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Molecular Communications between Plants and Microbes
... Genome-wide association studies have been used in selecting desirable plant traits and in the manipulation of plants and their beneficial microbes [1]. Transcriptomic studies identify which gene/s are up/downregulated, what factors, especially inducers are involved and what developmental stage of the host/pathogen interaction [14,16,[22][23][24][25][26]. As such, when the underlying mechanisms of plant-microbe interactions are properly investigated, modulation, manipulation and inoculation strategies can be developed to meet crop growth, increased yield and pathogen control. ...
... At the outset, our group specializes in investigating resilient plants and/or their inherent microbial associations, aiming to translate and interpret their bioprospects into sustainable, eco-friendly, and cost-effective agricultural crop productivity [49][50][51][52][53][54][55]. In this study, we characterized two novel PGP bacterial endophytes from in vitro tissue culture attempts using Euphorbia prostrata (EP) and extensively investigated their ability to promote plant growth and productivity in agricultural crop models. ...
Euphorbiaceae is a highly diverse family of plants ranging from trees to ground-dwelling
minute plants. Many of these have multi-faceted attributes like ornamental, medicinal, industrial, and
food-relevant values. In addition, they have been regarded as keystone resources for investigating
plant-specific resilience mechanisms that grant them the dexterity to withstand harsh climates. In the
present study, we isolated two co-culturable bacterial endophytes, EP1-AS and EP1-BM, from the
stem internodal segments of the prostate spurge, Euphorbia prostrata, a plant member of the succulent
family Euphorbiaceae. We characterized them using morphological, biochemical, and molecular
techniques which revealed them as novel strains of Enterobacteriaceae, Lelliotia amnigena. Both the
isolates significantly were qualified during the assaying of their plant growth promotion potentials.
BM formed fast-growing swarms while AS showed growth as rounded colonies over nutrient agar.
We validated the PGP effects of AS and BM isolates through in vitro and ex vitro seed-priming
treatments with wheat and tomato, both of which resulted in significantly enhanced seed germination
and morphometric and physiological plant growth profiles. In extended field trials, both AS and BM
could remarkably also exhibit productive yields in wheat grain and tomato fruit harvests. This is
probably the first-ever study in the context of PGPB endophytes in Euphorbia prostrata. We discuss
our results in the context of promising agribiotechnology translations of the endophyte community
associated with the otherwise neglected ground-dwelling spurges of Euphorbiaceae.
Soil salinity is a major environmental stressor impacting global food production. Staple crops like wheat experience significant yield losses in saline environments. Bioprospecting for beneficial microbes associated with stress-resistant plants offers a promising strategy for sustainable agriculture. We isolated two novel endophytic bacteria, Bacillus cereus (ADJ1) and Priestia aryabhattai (ADJ6), from Agave desmettiana Jacobi. Both strains displayed potent plant growth-promoting (PGP) traits, such as producing high amounts of indole-3-acetic acid (9.46, 10.00 µgml⁻¹), ammonia (64.67, 108.97 µmol ml⁻¹), zinc solubilization (Index of 3.33, 4.22, respectively), ACC deaminase production and biofilm formation. ADJ6 additionally showed inorganic phosphate solubilization (PSI of 2.77), atmospheric nitrogen fixation, and hydrogen cyanide production. Wheat seeds primed with these endophytes exhibited enhanced germination, improved growth profiles, and significantly increased yields in field trials. Notably, both ADJ1 and ADJ6 tolerated high salinity (up to 1.03 M) and significantly improved wheat germination and seedling growth under saline stress, acting both independently and synergistically. This study reveals promising stress-tolerance traits within endophytic bacteria from A. desmettiana. Exploiting such under-explored plant microbiomes offers a sustainable approach to developing salt-tolerant crops, mitigating the impact of climate change-induced salinization on global food security.
Global warming not only alters phenology but also nutritional quality and defense compounds in plants, which consequently hinders their defense against herbivorous insects. In this study, the performance of Spodoptera litura was analyzed to observe the effects of high temperatures on chemical-based defense in plants in the context of insect–plant interaction. Results show that high temperature reduced the nutritional value and content of defense compounds in the foliage of yellow cress (Rorippa dubia). These alterations negatively affected the performance of second instar S. litura larvae feeding on plants grown at high temperature. Low quality of the food source is likely the key cause of slow development of larvae. Adaptation of herbivorous insects known as compensatory feeding is projected resulting in more crop losses under global warming. Our data reveal temperature-induced reduction in the content of defensive compounds (in constitutive resistance) along with lower response capability against herbivore attacks (in induced resistance), which indicate a decrease in plant fitness. High temperatures caused by global warming negatively affect crop production and are expected to increase the burden on plant protection practices.
