.Keywords
Brassica
Mustard oil bombPlant defensePlant secondary metabolitesThioglucosides
The emerging elicitor protein PeBA1, extracted from Bacillus amyloliquefaciens NC6, was tested against the cabbage aphid (Brevicoryne brassicae) for its biocontrol potential. Its effects on the survival, lifespan, immature development, adult reproductive performance, and pest–pathogen interaction were assessed using electrical penetration graphs (EPGs) against B. brassicae. Furthermore, the direct effects of PeBA1 with temperature and climate change in Brassica rapa ssp. Pekinensis plants were investigated by the characterization of active compounds in B. amyloliquefaciens with multi-acting entomopathogenic effects. Compared with controls, PeBA1 treatments decreased (second- and third-generation) B. brassicae population growth rates. In a host selection test, control plants were colonized faster by B. brassicae than PeBA1-treated B. rapa plants. The B. brassicae nymphal development was extended by PeBA1 concentrations. Likewise, fecundity was reduced in PeBA1-treated seedlings compared with control, with fewer offspring produced. The trichomes and wax production on PeBA1-treated leaves resulted in a hostile environment for B. brassicae. PeBA1 altered the surface structure of the leaves, reducing B. brassicae reproduction and preventing colonization. Systemic defensive processes also included the activation of pathways (JA, SA, and ET). Based on these findings against B. brassicae, integrated pest management and bio control with PeBA1 in the agroecosystem appears to be suitable.
Two cryptic species of the Bemisia tabaci species complex, MEAM1 (Middle East-Asia Minor 1) and MED (Mediterranean), are highly destructive herbivores. Attack by herbivorous insects often induces defense responses in plants, including the accumulation of toxic secondary metabolites, the synthesis of herbivore-induced plant volatiles (HIPVs) and defensive proteins, and the release of volatile organic compounds that attract natural enemies. These defense responses, which often differ depending on the herbivore, may affect the preference and performance of later-arriving con- and heterospecific whiteflies that attack the same plant. In the present study, we found that MEAM1 whiteflies preferred settling and ovipositing on non-infested and MED-infested cabbage over MEAM1-infested cabbage plants, but that MED whiteflies showed no significant difference in settling or oviposition preference among non-infested, MEAM1-infested, and MED-infested plants. MEAM1 infestation increased the contents of total phenols and flavonoids in cabbage, which coincided with the increased expression of the following genes in the phenylpropanoid biosynthesis pathway: PAL2, C4H, and 4CL. Soluble protein contents were also markedly higher in the MEAM1-infested cabbage plants than in the non-infested and MED-infested cabbage plants. Overall, these results demonstrate that previous infestation by MEAM1 and MED whiteflies induced defense responses in cabbage plants that had different effects on the host preference and performance of later-arriving con- and heterospecific whiteflies. Phenolic compounds may be the key factors influencing host choice by MEAM1 and MED whiteflies on cabbage plants.
Before the end of the century, atmospheric carbon dioxide levels are predicted to increase to approximately 900 ppm. This will dramatically affect plant physiology and influence environmental interactions and, in particular, plant resistance to biotic stresses. This review is a broad survey of the current research on the effects of elevated CO 2 (eCO 2 ) on phytohormone-mediated resistance of C 3 agricultural crops and related model species to pathogens and insect herbivores. In general, while plants grown in eCO 2 often have increased constitutive and induced salicylic acid levels and suppressed induced jasmonate levels, there are exceptions that implicate other environmental factors, such as light and nitrogen fertilization in modulating these responses. Therefore, this review sets the stage for future studies to delve into understanding the mechanistic basis behind how eCO 2 will affect plant defensive phytohormone signaling pathways under future predicted environmental conditions that could threaten global food security to inform the best agricultural management practices.
[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
The green peach aphid (Myzus persicae Sulzer), a major and harmful chili aphid usually managed using chemical pesticides, is responsible for massive annual agricultural losses. The efficacy of two protein elicitors, PeaT1 and PeBC1, to stimulate a defensive response against M. persicae in chili was studied in this study. When compared to positive (water) and negative (buffer, 50 mM Tris-HCl, pH 8.0) controls, the rates of population growth (intrinsic rate of increase) of M. persicae (second and third generations) were lower with PeaT1- and PeBC1-treated chilli seedlings. M. persicae demonstrated a preference for colonizing control (12.18 ± 0.06) plants over PeaT1- (7.60 ± 0.11) and PeBC1 (6.82 ± 0.09) treated chilli seedlings in a host selection assay. Moreover, PeaT1- and PeBC1-treated chilli seedlings, the nymphal development period of the M. persicae was extended. Similarly, fecundity was lowered in the PeaT1- and PeBC1-treated chilli seedlings, with fewer offspring produced compared to the positive (water) and negative controls (50 mM Tris-HCl, pH 8.0). The trichomes and wax production on the PeaT1 and PeBC1-treated chilli leaves created a disadvantageous surface environment for M. persicae. Compared to control (30.17 ± 0.16 mm−2), PeaT1 (56.23 ± 0.42 mm−2) and PeBC1 (52.14 ± 0.34 mm−2) had more trichomes. The levels of jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) were significantly higher in the PeaT1- and PeBC1-treated chili seedlings, indicating considerable accumulation. PeaT1 and PeBC1 significantly affected the height of the chili plant and the surface structure of the leaves, reducing M. persicae reproduction and preventing colonization, according to the data. The activation of pathways was also part of the defensive response (JA, SA, and ET). This present research findings established an evidence of biocontrol for the utilization of PeaT1 and PeBC1 in the defence of chili plants against M. persicae.
Two cryptic species of the Bemisia tabaci species complex, MEAM1 (Middle East-Asia Minor 1) and MED (Mediterranean), are highly destructive herbivores. Attack by herbivorous insects often induces defense responses in plants, including the accumulation of toxic secondary metabolites, the synthesis of herbivore-induced plant volatiles (HIPVs) and defensive proteins, and the release of volatile organic compounds that attract natural enemies. These defense responses, which often differ depending on the herbivore, may affect the preference and performance of later-arriving con- and heterospecific whiteflies that attack the same plant. In the present study, we found that MEAM1 whiteflies preferred settling and ovipositing on non-infested and MED-infested cabbage over MEAM1-infested cabbage plants, but that MED whiteflies showed no significant difference in settling or oviposition preference among non-infested, MEAM1-infested, and MED-infested plants. MEAM1 infestation increased the contents of total phenols and flavonoids in cabbage, which coincided with the increased expression of the following genes in the phenylpropanoid biosynthesis pathway: PAL2 , C4H , and 4CL1 . Soluble protein contents were also markedly higher in the MEAM1-infested cabbage plants than in the non-infested and MED-infested cabbage plants. Overall, these results demonstrate that previous infestation by MEAM1 and MED whiteflies induced defense responses in cabbage plants that had different effects on the host preference and performance of later-arriving con- and heterospecific whiteflies. Phenolic compounds may be the key factors influencing host choice by MEAM1 and MED whiteflies on cabbage plants.
We have previously demonstrated that Arabidopsis (Arabidopsis thaliana) phloem protein PP2-A1 is an integral component of resistance to the green peach aphid (Myzus persicae). Here, we report that M. persicae overcomes the resistance of PP2-A1 by using the salivary protein Mp1 as an energetic effector and an interactor of AtPP2-A1. Using the RNA interference technique, we demonstrated that Mp1 plays an essential role in the phloem-feeding activity of M. persicae. When the Mp1 gene was silenced, aphids incurred serious impairments not only in phloem-feeding activity, but also in survival and fertility. In essence, phloem-feeding activity was attributed to the molecular interaction between Mp1 and AtPP2-A1. The Mp1 and AtPP2-A1 interactions were localized to plant cell membranes by co-immunoprecipitation and bimolecular fluorescence complementation experiments. Furthermore, the interaction was found to be required for aphid feeding on Arabidopsis phloem. Overall, our results suggest that Mp1 is an important effector of M. persicae and interacts with AtPP2-A1 to facilitate infestation in the plant tissue by this insect.
Plants have the ability to detect and respond to biotic stresses. They contain pattern recognition receptors (PRRs) that specifically recognize conserved molecules from their enemies and activate immune responses. In this review, I discuss recent efforts to discover PRRs for herbivory-associated cues that originate from oral secretions, eggs, damaged plant cells or secondary endogenous signals. Although several potential PRRs have been identified and shown to confer resistance to insects, proof of direct binding to a ligand is scarce and there are still many uncharacterized ligand-receptor pairs. However, several studies suggest that, like for microbial pathogens, plants use similar PRR complexes to detect herbivory.
Herbivores and insects are diverse living organisms with millions of species
around the globe. These insects and herbivores require an adequate amount
of food and nutrients to fulfil their need to live. Plants are the major source
that provides nutrient and food supply to these insects and herbivores. Plants
live with insects and herbivores together in an ecosystem since very long from
350 million years. Biological control is widely known to be the use of living
organism’s population to suppress the other population of living organisms.
Plant insect and herbivore interaction is mediated by microbes that alter
various aspects of plant community and result to structure plant communities.
Recently molecular tools showed a very diverse nature of microbiota related
to insects. Plants have adopted several strategies against insects and herbivores
ranging from a morphological defence that activate plant immune system.
There are many biological agents used in insect pest management (IPM)
which include fungi, bacteria, virus, protozoans, botanicals (plants or products
derived from plants), predator/pathogen system, plant-incorporated protectants
(PIPs) and insect pheromones. Plant defence, morphology and physiology
against herbivorous insects are mediated by plant hormones especially
cytokinins and insect symbionts. In addition to insect symbionts, plant traits
like a physical barrier, mass flowering or fruiting can alter the performance of
herbivores and insects. There are positive effects of mycorrhizal fungal-plant-
insect
interaction, and insects and microorganisms have a greater role in plant
productivity, nutrient recycling and plant community structure. Apart from
fungi, plant-insect interaction is also affected by bacteria. Recent advances
revealed that plant has adopted certain mechanism like plant defence theory
to defend themselves from insect herbivores. Furthermore, climate change
has also affected plant-herbivore interaction. DNA metabarcoding technique
helped to accurately measure herbivore diet. Plants use different proteins and
secondary metabolites (terpenes, phenolic compounds, sulphur) against insect
herbivores. Also, to plant secondary metabolites, microorganisms have also a
role in mediating plant defences against insects and herbivores.
Plants possess their own defence mechanisms to combat infestations of herbivorous insects and pathogens. It has few preexisting defence mechanisms, whereas most of the defence response is activated only after insect or pathogen invasion. Crosstalk between defence signalling pathways induced in response to herbivore/pathogen attack offer plants to regulate defence mechanism in an effective manner. Crosstalk and interaction of signalling pathways can function synergistically, or either one is suppressed under stress condition. Crosstalk enables the plant to utilize less energy for defence response and allocate energy for its growth and development. Host plant resistance against herbivores can be manipulated using chemical elicitors, which induces defence signalling mechanism in plants. Unravelling of defence mechanisms and phytohormonal signalling pathway under stress condition, the induced responses of the herbivores can be predicted, that can be further utilized for pest management and reduction in crop losses.
Important theories that define the role of secondary metabolites in the co‐evolution of plants and insect herbivores were proposed in a series of publications in the 1950s and 1960s. Now, roughly 50 years later, it is possible to revisit these early theories and determine how well they hold up in the light of sequenced genomes, molecular phylogenies, completely elucidated biosynthetic pathways and evidence for specific biochemical detoxification mechanisms in insect herbivores. Two classes of plant secondary metabolites stand out as being particularly well‐studied: the glucosinolates, which are characteristic of cruciferous plants; and the benzoxazinoids, which are found in many grass species. Using these metabolic pathways as examples, it is possible to demonstrate at the molecular level how biosynthesis of plant secondary metabolites evolved from primary metabolism, how the development of defensive chemicals can drive plant‐herbivore co‐evolution and how insects are able to respond to plant defences at the molecular level.
ADDITIONAL INDEX WORDS. Aphis gossypii, Cucumis melo, insect, phloem, NBS-LRR ABSTRACT. Resistance to cotton-melon aphid (Aphis gossypii Glover) segregated as a single dominant gene in a melon (Cucumis melo L.) mapping population derived from the cross 'Top Mark' x PI 414723. Sixty-four F2-derived F3 families were used to map the aphid resistance locus, Vat, with respect to randomly amplified polymorphic DNA (RAPD) and restriction fragment length polymorphism (RFLP) markers. RFLP markers NBS-2 and AC-39 flanked Vat at distances of 3.1 cM and 6.4 cM, respectively. NBS-2 is homologous to the nucleotide binding site-leucine-rich repeat (NBS-LRR) superfamily of plant resistance genes. Another homolog of this superfamily, NBS-5, was positioned ≈16.8 cM from Vat, raising the possibility that Vat resides in a cluster of NBS-LRR paralogs. RFLP marker AC-8, which has similarity to plant lipoxygenases, was positioned at ≈5.5 cM from Vat. Monogenic resistance to A. gossypii has been identified in two sources of melon germplasm, Indian accession PI 371795 (progenitor of PI 414723) and Korean accession PI 161375. To test for an allelic relation between the genes controlling aphid resistance in these two distinct germplasm sources, melon plants of a backcross population from a cross between two resistant lines having Indian- or Korean-derived resistance were infested with aphids. At least 90 out of 92 segregating progeny were aphid resistant, suggesting that the same resistance gene, Vat, is present in both sources of melon germplasm.
The compoundN-(17-hydroxylinolenoyl)-l-glutamine (named here volicitin) was isolated from oral secretions of beet armyworm caterpillars. When applied to damaged
leaves of corn seedlings, volicitin induces the seedlings to emit volatile compounds that attract parasitic wasps, natural
enemies of the caterpillars. Mechanical damage of the leaves, without application of this compound, did not trigger release
of the same blend of volatiles. Volicitin is a key component in a chain of chemical signals and biochemical processes that
regulate tritrophic interactions among plants, insect herbivores, and natural enemies of the herbivores.
The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious economic pest of wheat and barley in North America, South America, and South Africa. Using aphid-resistant
cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in wheat,
Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accelerated through
the use of molecular markers. DNA of wheat from near-isogenic lines and segregating F2 populations was amplified with microsatellite primers via PCR. Results revealed that the locus for wheat microsatellite GWM111
(Xgwm111), located on wheat chromosome 7DS (short arm), is tightly linked to Dn1, Dn2 and Dn5, as well as Dnx in PI 220127. Segregation data indicate RWA resistance in wheat PI 220127 is also conferred by a single dominant resistance
gene (Dnx). These results confirm that Dn1, Dn2 and Dn5 are tightly linked to each other, and provide new information about their location, being 7DS, near the centromere, instead
of as previously reported on 7DL. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated
as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locations of markers and the linked genes were
confirmed by di-telosomic and nulli-tetrasomic analyses. Genetic linkage maps of the above RWA resistance genes and markers
have been constructed for wheat chromosomes 1D and 7D. These markers will be useful in marker-assisted breeding for RWA-resistant
wheat.
Abstract Injection of siRNA (small interfering RNA) into parthenogenetic adult pea aphids (Acyrthosiphon pisum) is shown here to lead to depletion of a target salivary gland transcript. The siRNA was generated from double stranded RNA that covered most of the open reading frame of the transcript, which we have called Coo2. The Coo2 transcript level decreases dramatically over a 3-day period after injection of siRNA. With a lag of 1 to 2 days, the siCoo2-RNA injected insects died, on average 8 days before the death of control insects injected with siRNA for green fluorescent protein. It appears, therefore, that siRNA injections into adults will be a useful tool in studying the roles of individual transcripts in aphid salivary glands and suggests that siCoo2-RNA injections can be a useful positive control in such studies.
In many insects the first abdominal segment possesses embryonic appendages called pleuropodia. Here we show the embryogenesis of pleuropodial cells of the periodical cicada, Magicicada cassini (Fisher 1851) (Insecta, Homoptera, Cicadidae). An antibody, anti-horseradish perioxidase (HRP), that is usually neuron-specific strongly marked the pleuropodial anlagen and revealed their ectodermal origin shortly after limb bud formation. Thereafter the cells sank into the epidermis and their apical parts enlarged. A globular part protruded from the body wall. Filamentous structures were marked at the stem region and into the apical dilation. In later embryonic stages the pleuropodia degenerated. Despite the binding of anti-HRP the cells had no morphological neuronal characters and cannot be regarded as neurons. The binding indicates that glycosylated cell surface molecules contribute to the adhesion between the presumably glandular pleuropodial cells. In comparison, anti-HRP does not mark the pleuropodia of Orthoptera.