Rising global temperatures are associated with increases in the geographic range, population size, and feeding voracity of insect herbivores. Although it is well established that the plant hormone jasmonate (JA) promotes durable resistance to many ectothermic herbivores, little is known about how JA-mediated defense is influenced by rising temperatures. Here, we used the Arabidopsis-Trichoplusia ni (cabbage looper) interaction to investigate the relative contribution of JA and elevated temperature to host resistance. Video monitoring of T. ni larval behavior showed that elevated temperature greatly enhanced defoliation by increasing the bite rate and total time spent feeding, whereas loss of resistance in a JA-deficient mutant did not strongly affect these behaviors. The acceleration of insect feeding at elevated temperature was not attributed to decreases in wound-induced JA biosynthesis, expression of JA-responsive genes, or the accumulation of defensive glucosinolates prior to insect challenge. Quantitative proteomic analysis of insect frass, however, provided evidence for a temperature-dependent increase in the production of T. ni digestive enzymes. Our results demonstrate that temperature-driven stimulation of T. ni feeding outweighs the protective effects of JA-mediated resistance in Arabidopsis, thus highlighting a potential threat to plant resilience in a warming world.
Herbivory can induce both general and specific responses in plants that modify direct and indirect defence against subsequent herbivory. The type of induction (local versus systemic induction, single versus multiple defence induction) likely depends both on herbivore identity and relationships among different responses. We examined the effects of two above-ground chewing herbivores (caterpillar, weevil) and one sucking herbivore (aphid) on indirect defence responses in leaves and direct defence responses in both leaves and roots of tallow tree, Triadica sebifera. We also included foliar applications of methyl jasmonate (MeJA) and salicylic acid (SA). We found that chewing herbivores and MeJA increased above-ground defence chemicals but SA only increased below-ground total flavonoids. Herbivory or MeJA increased above-ground indirect defence response (extrafloral nectar) but SA decreased it. Principal component analysis showed there was a trade-off between increasing total root phenolics and tannins (MeJA, chewing) versus latex and total root flavonoids (aphid, SA). For individual flavonoids, there was evidence for systemic induction (quercetin), trade-offs between compounds (quercetin versus kaempferitrin) and trade-offs between above-ground versus below-ground production (isoquercetin). Our results suggest that direct and indirect defence responses in leaves and roots depend on herbivore host range and specificity along with feeding mode. We detected relationships among some defence response types, while others were independent. Including multiple types of insects to examine defence inductions in leaves and roots may better elucidate the complexity and specificity of defence responses of plants.
Mortierella and Ilyonectria include common species of soil fungi which are frequently detected as root endophytes in many plants including Populus spp. However, the ecological roles of these and other endophytic fungi with respect to plant growth and function are still not well understood. The functional ecology of two key taxa from the Populus rhizobiome, Mortierella elongata PMI93 and Ilyonectria europaea PMI82, was studied by coupling forest soil bioassays with environmental metatranscriptomics. Using soil bioassay experiments amended with fungal inoculants, M. elongata was observed to promote the growth of Populus. This response was cultivar independent. In contrast, I. europaea had no visible effect on Populus growth. Metatranscriptomic studies reveal that these fungi impact rhizophytic and endophytic activities in Populus and induce shifts in soil and root microbial communities. Differential expression of core genes in P. trichocarpa roots was observed in response to both fungal species. Expression of Populus genes for lipid signaling and nutrient uptake were up-regulated and expression of genes associated with gibberellin signaling were altered in plants inoculated with M elongata, but not I. europaea. Up-regulation of genes for growth promotion, down-regulation of genes for several LRR-receptors/kinases, and alteration of expression of genes associated with plant defense responses (e.g., JA/ET/SA pathways) also suggest that M. elongata manipulates plant defenses while promoting plant growth.
Climate change is predicted to alter relationships between trophic levels by changing the phenology of interacting species. We tested whether synchrony between two critical phenological events, budburst of host species and larval emergence from diapause of eastern spruce budworm, increased at warmer temperatures in the boreal forest in northeastern Canada. Budburst was up to 4.6 ± 0.7 days earlier in balsam fir and up to 2.8 ± 0.8 days earlier in black spruce per degree increase in temperature, in naturally occurring microclimates. Larval emergence from diapause did not exhibit a similar response. Instead, larvae emerged once average ambient temperatures reached 10°C, regardless of differences in microclimate. Phenological synchrony increased with warmer microclimates, tightening the relationship between spruce budworm and its host species. Synchrony increased by up to 4.5 ± 0.7 days for balsam fir and up to 2.8 ± 0.8 days for black spruce per degree increase in temperature. Under a warmer climate, defoliation could potentially begin earlier in the season, in which case, damage on the primary host, balsam fir may increase. Black spruce, which escapes severe herbivory because of a 2‐week delay in budburst, would become more suitable as a resource for the spruce budworm. The northern boreal forest could become more vulnerable to outbreaks in the future.
The midgut of insects is involved in digestion, osmoregulation and immunity. Although several defensive strategies are present in this organ, its organization and function may be disturbed by some insecticidal agents, including bioactive proteins like lectins and protease inhibitors (PIs) from plants. PIs interfere with digestion, leading to poor nutrient absorption and decreasing amino acid bioavailability. Intake of PIs can delay development, cause deformities and reduce fertility. Ingestion of PIs may lead to changes in the set of proteases secreted in the insect gut, but this response is often insufficient and results in aggravation of the malnutrition status. Lectins are proteins that are able to interact with glycoconjugates, including those linked to cell surfaces. Their effects on the midgut include disruption of the peritrophic matrix, brush border and secretory cell layer; induction of apoptosis and oxidative stress; interference with nutrient absorption and transport proteins; and damaging effects on symbionts. In addition, lectins can cross the intestinal barrier and reach the hemolymph. The establishment of resistant insect populations due to selective pressure resulting from massive use of a bioactive protein is an actual possibility, but this can be minimized by the multiple mode‐of‐action of these proteins, mainly the lectins. © 2018 Society of Chemical Industry
Biological control utilizes natural living organism, such as insects, herbivorous fish, other animals, disease organisms and competitive plants to limit their growth. In biological control method, it is not possible to eradicate weeds but weed population can be reduced. This method is not useful to control all types of weeds. Introduced weeds are best targets for biological control. Biological control is least harmful to the environment, have no residual effect, relatively cheaper, having comparatively long lasting effect, harmless to non-targeted plants, very effective in control of weeds in non cropped areas. Besides this some of the fish, snails and other animals convert weed vegetation into seafood. This review enumerates various biological control mechanisms used for weed control. The classical examples of biological weed control have also been enlisted.
Herbivorous insects are responsible for large losses to agriculture through feeding damage itself but also by vectoring pathogens such as viruses. Plants have evolved various mechanisms to defend themselves against insects, including the production of specialised metabolites that act as natural insecticides. Throughout history, plants and plant extracts harbouring specialised metabolites have been exploited by man for their anti-insect properties. Also, commercial insecticides are often based on plant-specialised metabolites and adapted further e.g. to give them the physicochemical properties that render them systemic. The development and application of these synthetic pesticides has made it possible to scale up the production and to increase the yield of food crops worldwide. However, their adversary effects on the environment and on non-target organisms, first discussed in Rachel Carson’s Silent Spring, continue to cause debate and recently resulted in a ban on the use of certain pesticides in the European Union. The trait of insect defence has been largely overlooked during crop domestication and resulted in basically unarmed crop plants. Endogenous production of specialised metabolites could be re-introduced in modern crop varieties to retrieve self-defences. However, despite the fact that a plethora of specialised metabolites from plants has been described, studies that validate their deterrent or insecticidal effect in planta (crop), let alone in field situations, are sparse. To answer the question whether it is feasible to re-introduce endogenous insecticides to bring about insect resistance, the defence metabolites of plants, their synthesis and regulatory mechanisms underlying their production are examined.