Nine proteins secreted in the saliva of the pea aphid Acyrthosiphon pisum were identified by a proteomics approach using GE-LC-MS/MS and LC-MS/MS, with reference to EST and genomic sequence data for A. pisum. Four proteins were identified by their sequences: a homolog of angiotensin-converting enzyme (an M2 metalloprotease), an M1 zinc-dependant metalloprotease, a glucose-methanol-choline (GMC)-oxidoreductase and a homolog to regucalcin (also known as senescence marker protein 30). The other five proteins are not homologous to any previously described sequence and included an abundant salivary protein (represented by ACYPI009881), with a predicted length of 1161 amino acids and high serine, tyrosine and cysteine content. A. pisum feeds on plant phloem sap and the metalloproteases and regucalcin (a putative calcium-binding protein) are predicted determinants of sustained feeding, by inactivation of plant protein defences and inhibition of calcium-mediated occlusion of phloem sieve elements, respectively. The amino acid composition of ACYPI009881 suggests a role in the aphid salivary sheath that protects the aphid mouthparts from plant defences, and the oxidoreductase may promote gelling of the sheath protein or mediate oxidative detoxification of plant allelochemicals. Further salivary proteins are expected to be identified as more sensitive MS technologies are developed.
Glucosinolates are defensive secondary compounds that display large structural diversity in Arabidopsis thaliana and related plants. Much attention has been paid to variation in the biosynthesis of Met-derived aliphatic glucosinolates and its ecological consequences, but little is known about the genes that cause qualitative and quantitative differences in Trp-derived indole glucosinolates. We use a combination of quantitative trait locus (QTL) fine-mapping and microarray-based transcript profiling to identify CYP81F2 (At5g57220), encoding a cytochrome P450 monooxygenase, as the gene underlying Indole Glucosinolate Modifier1 (IGM1), a metabolic QTL for the accumulation of two modified indole glucosinolates, 4-hydroxy-indole-3-yl-methyl and 4-methoxy-indole-3-yl-methyl glucosinolate. We verify CYP81F2 function with two SALK T-DNA insertion lines and show that CYP81F2 catalyzes the conversion of indole-3-yl-methyl to 4-hydroxy-indole-3-yl-methyl glucosinolate. We further show that the IGM1 QTL is largely caused by differences in CYP81F2 expression, which results from a combination of cis- and trans-acting expression QTL different from known regulators of indole glucosinolate biosynthesis. Finally, we elucidate a potential function of CYP81F2 in plant-insect interactions and find that CYP81F2 contributes to defense against the green peach aphid (Myzus persicae) but not to resistance against herbivory by larvae from four lepidopteran species.
Selection pressure exerted by insects and microorganisms shapes the diversity of plant secondary metabolites. We identified a metabolic pathway for glucosinolates, known insect deterrents, that differs from the pathway activated by chewing insects. This pathway is active in living plant cells, may contribute to glucosinolate turnover, and has been recruited for broad-spectrum antifungal defense responses. The Arabidopsis CYP81F2 gene encodes a P450 monooxygenase that is essential for the pathogen-induced accumulation of 4-methoxyindol-3-ylmethylglucosinolate, which in turn is activated by the atypical PEN2 myrosinase (a type of beta-thioglucoside glucohydrolase) for antifungal defense. We propose that reiterated enzymatic cycles, controlling the generation of toxic molecules and their detoxification, enable the recruitment of glucosinolates in defense responses.
We have assessed ultraviolet-B (UV-B)-induced injury in wild-type Arabidopsis thaliana and two mutants with altered aromatic secondary product biosynthesis. Arabidopsis mutants defective in the ability to synthesize UV-B-absorbing compounds (flavonoids in transparent testa 5 [tt5] and sinapate esters in ferulic acid hydroxylase 1 [fah1]) are more sensitive to UV-B than is the wild-type Landsberg erecta. Despite its ability to accumulate UV-absorptive flavonoid compounds, the ferulic acid hydroxylase mutant fah1 exhibits more physiological injury (growth inhibition and foliar lesions) than either wild type or tt5. The extreme UV-B sensitivity of fah1 demonstrates the importance of hydroxycinnamate esters as UV-B protectants. Consistent with the whole-plant response, the highest levels of lipid and protein oxidation products were seen in fah1. Ascorbate peroxidase enzyme activity was also increased in the leaves of UV-B-treated plants in a dose- and genotype-dependent manner. These results demonstrate that, in A. thaliana, hydroxycinnamates are more effective UV-B protectants than flavonoids. The data also indicate that A. thaliana responds to UV-B as an oxidative stress, and sunscreen compounds reduce the oxidative damage caused by UV-B.
Resistance against the aphid Macrosiphum euphorbiae previously was observed in tomato and attributed to a novel gene, designated Meu-1, tightly linked to the nematode resistance gene, Mi. Recent cloning of Mi allowed us to determine whether Meu-1 and Mi are the same gene. We show that Mi is expressed in leaves, that aphid resistance is isolate-specific, and that susceptible tomato transformed with Mi is resistant to the same aphid isolates as the original resistant lines. We conclude that Mi and Meu-1 are the same gene and that Mi mediates resistance against both aphids and nematodes, organisms belonging to different phyla. Mi is the first example of a plant resistance gene active against two such distantly related organisms. Furthermore, it is the first isolate-specific insect resistance gene to be cloned and belongs to the nucleotide-binding, leucine-rich repeat family of resistance genes.
The Mi locus of tomato confers resistance to root knot nematodes. Tomato DNA spanning the locus was isolated as bacterial artificial chromosome clones, and 52 kb of contiguous DNA was sequenced. Three open reading frames were identified with similarity to cloned plant disease resistance genes. Two of them, Mi-1.1 and Mi-1.2, appear to be intact genes; the third is a pseudogene. A 4-kb mRNA hybridizing with these genes is present in tomato roots. Complementation studies using cloned copies of Mi-1.1 and Mi-1.2 indicated that Mi-1.2, but not Mi-1.1, is sufficient to confer resistance to a susceptible tomato line with the progeny of transformants segregating for resistance. The cloned gene most similar to Mi-1.2 is Prf, a tomato gene required for resistance to Pseudomonas syringae. Prf and Mi-1.2 share several structural motifs, including a nucleotide binding site and a leucine-rich repeat region, that are characteristic of a family of plant proteins, including several that are required for resistance against viruses, bacteria, fungi, and now, nematodes.
Phytoalexins are low molecular weight antimicrobial compounds that are synthesized in response to pathogen attack. The phytoalexin camalexin, an indole derivative, is produced by Arabidopsis in response to infection with the bacterial pathogen Pseudomonas syringae. The phytoalexin deficient 3 (pad3) mutation, which causes a defect in camalexin production, has no effect on resistance to P. syringae but compromises resistance to the fungal pathogen Alternaria brassicicola. We have now isolated PAD3 by map-based cloning. The predicted PAD3 protein appears to be a cytochrome P450 monooxygenase, similar to those from maize that catalyze synthesis of the indole-derived secondary metabolite 2,4-dihydroxy-1, 4-benzoxazin-3-one. The expression of PAD3 is tightly correlated with camalexin synthesis and is regulated by PAD4 and PAD1. On the basis of these findings, we conclude that PAD3 almost certainly encodes an enzyme required for camalexin biosynthesis. Moreover, these results strongly support the idea that camalexin does not play a major role in plant resistance to P. syringae infection, although it is involved in resistance to a fungal pathogen.
Little is known about molecular responses in plants to phloem feeding by insects. The induction of genes associated with wound and pathogen response pathways was investigated following green peach aphid (Myzus persicae) feeding on Arabidopsis. Aphid feeding on rosette leaves induced transcription of two genes associated with salicylic acid (SA)-dependent responses to pathogens (PR-1 and BGL2) 10- and 23-fold, respectively. Induction of PR-1 and BGL2 mRNA was reduced in npr1 mutant plants, which are deficient in SA signaling. Application of the SA analog benzothiadiazole led to decreases in aphid reproduction on leaves of both wild-type plants and mutant plants deficient in responsiveness to SA, suggesting that wild-type SA-dependent responses do not influence resistance to aphids. Two-fold increases occurred in mRNA levels of PDF1.2, which encodes defensin, a peptide involved in the jasmonate (JA)-/ethylene-dependent response pathway. Transcripts encoding JA-inducible lipoxygenase (LOX2) and SA/JA-inducible Phe-ammonia lyase increased 1.5- to 2-fold. PDF1.2 and LOX2 induction by aphids did not occur in infested leaves of the JA-resistant coi1-1 mutant. Aphid feeding induced 10-fold increases in mRNA levels of a stress-related monosaccharide symporter gene, STP4. Phloem feeding on Arabidopsis leads to stimulation of response pathways associated with both pathogen infection and wounding.
Feeding by the tobacco specialist Manduca sexta (Lepidoptera, Sphingidae) and application of larval oral secretions and regurgitant (R) to mechanical wounds are known to elicit: (a) a systemic release of mono- and sesquiterpenes, (b) a jasmonate burst, and (c) R-specific changes in transcript accumulation of putatively growth- and defense-related mRNAs in Nicotiana attenuata Torr. ex Wats. We identified several fatty acid-amino acid conjugates (FACs) in the R of M. sexta and the closely related species Manduca quinquemaculata which, when synthesized and applied to mechanical wounds at concentrations comparable with those found in R, elicited all three R-specific responses. Ion-exchange treatment of R, which removed all detectable FACs and free fatty acids (FAs), also removed all detectable activity. The biological activity of ion-exchanged R could be completely restored by the addition of synthetic FACs at R-equivalent concentrations, whereas the addition of FAs did not restore the biological activity of R. We conclude that the biological activity of R is not related to the supply of FAs to the octadecanoid cascade for endogenous jasmonate biosynthesis, but that FACs elicit the herbivore-specific responses by another mechanism and that the insect-produced modification of plant-derived FAs is necessary for the plant's recognition of this specialized herbivore.
The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a serious economic pest of wheat worldwide. Host plant resistance is the preferred method to control RWA infestations. The identification and mapping of RWA-resistant genes and the development of resistant wheat cultivars can be facilitated through the use of molecular markers. In the present study, microsatellite (SSR) markers linked to the RWA-resistant genes Dn4 and Dn6 were identified using several F(2) mapping populations derived from crosses of susceptible wheat cultivars and resistant sources. Two flanking microsatellite markers Xgwm106 and Xgwm337 are linked in coupling phase with Dn4 on the short arm of wheat chromosome 1D at 7.4 cM and 12.9 cM, respectively. Two other microsatellite markers Xgwm44 and Xgwm111 are linked to Dn6 in coupling phase near the centromere on the short arm of chromosome 7D at 14.6 cM and 3.0 cM, respectively. This is the first report on the chromosomal location of Dn6, which proved to be either allelic or tightly linked to Dn1, Dn2 and Dn5. This result of Dn6 location contradicts previous reports that Dn6 was independent of Dn1, Dn2 and Dn5. The linked markers can be conveniently used for marker-assisted selection in wheat breeding programs for the identification and/or pyramiding of Dn4 and Dn6 genes.
The tomato gene Mi-1.2 confers resistance against root-knot nematodes and some isolates of potato aphid. Resistance to the whitefly Bemisia tabaci previously has been observed in Mi-bearing commercial tomato cultivars, suggesting that Mi, or a closely linked gene, is responsible for the resistance. The response of two biotypes of B. tabaci to tomato carrying the cloned Mi was compared with that of the isogenic untransformed tomato line Moneymaker. Our results indicate that Mi-1.2 is responsible for the resistance in tomato plants to both B- and Q- biotypes. Mi-1.2 is unique among characterized resistance genes in its activity against three very different organisms (root-knot nematodes, aphids, and whiteflies). These pests are among the most important on tomato crops worldwide, making Mi a valuable resource in integrated pest management programs.
We experimentally reanalyzed the classic interaction between Pieris rapae, a specialist lepidopteran herbivore, and isothiocyanates (mustard oils) that are characteristic phytochemicals of the Brassicaceae. Previous investigations have suggested that P. rapae is unaffected by isothiocyanates. Using whole plants, root extracts, and a microencapsulated formulation of allyl isothiocyanate, we now show that isothiocyanates reduce herbivore survival and growth, and increase development time, each in a dose-dependent manner. Neither the substrate allyl glucosinolate, nor myrosinase, the enzyme that results in the breakdown of glucosinolates, negatively affected P. rapae. Thus, we present strong evidence for a role for isothiocyanates in plant resistance against the specialist herbivore P. rapae.
Controlled vocabularies are increasingly used by databases to describe genes and gene products because they facilitate identification of similar genes within an organism or among different organisms. One of The Arabidopsis Information Resource's goals is to associate all Arabidopsis genes with terms developed by the Gene Ontology Consortium that describe the molecular function, biological process, and subcellular location of a gene product. We have also developed terms describing Arabidopsis anatomy and developmental stages and use these to annotate published gene expression data. As of March 2004, we used computational and manual annotation methods to make 85,666 annotations representing 26,624 unique loci. We focus on associating genes to controlled vocabulary terms based on experimental data from the literature and use The Arabidopsis Information Resource-developed PubSearch software to facilitate this process. Each annotation is tagged with a combination of evidence codes, evidence descriptions, and references that provide a robust means to assess data quality. Annotation of all Arabidopsis genes will allow quantitative comparisons between sets of genes derived from sources such as microarray experiments. The Arabidopsis annotation data will also facilitate annotation of newly sequenced plant genomes by using sequence similarity to transfer annotations to homologous genes. In addition, complete and up-to-date annotations will make unknown genes easy to identify and target for experimentation. Here, we describe the process of Arabidopsis functional annotation using a variety of data sources and illustrate several ways in which this information can be accessed and used to infer knowledge about Arabidopsis and other plant species.
In plants, Glycoside Hydrolase (GH) Family 1 beta -glycosidases are believed to play important roles in many diverse processes including chemical defense against herbivory, lignification, hydrolysis of cell wall-derived oligosaccharides during germination, and control of active phytohormone levels. Completion of the Arabidopsis thaliana genome sequencing project has enabled us, for the first time, to determine the total number of Family 1 members in a higher plant. Reiterative database searches revealed a multigene family of 48 members that includes eight probable pseudogenes. Manual reannotation and analysis of the entire family were undertaken to rectify existing misannotations and identify phylogenetic relationships among family members. Forty-seven members (designated BGLU1 through BGLU47 ) share a common evolutionary origin and were subdivided into approximately 10 subfamilies based on phylogenetic analysis and consideration of intron-exon organizations. The forty-eighth member of this family ( At3g06510; sfr2 ) is a beta -glucosidase-like gene that belongs to a distinct lineage. Information pertaining to expression patterns and potential functions of Arabidopsis GH Family 1 members is presented. To determine the biological function of all family members, we intend to investigate the substrate specificity of each mature hydrolase after its heterologous expression in the Pichia pastoris expression system. To test the validity of this approach, the BGLU44 -encoded hydrolase was expressed in P. pastoris and purified to homogeneity. When tested against a wide range of natural and synthetic substrates, this enzyme showed a preference for beta -mannosides including 1,4- beta -D-mannooligosaccharides, suggesting that it may be involved in A. thaliana in degradation of mannans, galactomannans, or glucogalactomannans. Supporting this notion, BGLU44 shared high sequence identity and similar gene organization with tomato endosperm beta -mannosidase and barley seed beta -glucosidase/ beta -mannosidase BGQ60.
Aphids and related insects feed from a single cell type in plants: the phloem sieve element. Genetic resistance to Acyrthosiphon kondoi Shinji (bluegreen aphid or blue alfalfa aphid) has been identified in Medicago truncatula Gaert. (barrel medic) and backcrossed into susceptible cultivars. The status of M. truncatula as a model legume allows an in-depth study of defense against this aphid at physiological, biochemical, and molecular levels. In this study, two closely related resistant and susceptible genotypes were used to characterize the aphid-resistance phenotype. Resistance conditions antixenosis since migratory aphids were deterred from settling on resistant plants within 6 h of release, preferring to settle on susceptible plants. Analysis of feeding behavior revealed the trait affects A. kondoi at the level of the phloem sieve element. Aphid reproduction on excised shoots demonstrated that resistance requires an intact plant. Antibiosis against A. kondoi is enhanced by prior infestation, indicating induction of this phloem-specific defense. Resistance segregates as a single dominant gene, AKR (Acyrthosiphon kondoi resistance), in two mapping populations, which have been used to map the locus to a region flanked by resistance gene analogs predicted to encode the CC-NBS-LRR subfamily of resistance proteins. This work provides the basis for future molecular analysis of defense against phloem parasitism in a plant model system.