As an ancient seed plant, cycads are one of the few gymnosperms that develop a root symbiosis with cyanobacteria, which has allowed cycads to cope with harsh geologic and climatic conditions during the evolutionary process. However, the endophytic microbes in cycad roots remain poorly identified. In this study, using next-generation sequencing techniques, we investigated the microbial diversity and composition of both the coralloid and regular roots of Cycas bifida (Dyer) K.D. Hill. Highly diverse endophytic communities were observed in both the coralloid and regular roots. Of the associated bacteria, the top five families were the Nostocaceae, Sinobacteraceae, Bradyrhizobiaceae, Bacillaceae, and Hyphomicrobiaceae. The Nectriaceae, Trichocomaceae, and Incertae sedis were the predominant fungal families in all root samples. A significant difference in the endophytic bacterial community was detected between coralloid roots and regular roots, but no difference was observed between the fungal communities in the two root types. Cyanobacteria were more dominant in coralloid roots than in regular roots. The divergence of cycad root structures and the modified physiological processes may have contributed to the abundance of cyanobionts in coralloid roots. Consequently, the colonization of cyanobacteria inhibits the assemblage of other endophytes. Our results contribute to an understanding of the species diversity and composition of the cycad-endophyte microbiome and provide an abbreviated list of potential ecological roles of the core microbes present.
Flavonoids are structurally diverse secondary metabolites in plants, with a multitude of functions. These span from functions in regulating plant development, pigmentation, and UV protection, to an array of roles in defence and signalling between plants and microorganisms. Because of their prevalence in the human diet, many flavonoids constitute important components of medicinal plants and are used in the control of inflammation and cancer prevention. Advances in the elucidation of flavonoid biosynthesis and its regulation have led to an increasing number of studies aimed at engineering the flavonoid pathway for enhancing nutritional value and plant defences against pathogens and herbivores, as well as modifying the feeding value of pastures. Many future opportunities await for the exploitation of this colourful pathway in crops, pastures, and medicinal plants.
Significance
Despite the importance of liverworts as the earliest diverging land plant lineage to support fungal symbiosis, it is unknown whether filamentous pathogens can establish intracellular interactions within living cells of these nonvascular plants. Here, we demonstrate that an oomycete pathogen invades Marchantia polymorpha and related liverworts to form intracellular infection structures inside cells of the photosynthetic layer. Plants lacking this tissue layer display enhanced resistance to infection, revealing an architectural susceptibility factor in complex thalloid liverworts. Moreover, we show that dedicated host cellular trafficking proteins are recruited to pathogen interfaces within liverwort cells, supporting the idea that intracellular responses to microbial invasion originated in nonvascular plants.
Plant-insect interactions constitute a complex of system, whereby plants synthesize toxic compounds as the main defense strategy to combat herbivore assault, and insects deploy detoxification systems to cope with toxic plant compounds. Cytochrom P450s are among the main detoxification enzymes employed by insects to combat the chemical defenses of host plants. In this study, we used Nilaparvata lugens (BPH) to constitute an ideal system for studying plant-insect interactions. By feeding BPHs with artificial diets containing ethanol extracts, we show that biotype Y BPHs have a greater ability to metabolize exogenous substrates than biotype 1 BPHs. NlCPR knockdown inhibited the ability of BPHs to feed on YHY15. qRT-PCR was used to screen genes in the P450 family, and upregulation of CYP4C61, CYP6AX1, and CYP6AY1 induced by YHY15 was investigated. When the three P450 genes were knocked down, only CYP4C61 dsRNA treatment was inhibited the ability of BPHs to feed on YHY15. These results indicate that BPH P450 enzymes are a key factor in the physiological functions of BPH when feeding on BPH-resistant rice.
Many heritable mutualisms, in which beneficial symbionts are transmitted vertically between host generations, originate as antagonisms with parasite dispersal constrained by the host. Only after the parasite gains control over its transmission is the symbiosis expected to transition from antagonism to mutualism. Here, we explore this prediction in the mutualism between the fungus Rhizopus microsporus (Rm, Mucoromycotina) and a beta-proteobacterium Burkholderia, which controls host asexual reproduction. We show that reproductive addiction of Rm to endobacteria extends to mating, and is mediated by the symbiont gaining transcriptional control of the fungal ras2 gene, which encodes a GTPase central to fungal reproductive development. We also discover candidate G-protein-coupled receptors for the perception of trisporic acids, mating pheromones unique to Mucoromycotina. Our results demonstrate that regulating host asexual proliferation and modifying its sexual reproduction are sufficient for the symbiont’s control of its own transmission, needed for antagonism-to-mutualism transition in heritable symbioses. These properties establish the Rm-Burkholderia symbiosis as a powerful system for identifying reproductive genes in Mucoromycotina.