Plant defenses against pathogens and insects are regulated differentially by cross-communicating signaling pathways in which salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) play key roles. To understand how plants integrate pathogen- and insect-induced signals into specific defense responses, we monitored the dynamics of SA, JA, and ET signaling in Arabidopsis after attack by a set of microbial pathogens and herbivorous insects with different modes of attack. Arabidopsis plants were exposed to a pathogenic leaf bacterium (Pseudomonas syringae pv. tomato), a pathogenic leaf fungus (Alternaria brassicicola), tissue-chewing caterpillars (Pieris rapae), cell-content-feeding thrips (Frankliniella occidentalis), or phloem-feeding aphids (Myzus persicae). Monitoring the signal signature in each plant-attacker combination showed that the kinetics of SA, JA, and ET production varies greatly in both quantity and timing. Analysis of global gene expression profiles demonstrated that the signal signature characteristic of each Arabidopsis-attacker combination is orchestrated into a surprisingly complex set of transcriptional alterations in which, in all cases, stress-related genes are overrepresented. Comparison of the transcript profiles revealed that consistent changes induced by pathogens and insects with very different modes of attack can show considerable overlap. Of all consistent changes induced by A. brassicicola, Pieris rapae, and E occidentalis, more than 50% also were induced consistently by P. syringae. Notably, although these four attackers all stimulated JA biosynthesis, the majority of the changes in JA-responsive gene expression were attacker specific. All together, our study shows that SA, JA, and ET play a primary role in the orchestration of the plant's defense response, but other regulatory mechanisms, such as pathway cross-talk or additional attacker-induced signals, eventually shape the highly complex attacker-specific defense response.
Aphids, which are phloem-feeding insects, cause extensive loss of plant productivity and are vectors of plant viruses. Aphid feeding causes changes in resource allocation in the host, resulting in an increase in flow of nutrients to the insect-infested tissue. We hypothesized that leaf senescence, which is involved in the programmed degradation of cellular components and the export of nutrients out of the senescing leaf, could be utilized by plants to limit aphid growth. Using Arabidopsis (Arabidopsis thaliana) and green peach aphid (GPA; Myzus persicae Sulzer), we found that GPA feeding induced premature chlorosis and cell death, and increased the expression of SENESCENCE ASSOCIATED GENES (SAGs), all hallmarks of leaf senescence. Hypersenescence was accompanied by enhanced resistance against GPA in the Arabidopsis constitutive expresser of PR genes5 and suppressor of SA insensitivity2 mutant plants. In contrast, resistance against GPA was compromised in the phytoalexin deficient4 (pad4) mutant plant. The PAD4 gene, which is expressed at elevated level in response to GPA feeding, modulates the GPA feeding-induced leaf senescence. In comparison to the wild-type plant, GPA feeding-induced chlorophyll loss, cell death, and SAG expression were delayed in the pad4 mutant. Although PAD4 is associated with camalexin synthesis and salicylic acid (SA) signaling, camalexin and SA signaling are not important for restricting GPA growth; growth of GPA on the camalexin-biosynthesis mutant, pad3, and the SA deficient2 and NahG plants and the SA-signaling mutant, nonexpresser of PR genes1, were comparable to that on the wild-type plant. Our results suggest that PAD4 modulates the activation of senescence in the aphid-infested leaves, which contributes to basal resistance to GPA.
Successful phloem feeding requires overcoming a number of phloem-related plant properties and reactions. The most important
hurdle is formed by the phloem wound responses, such as coagulating proteins in the phloem sieve elements of the plant and
in the capillary food canal in the insect's mouth parts, i.e. the stylets. It seems that in order to prevent protein clogging
inside a sieve element, ejection of watery saliva plays an important role. This ejection is detected in the electrical penetration
graph (EPG) as E1 salivation and always precedes phloem sap ingestion. During this feeding from sieve elements, another regular
and concurrent salivation also occurs, the watery E2 salivation. This E2 saliva is added to the ingested sap and, it probably
prevents phloem proteins from clogging inside the capillary food canal. Whatever the biochemical mode of action of the inhibition
of protein coagulation might be, in some plants aphids do not seem to be able to prevent clogging, which may explain the resistance
to aphids in these plants. The relevance of this hypothesis is demonstrated by new experimental results and is related to
new EPG results from plants with phloem-located resistance.
Aphids feed from sieve tubes deep inside the host plant. Therefore, aphids must be able to recognize their host plant(s) and
to direct their stylets which must be long and thin enough to reach and puncture the sieve tubes at a particular site. Sieve
tubes in angiosperms are longitudinal arrays of sieve element/companion cell modules which are highly sensitive to disturbance
of any kind. The sieve tubes dispose of elaborate sealing mechanisms such as protein plugging and callose sealing which are
triggered by a rise in calcium in the sieve tubes. Aphids seem to have developed a range of physical and chemical measures
to limit the amount of calcium influx in response to stylet puncturing. Loss of sieve-element turgor pressure induced by stylet
insertion is minimized by the minute stylet volume. Turgor-dependent Ca2+ influx, possibly mediated by mechano sensitive Ca2+ channels, must therefore be limited. The components of the sheath and watery saliva play a pivotal role in establishing the
physical and chemical constraints on the rise of calcium. Most likely, sheath saliva prevents the influx of calcium from the
apoplast by sealing the stylet puncture site while watery saliva may prevent plugging and sealing of sieve plates by potential
interaction with SE sap ingredients.
Plants can perceive a wide range of biotic attackers and respond with targeted induced defenses. Specificity in plant non-self-recognition occurs either directly by perception of pest-derived elicitors or indirectly through resistance protein recognition of host targets that are inappropriately proteolyzed. Indirect plant perception can occur during interactions with pathogens, yet evidence for analogous events mediating the detection of insect herbivores remains elusive. Here we report indirect perception of herbivory in cowpea (Vigna unguiculata) plants attacked by fall armyworm (Spodoptera frugiperda) larvae. We isolated and identified a disulfide-bridged peptide (⁺ICDINGVCVDA⁻), termed inceptin, from S. frugiperda larval oral secretions that promotes cowpea ethylene production at 1 fmol leaf⁻¹ and triggers increases in the defense-related phytohormones salicylic acid and jasmonic acid. Inceptins are proteolytic fragments of chloroplastic ATP synthase γ-subunit regulatory regions that mediate plant perception of herbivory through the induction of volatile, phenylpropanoid, and protease inhibitor defenses. Only S. frugiperda larvae that previously ingested chloroplastic ATP synthase γ-subunit proteins and produced inceptins significantly induced cowpea defenses after herbivory. Digestive fragments of an ancient and essential plant enzyme, inceptin functions as a potent indirect signal initiating specific plant responses to insect attack.
• elicitor
• guard hypothesis
• indirect perception
• insect herbivory
• plant defense
Camalexin represents the main phytoalexin in Arabidopsis (Arabidopsis thaliana). The camalexin-deficient phytoalexin deficient 3 (pad3) mutant has been widely used to assess the biological role of camalexin, although the exact substrate of the cytochrome P450 enzyme 71B15 encoded by PAD3 remained elusive. 2-(Indol-3-yl)-4,5-dihydro-1,3-thiazole-4-carboxylic acid (dihydrocamalexic acid) was identified as likely intermediate in camalexin biosynthesis downstream of indole-3-acetaldoxime, as it accumulated in leaves of silver nitrate-induced pad3 mutant plants and it complemented the camalexin-deficient phenotype of a cyp79b2/cyp79b3 double-knockout mutant. Recombinant CYP71B15 heterologously expressed in yeast catalyzed the conversion of dihydrocamalexic acid to camalexin with preference of the (S)-enantiomer. Arabidopsis microsomes isolated from leaves of CYP71B15-overexpressing and induced wild-type plants were capable of the same reaction but not microsomes from induced leaves of pad3 mutants. In conclusion, CYP71B15 catalyzes the final step in camalexin biosynthesis.