The purpose of this study was to evaluate the antifeedant and oviposition-deterring activity of total ginsenosides against P. rapae. Total ginsenosides exhibited increased antifeedant effects againstP. rapae. The highest nonselective and selective antifeedant activity were observed at 2.0% concentration where ginsenosides caused antifeedant percentages of 86.09 and 88.90, respectively. The total ginsenosides showed significantly oviposition-deterring activity of 77.78% against oviposition of P. rapae at 1.0% concentration. Total ginsenosides had antifeeding activity against P. rapae and inhibitory effects on its oviposition. Ginsenosides could be used as an agent to prepare botanical new pesticidal formulations.
Flavonoids, a class of polyphenol secondary metabolites, are presented broadly in plants and diets. They are believed to have various bioactive effects including anti-viral, anti-inflammatory, cardioprotective, anti-diabetic, anti-cancer, anti-aging, etc. Their basic structures consist of C6 C3 C6 rings with different substitution patterns to produce a series of subclass compounds, and correlations between chemical structures and bioactivities have been studied before. Given their poor bioavailability, however, information about associations between structure and biological fate is limited and urgently needed. This review therefore attempts to bring some order into relationships between structure, activity as well as pharmacokinetics of bioactive flavonoids.
Background
Interactions between pathogenic oomycetes and microbiota residing on the surface of the host plant root are unknown, despite being critical to inoculum constitution. The nature of these interactions was explored for the polyphagous and telluric species Phytophthora parasitica. ResultsComposition of the rhizospheric microbiota of Solanum lycopersicum was characterized using deep re-sequencing of 16S rRNA gene to analyze tomato roots either free of or partly covered with P. parasitica biofilm. Colonization of the host root surface by the oomycete was associated with a shift in microbial community involving a Bacteroidetes/Proteobacteria transition and Flavobacteriaceae as the most abundant family. Identification of members of the P. parasitica-associated microbiota interfering with biology and oomycete infection was carried out by screening for bacteria able to (i) grow on a P. parasitica extract-based medium (ii), exhibit in vitro probiotic or antibiotic activity towards the oomycete (iii), have an impact on the oomycete infection cycle in a tripartite interaction S. lycopersicum-P. parasitica-bacteria. One Pseudomonas phylotype was found to exacerbate disease symptoms in tomato plants. The lack of significant gene expression response of P. parasitica effectors to Pseudomonas suggested that the increase in plant susceptibility was not associated with an increase in virulence. Our results reveal that Pseudomonas spp. establishes commensal interactions with the oomycete. Bacteria preferentially colonize the surface of the biofilm rather than the roots, so that they can infect plant cells without any apparent infection of P. parasitica. Conclusions
The presence of the pathogenic oomycete P. parasitica in the tomato rhizosphere leads to a shift in the rhizospheric microbiota composition. It contributes to the habitat extension of Pseudomonas species mediated through a physical association between the oomycete and the bacteria.
Bryophytes, including mosses, liverworts and hornworts are early land plants that have evolved key adaptation mechanisms to cope with abiotic stresses and microorganisms. Microbial symbioses facilitated plant colonization of land by enhancing nutrient uptake leading to improved plant growth and fitness. In addition, early land plants acquired novel defense mechanisms to protect plant tissues from pre-existing microbial pathogens. Due to its evolutionary stage linking unicellular green algae to vascular plants, the non-vascular moss Physcomitrella patens is an interesting organism to explore the adaptation mechanisms developed in the evolution of plant defenses to microbes. Cellular and biochemical approaches, gene expression profiles, and functional analysis of genes by targeted gene disruption have revealed that several defense mechanisms against microbial pathogens are conserved between mosses and flowering plants. P. patens perceives pathogen associated molecular patterns by plasma membrane receptor(s) and transduces the signal through a MAP kinase (MAPK) cascade leading to the activation of cell wall associated defenses and expression of genes that encode proteins with different roles in plant resistance. After pathogen assault, P. patens also activates the production of ROS, induces a HR-like reaction and increases levels of some hormones. Furthermore, alternative metabolic pathways are present in P. patens leading to the production of a distinct metabolic scenario than flowering plants that could contribute to defense. P. patens has acquired genes by horizontal transfer from prokaryotes and fungi, and some of them could represent adaptive benefits for resistance to biotic stress. In this review, the current knowledge related to the evolution of plant defense responses against pathogens will be discussed, focusing on the latest advances made in the model plant P. patens.