Designing PCR and sequencing primers are essential activities for molecular biologists around the world. This chapter assumes acquaintance with the principles and practice of PCR, as outlined in, for example, refs. 1, 2, 3, 4.
Within the Aphidoidea, most species of Aphididae, as long as they are in small numbers and not carrying plant viruses, do little perceptible damage to their food plants. In species that cause toxicoses, it is usually assumed that some component of the saliva must be responsible. Paradoxically, however, the salivary enzymes of Aphididae are similar to those that already occur in plants-oxidases and enzymes that depolymerize polysaccharides-and the salivary enzymes are injected in very small amounts relative to their counterparts in the plant. Damage to plants triggers defensive, biochemical responses, and it is suggested that the injected enzymes serve mainly to divert or counter responses at the immediate interface of stylets and plant tissues. The saliva of Aphididae contains non-enzymic, reducing compounds which, in the presence of oxidases, can combine with and inactivate defensive phytochemicals-including those released in response to damage and transported in the phloem sieve tube sap on which Aphididae feed. Salivary and gut oxidases deactivate ingested phytochemicals by oxidative polymerization. Aphididae inject saliva into sieve tubes before sustained ingestion of sap, and this saliva has been presumed to condition the sieve tubes, but in what way remains unclear. It is suggested that there is a dynamic biochemical interaction between aphids and plants; that the interaction is usually well balanced for most of the Aphididae; hence, no outcome is readily observable. Where a significant imbalance occurs, however, either the aphid is unable to feed, i.e. the plant is resistant, and/or the aphid does not effectively counter a hypersensitive response. Not all plant responses are disadvantageous to aphids. Gall-forming Aphidoidea trigger and control abnormal growth in the plant to the insects' advantage, possibly by eliciting vigorous oxidation in selective meristematic tissues, thereby limiting supply of molecular oxygen and inhibiting oxygen-dependent growth-controls. Current problems and possible approaches for further research are reviewed.
Phytoalexins are low molecular weight antimicrobial compounds that are synthesized in response to pathogen attack. The phytoalexin camalexin, an indole derivative, is produced by Arabidopsis in response to infection with the bacterial pathogen Pseudomonas syringae. The phytoalexin deficient 3 (pad3) mutation, which causes a defect in camalexin production, has no effect on resistance to P. syringae but compromises resistance to the fungal pathogen Alternaria brassicicola. We have now isolated PAD3 by map-based cloning. The predicted PAD3 protein appears to be a cytochrome P450 monooxygenase, similar to those from maize that catalyze synthesis of the indole-derived secondary metabolite 2,4-dihydroxy-1,4-benzoxazin-3-one. The expression of PAD3 is tightly correlated with camalexin synthesis and is regulated by PAD4 and PAD1. On the basis of these findings, we conclude that PAD3 almost certainly encodes an enzyme required for camalexin biosynthesis. Moreover, these results strongly support the idea that camalexin does not play a major role in plant resistance to P. syringae infection, although it is involved in resistance to a fungal pathogen.
We have assessed ultraviolet-B (UV-B)-induced injury in wild-type Arabidopsis thaliana and two mutants with altered aromatic secondary product biosynthesis. Arabidopsis mutants defective in the ability to synthesize UV-B-absorbing compounds (flavonoids in transparent testa 5 [tt5] and sinapate esters in ferulic acid hydroxylase 1 [fah1]) are more sensitive to UV-B than is the wild-type Landsberg erecta. Despite its ability to accumulate UV-absorptive flavonoid compounds, the ferulic acid hydroxylase mutant fah1 exhibits more physiological injury (growth inhibition and foliar lesions) than either wild type or tt5. The extreme UV-B sensitivity of fah1 demonstrates the importance of hydroxycinnamate esters as UV-B protectants. Consistent with the whole-plant response, the highest levels of lipid and protein oxidation products were seen in fah1. Ascorbate peroxidase enzyme activity was also increased in the leaves of UV-B-treated plants in a dose- and genotype-dependent manner. These results demonstrate that, in A. thaliana, hydroxycinnamates are more effective UV-B protectants than flavonoids. The data also indicate that A. thaliana responds to UV-B as an oxidative stress, and sunscreen compounds reduce the oxidative damage caused by UV-B.
High density oligonucleotide array technology is widely used in many areas of biomedical research for quantitative and highly
parallel measurements of gene expression. Affymetrix GeneChip arrays are the most popular. In this technology each gene is
typically represented by a set of 11–20 pairs of probes. In order to obtain expression measures it is necessary to summarize
the probe level data. Using two extensive spike‐in studies and a dilution study, we developed a set of tools for assessing
the effectiveness of expression measures. We found that the performance of the current version of the default expression measure
provided by Affymetrix Microarray Suite can be significantly improved by the use of probe level summaries derived from empirically
motivated statistical models. In particular, improvements in the ability to detect differentially expressed genes are demonstrated.
Within the Aphidoidea, most species of Aphididae, as long as they are in small numbers and not carrying
plant viruses, do little perceptible damage to their food plants. In species that cause toxicoses, it is usually
assumed that some component of the saliva must be responsible. Paradoxically, however, the salivary
enzymes of Aphididae are similar to those that already occur in plants – oxidases and enzymes that
depolymerize polysaccharides – and the salivary enzymes are injected in very small amounts relative to their
counterparts in the plant. Damage to plants triggers defensive, biochemical responses, and it is suggested that
the injected enzymes serve mainly to divert or counter responses at the immediate interface of stylets and
plant tissues. The saliva of Aphididae contains non-enzymic, reducing compounds which, in the presence of
oxidases, can combine with and inactivate defensive phytochemicals – including those released in response
to damage and transported in the phloem sieve tube sap on which Aphididae feed. Salivary and gut oxidases
deactivate ingested phytochemicals by oxidative polymerization. Aphididae inject saliva into sieve tubes
before sustained ingestion of sap, and this saliva has been presumed to condition the sieve tubes, but in what
way remains unclear. It is suggested that there is a dynamic biochemical interaction between aphids and
plants; that the interaction is usually well balanced for most of the Aphididae; hence, no outcome is readily
observable. Where a significant imbalance occurs, however, either the aphid is unable to feed, i.e. the plant
is resistant, and/or the aphid does not effectively counter a hypersensitive response. Not all plant responses
are disadvantageous to aphids. Gall-forming Aphidoidea trigger and control abnormal growth in the plant
to the insects' advantage, possibly by eliciting vigorous oxidation in selective meristematic tissues, thereby
limiting supply of molecular oxygen and inhibiting oxygen-dependent growth-controls. Current problems
and possible approaches for further research are reviewed.
To determine the relative importance of different potential host plants for supporting populations of the cabbage root fly, wild and cultivated crucifers were sampled for pupae at four locations during 1971-3. In addition, eighty-three species of Cruciferae native to or naturalized in the British Isles were inoculated with cabbage root fly eggs in a glasshouse to determine which species could support the larvae.
In the field, most pupae (28-7/plant) were collected from untreated cauliflowers. Fewer pupae (i-7–8-6/plant) were obtained from untreated crops of Brussels sprout, cabbage and swede. Applications of chlorfenvinphos reduced populations to two or less pupae per plant on all crops. Of five common weed species sampled, only Raphanus raphanistrum produced as many pupae as certain of the untreated brassica crops. Pupae did not occur in samples from Capsella bursa-pastoris but Sisymbrium officinale, Thlaspi arvense and Sinapis arvensis usually supported low numbers.
In the glasshouse, only forty-four of the eighty-three cruciferous species tested supported larval development. Most pupae were obtained from 12-wk-old plants of Barbarea intermedia. B. stricta, Brassica napus, Cochlearia officinalis and R. raphanistrum and from 24-wk-old plants of Brassica rapa, Erysimum aureum, Cochlearia anglica and C. officinalis. Plant age considerably affected pupal production. Plants within a genus often gave similar results, pupae not being recovered from any of the Diplotaxis or Arabis species tested, or from young plants of Erysimum spp. In other families, Reseda lutea and R. luteola supported larval development, but the widely-separated Plantago major did not.
Arguments for and against the removal of cruciferous weeds from the vicinity of cruciferous crops are discussed.
Designing PCR and sequencing primers are essential activities for molecular biologists around the world. This chapter assumes
acquaintance with the principles and practice of PCR, as outlined in, for example, refs.
1–4.
Abstract Emissions of volatiles increase following herbivory from many plant species and volatiles may serve multiple functions. Herbivore-induced volatiles attract predators and parasitoids of herbivores and are often assumed to benefit plants by facilitating top-down control of herbivores; this benefit of induced emissions has been tested only a few times. Volatile compounds released by experimentally clipped sagebrush shoots have been shown to reduce levels of chewing damage experienced by other shoots on the same plant and on neighboring sagebrush plants. In this study, I asked whether experimental clipping attracted predators of herbivorous insects to sagebrush shoots. I also evaluated aphid populations and chewing damage on clipped and unclipped shoots and whether predators were likely to have caused differences in aphids and chewing damage. Shoots that had been clipped recruited more generalist predators, particularly coccinellids and Geocoris spp. in visual surveys conducted during two seasons. Clipping also caused increased numbers of parasitized aphids in one season. Ants were common tending aphids but were not significantly affected by clipping. Despite the increase in generalist predators, clipped plants were more likely to support populations of aphids that increased during both seasons compared to aphids on unclipped control plants. Clipped shoots suffered less damage by chewing herbivores in the 1-year in which this was measured. Chewing damage was not correlated with numbers of predators. These results suggest that predators and parasitoids were attracted to experimentally clipped sagebrush plants but that these predators were not effective at reducing net damage to the plant. This conclusion is not surprising as much of the herbivory is inflicted by grasshoppers and deer, herbivores that are not vulnerable to the predators attracted to sagebrush volatiles. More generally, it should not be assumed that predators that are attracted by herbivore-induced volatiles necessarily benefit the plant without testing this hypothesis under field conditions.
Plants face a daunting array of creatures that eat them, bore into them, and otherwise use virtually every plant part for food, shelter, or both. But although plants cannot flee from their attackers, they are far from defenseless. In addition to adaptations like thorns, which may be produced in response to attack, plants actively alter their chemistry and physiology in response to damage. For instance, young potato plant leaves being eaten by potato beetles respond by producing chemicals that inhibit beetle digestive enzymes. Over the past fifteen years, research on these induced responses to herbivory has flourished, and here Richard Karban and Ian T. Baldwin present the first comprehensive evaluation and synthesis of this rapidly developing field. They provide state-of-the-discipline reviews and highlight areas where new research will be most productive. Their comprehensive overview will be welcomed by a wide variety of theoretical and applied researchers in ecology, evolutionary biology, plant biology, entomology, and agriculture.
Plants are equipped with an array of defense mechanisms to protect themselves against herbivorous insects and microbial pathogens. Some are pre-existing while others are only activated upon insect attack or pathogen invasion. However, induced defense responses entail fitness costs. Therefore, plants possess elaborate regulatory mechanisms that efficiently coordinate activation of attacker-specific defenses. A major focus in plant defense signaling research is to uncover key mechanisms by which plants tailor their responses to different attackers, and to investigate how plants cope with simultaneous interactions with multiple aggressors. The phytohormones salicylic acid (SA) and jasmonic acid (JA) play a major role in the regulation of induced defense mechanisms against biotrophic pathogens and insect herbivores, respectively. Cross-talk between SA and JA defense signaling pathways is thought to allow fine-tuning of the defense response to the attacker encountered. In Arabidopsis, pharmacological experiments revealed that SA exerts a strong antagonistic effect on JA-responsive genes, such as PLANT DEFENSIN1.2 (PDF1.2), indicating that the SA pathway can be prioritized over the JA pathway. This antagonistic effect of SA on JA signaling is a robust phenomenon: It is conserved among Arabidopsis accessions, and JA-responsive gene expression is readily suppressed by SA for several days, even when triggered by very low doses of SA. Time interval studies revealed that SA has a window of opportunity to suppress MeJA-responsive gene expression, and that this time interval correlates with the SA-induced redox change in the plant tissue. Thus, redox modulation is likely to play a central role in the regulatory mechanism underlying SA/JA cross-talk. Analysis of the Arabidopsis mutant npr1, impaired in SA signal transduction, revealed that the antagonistic effect of SA on JA signaling requires the regulatory protein NPR1. Nuclear localization of NPR1, which is essential for SA-mediated defense gene expression, is not required for suppression of JA-responsive genes, indicating that cross-talk between SA and JA is modulated through a function of NPR1 in the cytosol. TGA transcription factors are similarly required for both SA-dependent gene expression and SA-mediated suppression of JA signaling. However, TGA factors are unlikely to exert their effect through direct interaction with the promoter of JA-responsive genes such as PDF1.2, as removal of the TGA binding site in this promoter did not affect cross-talk. Promoter analysis of SA-suppressed, MeJA-inducible cross-talk genes revealed enrichment of the I box and the GCC box motif. Site-directed mutagenesis of the I box motif in the PDF1.2 promoter did not affect suppression of this gene by SA, indicating that the I box is not essential in mediating cross-talk. The role of the GCC box in cross-talk regulation should be further elucidated. This motif is required for MeJA-responsiveness in the PDF1.2 promoter, and thus provides an attractive target for SA-mediated suppression. Collectively, this work provides novel insight into how plants regulate their defense response upon attack by multiple aggressors, and may prove valuable for the development of novel strategies for crop protection.
The perception of pathogen or microbe-associated molecular pattern molecules by plants triggers a basal defense response analogous to animal innate immunity and is defined partly by the deposition of the glucan polymer callose at the cell wall at the site of pathogen contact. Transcriptional and metabolic profiling in Arabidopsis mutants, coupled with the monitoring of pathogen-triggered callose deposition, have identified major roles in pathogen response for the plant hormone ethylene and the secondary metabolite 4-methoxy-indol-3-ylmethylglucosinolate. Two genes, PEN2 and PEN3, are also necessary for resistance to pathogens and are required for both callose deposition and glucosinolate activation, suggesting that the pathogen-triggered callose response is required for resistance to microbial pathogens. Our study shows that well-studied plant metabolites, previously identified as important in avoiding damage by herbivores, are also required as a component of the plant defense response against microbial pathogens.
Salivary proteins (SPs) of Schizaphis graminum, Acyrthosiphon pisum and Myzus persicae were studied after probing and feeding on different artificial diets. Salivary sheaths as well as apical lumps of saliva were found, presumably representing subsequently excreted saliva of different types. Phenoloxidase, pectinase and peroxidase activities were detected by staining the enzyme-converted products, thus confirming these enzyme activities found earlier by others. Proteinase and cellulase were not found. SPs in three major SDS-PAGE bands, at 154 and 66/69 kDa, were collected in fluid diets (soluble fraction) and as sheath material (solid fraction) attached to the membranes covering these diets. Proteins of both fractions presumably represented the enzymatic activities found, although this could not be proven. The lack of electrophoretic mobility of the undenaturated (isoelectrofocusing and PAGE) active proteins meant that they could not be separated, whereas the mobile denaturated (SDS-PAGE) proteins had lost their enzyme activity. Polyclonal antibodies, anti-SP154 and anti-SP66/69, both cross-reacted to most salivary proteins in Western blots. They also reacted to sheath material and to the principal salivary glands. For further studies of saliva some monoclonal antibodies were developed. The complexity of salivation and the relation of the results obtained to the behaviourally known secretion periods is discussed.
The screening of many endpoints when comparing groups from different strains, searching for some statistically significant difference, raises the multiple comparisons problem in its most severe form. Using the 0.05 level to decide which of the many endpoints' differences are statistically significant, the probability of finding a difference to be significant even though it is not real increases far beyond 0.05. The traditional approach to this problem has been to control the probability of making even one such error--the Bonferroni procedure being the most familiar procedure achieving such control. However, the incurred loss of power stemming from such control led many practitioners to neglect multiplicity control altogether. The False Discovery Rate (FDR), suggested by Benjamini and Hochberg [J Royal Stat Soc Ser B 57 (1995) 289], is a new, different, and compromising point of view regarding the error in multiple comparisons. The FDR is the expected proportion of false discoveries among the discoveries, and controlling the FDR goes a long way towards controlling the increased error from multiplicity while losing less in the ability to discover real differences. In this paper we demonstrate the problem in two studies: the study of exploratory behavior [Behav Brain Res (2001)], and the study of the interaction of strain differences with laboratory environment [Science 284 (1999) 1670]. We explain the FDR criterion, and present two simple procedures that control the FDR. We demonstrate their increased power when used in the above two studies.