Plants respond to herbivore attack by launching two types of defenses: direct defense and indirect defense. Direct defense includes all plant traits that increase the resistance of host plants to insect herbivores by affecting the physiology and/or behavior of the attackers. Indirect defense includes all traits that by themselves do not have significant direct impact on the attacking herbivores, but can attract natural enemies of the herbivores and thus reduce plant loss. When plants recognize herbivore-associated elicitors, they produce and release a blend of volatiles that can attract predators, parasites, and other natural enemies. Known herbivore-associated elicitors include fatty acid-amino acid conjugates, sulfur-containing fatty acids, fragments of cell walls, peptides, esters, and enzymes. Identified plant volatiles include terpenes, nitrogenous compounds, and indoles. In addition, constitive traits including extrafloral nectars, food bodies, and domatia can be further induced to higher levels and attract natural enemies as well as provide food and shelter to carnivores. A better understanding of indirect plant defense at global and componential levels via advanced high throughput technologies may lead to utilization of indirect defense in suppression of herbivore damage to plants. This article is protected by copyright. All rights reserved.
Background
Previous studies on the bacteria associated with the bryophytes showed that there were abundant bacteria inhabited in/on these hosts. However, the type of bacteria and whether these discriminate between different bryophytes based on a particular factor remains largely unknown. ResultsThis study was designed to analyze the biodiversity and community of the bacteria associated with ten liverworts and ten mosses using Illumina-sequencing techniques based on bacterial 16S rRNA gene. A total of 125,762 high quality sequences and 437 OTUs were obtained from twenty bryophytes. Generally, there were no obvious differences between the richness of bacteria associated with liverworts and mosses; however, the diversity was significantly higher in liverworts than in mosses. The taxonomic analyses showed that there were abundant bacteria inhabited with each bryophyte and those primarily detected in all samples were within the phyla Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes, Armatimonadetes and Planctomycetes. In addition, bacteria assigned to Chloroflexi, Fibrobacteres, Gemmatimonadetes, Chlamydiae, group of TM6 and WCHB1-60 also appeared in part of the bryophytes. The assigned bacteria included those adapted to aquatic, anaerobic and even extreme drought environments, which is consistent with the bryophyte transition from aquatic to terrestrial conditions. Of them, approximately 10 recognized genera were shared by all the samples in a higher proportion, such as Burkholderia, Novosphingobium, Mucilaginibacter, Sorangium, Frankia, Frondihatitans, Haliangium, Rhizobacter, Granulicella and Hafnia, and 11 unclassified genera were also detected in all samples, which exhibited that large amounts of unclassified bacteria could interact with the bryophytes. The Heatmap and Principle Coordinate Analyses showed that bacteria associated with six mosses displayed a higher community similarity. Notably, the bacteria associated with another four mosses exhibited higher similarity with the ten liverworts. Conclusions
The result of further analysis of the bacterial community in different bryophytes revealed that the phylogeny of hosts might portray a strong influence on the associated bacterial community and that niche also played important roles when the hosts were phylogenetically more similar. Further studies are needed to confirm the role of phylogeny on bacterial communities and determine the level of influence on predicting which bacteria is associated with the host.
The microorganism–microorganism or microorganism–host interactions are the key strategy to colonize and establish in a variety of different environments. These interactions involve all ecological aspects, including physiochemical changes, metabolite exchange, metabolite conversion, signaling, chemotaxis and genetic exchange resulting in genotype selection. In addition, the establishment in the environment depends on the species diversity, since high functional redundancy in the microbial community increases the competitive ability of the community, decreasing the possibility of an invader to establish in this environment. Therefore, these associations are the result of a co-evolution process that leads to the adaptation and specialization, allowing the occupation of different niches, by reducing biotic and abiotic stress or exchanging growth factors and signaling. Microbial interactions occur by the transference of molecular and genetic information, and many mechanisms can be involved in this exchange, such as secondary metabolites, siderophores, quorum sensing system, biofilm formation, and cellular transduction signaling, among others. The ultimate unit of interaction is the gene expression of each organism in response to an environmental (biotic or abiotic) stimulus, which is responsible for the production of molecules involved in these interactions. Therefore, in the present review, we focused on some molecular mechanisms involved in the microbial interaction, not only in microbial–host interaction, which has been exploited by other reviews, but also in the molecular strategy used by different microorganisms in the environment that can modulate the establishment and structuration of the microbial community.
Although the increasing concentration of atmospheric carbon dioxide (CO2) accelerates the accumulation of carbohydrates and increases the biomass and yield of C3 crop plants, it also reduces their nitrogen concentration. The consequent changes in primary and secondary metabolites affect the palatability of host plants and the feeding of herbivorous insects. Aphids are phloem feeders and are considered the only feeding guild that positively responds to elevated CO2. In this review, we consider how elevated CO2 modifies host defenses, nutrients, and water-use efficiency by altering concentrations of the phytohormones jasmonic acid, salicylic acid, ethylene, and abscisic acid. We will describe how these elevated CO2-induced changes in defenses, nutrients, and water statusfacilitate specific stages of aphid feeding, including penetration, phloem-feeding, and xylem absorption. We conclude that a better understanding of the effects of elevated CO2 on aphids and on aphid damage to crop plants will require research on the molecular aspects of the interaction between plant and aphid but also research on aphid interactions with their intra- and inter-specific competitors and with their natural enemies.
Live-cell imaging of plant-pathogen interactions is often hampered by the tissue complexity and multicell layered nature of the host. Here, we established a novel pathosystem with the moss Physcomitrella patens as host for Phytophthora. The tip-growing protonema cells of this moss are ideal for visualizing interactions with the pathogen over time using high-resolution microscopy. We tested four Phytophthora species for their ability to infect P. patens and showed that P. sojae and P. palmivora were only rarely capable to infect P. patens. In contrast, P. infestans and P. capsici frequently and successfully penetrated moss protonemal cells, showed intracellular hyphal growth and formed sporangia. Next to these successful invasions, many penetration attempts failed. Here the pathogen was blocked by a barrier of cell wall material deposited in papilla-like structures, a defence response that is common in higher plants. Another common response is the upregulation of defence-related genes upon infection and also in moss we observed this upregulation in tissues infected with Phytophthora. For more advanced analyses of the novel pathosystem we developed a special set-up that allowed live-cell imaging of subcellular defence processes by high-resolution microscopy. With this set-up, we revealed that Phytophthora infection of moss induces repositioning of the nucleus, accumulation of cytoplasm and rearrangement of the actin cytoskeleton, but not of microtubules.
An analysis of the current state of knowledge of symbiotic fungal associations in 'lower' plants is provided Three fungal phyla, the Zygomycota, Ascomycota and Basidiomycota, are involved in forming these associations, each producing a distinctive suite of structural features in well-defined groups of 'lower' plants. Among the 'lower' plants only mosses and Equisetum appear to lack one or other of these types of association. The salient features of the symbioses produced by each fungal group are described and the relationships between these associations and those formed by the same or related fungi in 'higher' plants are discussed. Particular consideration is given to the question of the extent to which root-fungus associations in 'lower' plants are analogous to 'mycorrhizas' of 'higher' plants and the need for analysis of the functional attributes of these symbioses is stressed. Zygomycetous fungi colonize a wide range of extant lower land plants (hornworts, many hepatics, lycopods, Ophioglossales, Psilotales and Gleicheniaceae), where they often produce structures analogous to those seen in the vesicular-arbuscular (VA) mycorrhizas of higher plants, which are formed by members of the order Glomales. A preponderance of associations of this kind is in accordance with palaeobotanical and molecular evidence indicating that glomalean fungi produced the archetypal symbioses with the first plants to emerge on to land. It is shown, probably for the first time, that glomalean fungi forming typical VA mycorrhiza with a higher plant (Plantago lanceolata) can colonize a thalloid liverwort (Pellia epiphylla), producing arbuscules and vesicles in the hepatic. The extent to which these associations, which are structurally analogous to mycorrhizas, have similar functions remains to be evaluated. Ascomycetous associations are found in a relatively small number of families of leafy liverworts. The structural features of the fungal colonization of rhizoids and underground axes of these plants are similar to those seen in mycorrhizal associations of ericaceous plants like Vaccinium. Cross inoculation experiments have confirmed that a typical mycorrhizal endophyte of ericaceous plants, Hymenoscyphus ericae, will form associations in liverworts which are structurally identical to those seen in nature. Again, the functional significance of these associations remains to be examined. Some members of the Jungermanniales and Metzgeriales form associations with basidiomycetous fungi. These produce intracellular coils of hyphae, which are similar to the pelotons seen in orchid mycorrhizas, which also involve basidiomycetes. The fungal associates of the autotrophic Aneura and of its heterotrophic relative Cryptothallus mirabilis have been isolated. In the latter case it has been shown that the fungal symbiont is an ectomycorrhizal associate of Betula, suggesting that the apparently obligate nature of the association between the hepatic and Betula in nature is based upon requirement for this particular heterotroph.