Phloem feeding involves unique biological interactions between the herbivore and its host plant. The economic importance of aphids, whiteflies, and other phloem-feeding insects as pests has prompted research to isolate sources of resistance to piercing-sucking insects in crops. However, little information exists about the molecular nature of plant sensitivity to phloem feeding. Recent discoveries involving elicitation by plant pathogens and chewing insects and limited studies on phloem feeders suggest that aphids are capable of inducing responses in plants broadly similar to those associated with pathogen infection and wounding. Our past work showed that compatible aphid feeding on leaves of Arabidopsis thaliana induces localized changes in levels of transcripts of genes that are also associated with infection, mechanical damage, chewing herbivory, or resource allocation shifts. We used microarray and macroarray gene expression analyses of infested plants to better define the response profile of A. thaliana to M. persicae feeding. The results suggest that genes involved in oxidative stress, calcium-dependent signaling, pathogenesis-related responses, and signaling are key components of this profile in plants infested for 72 or 96 h. The use of plant resistance to aphids in crops will benefit from a better understanding of induced responses. The establishment of links between insect elicitation, plant signaling associated with phloem feeding, and proximal resistance mechanisms is critical to further research progress in this area.
In Arabidopsis spp., the jasmonate (JA) response pathway generally is required for defenses against necrotrophic pathogens and chewing insects, while the salicylic acid (SA) response pathway is generally required for specific, resistance (R) gene-mediated defenses against both biotrophic and necrotrophic pathogens. For example, SA-dependent defenses are required for resistance to the biotrophic fungal pathogen Erysiphe cichoracearum UCSC1 and the bacterial pathogen Pseudomonas syringae pv. maculicola, and also are expressed during response to the green peach aphid Myzus persicae. However, recent evidence indicates that the expression of JA-dependent defenses also may confer resistance to E. cichoracearum. To confirm and to extend this observation, we have compared the disease and pest resistance of wild-type Arabidopsis plants with that of the mutants coil, which is insensitive to JA, and cev1, which has constitutive JA signaling. Measurements of the colonization of these plants by E. cichoracearum, P. syringae pv. maculicola, and M. persicae indicated that activation of the JA signal pathway enhanced resistance, and was associated with the activation of JA-dependent defense genes and the suppression of SA-dependent defense genes. We conclude that JA and SA induce alternative defense pathways that can confer resistance to the same pathogens and pests.
High density oligonucleotide array technology is widely used in many areas of biomedical research for quantitative and highly parallel measurements of gene expression. Affymetrix GeneChip arrays are the most popular. In this technology each gene is typically represented by a set of 11-20 pairs of probes. In order to obtain expression measures it is necessary to summarize the probe level data. Using two extensive spike-in studies and a dilution study, we developed a set of tools for assessing the effectiveness of expression measures. We found that the performance of the current version of the default expression measure provided by Affymetrix Microarray Suite can be significantly improved by the use of probe level summaries derived from empirically motivated statistical models. In particular, improvements in the ability to detect differentially expressed genes are demonstrated.
Glucosinolates are a group of defense-related secondary metabolites found in Arabidopsis and other cruciferous plants. Levels of leaf glucosinolates are regulated during plant development and increase in response to mechanical damage or insect feeding. The Arabidopsis TU8 mutant has a developmentally altered leaf glucosinolate profile: aliphatic glucosinolate levels drop off more rapidly, consistent with the early senescence of the mutant, and the levels of two indole glucosinolates are uniformly low. In TU8 seeds, four long-chain aliphatic glucosinolates have significantly increased levels, whereas the indolyl-3-methyl glucosinolate level is significantly reduced relative to wild type. Genetic mapping and DNA sequencing identified the TU8 mutation as tfl2-6, a new allele of TERMINAL FLOWER2 (TFL2), the only Arabidopsis homolog of animal HETEROCHROMATIN PROTEIN1 (HP1). TU8 (tfl2-6) has other previously identified tfl2 phenotypes, including an early transition to flowering, altered meristem structure, and stunted leaves. Analysis of two additional alleles, tfl2-1 and tfl2-2, showed glucosinolate profiles similar to those of line TU8 (tfl2-6).
In Arabidopsis and other Brassicaceae, the enzyme myrosinase (beta-thioglucoside glucohydrolase, TGG) degrades glucosinolates to produce toxins that deter herbivory. A broadly applicable selection for meiotic recombination between tightly linked T-DNA insertions was developed to generate Arabidopsis tgg1tgg2 double mutants and study myrosinase function. Glucosinolate breakdown in crushed leaves of tgg1 or tgg2 single mutants was comparable to that of wild-type, indicating redundant enzyme function. In contrast, leaf extracts of tgg1tgg2 double mutants had undetectable myrosinase activity in vitro, and damage-induced breakdown of endogenous glucosinolates was apparently absent for aliphatic and greatly slowed for indole glucosinolates. Maturing leaves of myrosinase mutants had significantly increased glucosinolate levels. However, developmental decreases in glucosinolate content during senescence and germination were unaffected, showing that these processes occur independently of TGG1 and TGG2. Insect herbivores with different host plant preferences and feeding styles varied in their responses to myrosinase mutations. Weight gain of two Lepidoptera, the generalist Trichoplusia ni and the facultative Solanaceae-specialist Manduca sexta, was significantly increased on tgg1tgg2 double mutants. Two crucifer-specialist Lepidoptera had differing responses. Whereas Plutella xylostella was unaffected by myrosinase mutations, Pieris rapae performed better on wild-type, perhaps due to reduced feeding stimulants in tgg1tgg2 mutants. Reproduction of two Homoptera, Myzus persicae and Brevicoryne brassicae, was unaffected by myrosinase mutations.
The problem of identifying differentially expressed genes in designed microarray experiments is considered. Lonnstedt and Speed (2002) derived an expression for the posterior odds of differential expression in a replicated two-color experiment using a simple hierarchical parametric model. The purpose of this paper is to develop the hierarchical model of Lonnstedt and Speed (2002) into a practical approach for general microarray experiments with arbitrary numbers of treatments and RNA samples. The model is reset in the context of general linear models with arbitrary coefficients and contrasts of interest. The approach applies equally well to both single channel and two color microarray experiments. Consistent, closed form estimators are derived for the hyperparameters in the model. The estimators proposed have robust behavior even for small numbers of arrays and allow for incomplete data arising from spot filtering or spot quality weights. The posterior odds statistic is reformulated in terms of a moderated t-statistic in which posterior residual standard deviations are used in place of ordinary standard deviations. The empirical Bayes approach is equivalent to shrinkage of the estimated sample variances towards a pooled estimate, resulting in far more stable inference when the number of arrays is small. The use of moderated t-statistics has the advantage over the posterior odds that the number of hyperparameters which need to estimated is reduced; in particular, knowledge of the non-null prior for the fold changes are not required. The moderated t-statistic is shown to follow a t-distribution with augmented degrees of freedom. The moderated t inferential approach extends to accommodate tests of composite null hypotheses through the use of moderated F-statistics. The performance of the methods is demonstrated in a simulation study. Results are presented for two publicly available data sets.
Glucosinolates are sulfur-rich, anionic natural products that upon hydrolysis by endogenous thioglucosidases called myrosinases produce several different products (e.g., isothiocyanates, thiocyanates, and nitriles). The hydrolysis products have many different biological activities, e.g., as defense compounds and attractants. For humans these compounds function as cancer-preventing agents, biopesticides, and flavor compounds. Since the completion of the Arabidopsis genome, glucosinolate research has made significant progress, resulting in near-complete elucidation of the core biosynthetic pathway, identification of the first regulators of the pathway, metabolic engineering of specific glucosinolate profiles to study function, as well as identification of evolutionary links to related pathways. Although much has been learned in recent years, much more awaits discovery before we fully understand how and why plants synthesize glucosinolates. This may enable us to more fully exploit the potential of these compounds in agriculture and medicine.