Allelopathy plays a key role in both natural and managed ecosystems, especially agroecosystems such as weed control, crop protection, and crop re-establishment. Allelopathic chemical(s) are moved from the plant, mainly the leaves, to the soil by transfer mechanisms and their subsequent dissipation occurs in the soil. The allelopathic activity is confirmed through (a) bioassays with aqueous or various solvent extracts and residues, (b) fractionation, identification, and quantification of causative allelochemicals, and (c) mechanism studies on the allelochemicals. Most assessments of allelopathy involve bioassays of plant or soil extracts, leachates, fractions, and residues based on seed germination and seedling growth in laboratory and greenhouse experiments. Plant growth may be stimulated below the allelopathic threshold, but severe growth reductions may be observed above the threshold concentration depending upon the sensitivity of the receiving species. Petri dish bioassays with methanol extracts or fractions and causative phenolic allelochemicals showed significant phytotoxic activities in concentration-dependent manner. Delayed seed germination and slow root growth due to the extracts could be confounded with osmotic effects on rate of imbibition, delayed initiation of germination, and especially cell elongation; the main factor that affects root growth before and after the tip penetrates the seed coat. Microscopic approaches for extract evaluation at the ultrastructural level have been precisely investigated. Many wild plants have allelopathic potentials, and the activities and types and amount of causative compounds differ depending on the plant species. The incorporation of allelopathic substances into agricultural management may reduce the use of pesticides and lessen environmental deterioration.
Numerous insect herbivores can take up and store plant toxins as self-defense against their own natural enemies. Plant toxin sequestration is tightly linked with tolerance strategies that keep the toxins functional. Specific transporters have been identified that likely allow the herbivore to control the spatiotemporal dynamics of toxin accumulation. Certain herbivores furthermore possess specific enzymes to boost the bioactivity of the sequestered toxins. Ecologists have studied plant toxin sequestration for decades. The recently uncovered molecular mechanisms in combination with transient, non-transgenic systems to manipulate insect gene expression will help to understand the importance of toxin sequestration for food-web dynamics in nature.
Many plants have evolved adaptations in order to survive in low nitrogen environments. One of the best-known adaptations is that of plant symbiosis with nitrogen-fixing bacteria; this is the major route by which nitrogen is incorporated into plant biomass. A portion of this plant-associated nitrogen is then lost to insects through herbivory, and insects represent a nitrogen reservoir that is generally overlooked in nitrogen cycles. In this review we show three specialized plant adaptations that allow for the recovery of insect nitrogen; that is, plants gaining nitrogen from insects. First, we show specialized adaptations by carnivorous plants in low nitrogen habitats. Insect carnivorous plants such as pitcher plants and sundews (Nepenthaceae/Sarraceniaceae and Drosera respectively) are able to obtain substantial amounts of nitrogen from the insects that they capture. Secondly, numerous plants form associations with mycorrhizal fungi that can provide soluble nitrogen from the soil, some of which may be insect-derived nitrogen, obtained from decaying insects or insect frass. Finally, a specialized group of endophytic, insect-pathogenic fungi (EIPF) provide host plants with insect-derived nitrogen. These soil-inhabiting fungi form a remarkable symbiosis with certain plant species. They can infect a wide range of insect hosts and also form endophytic associations in which they transfer insect-derived nitrogen to the plant. Root colonizing fungi are found in disparate fungal phylogenetic lineages, indicating possible convergent evolutionary strategies between taxa, evolution potentially driven by access to carbon-containing root exudates.
Climate change will have a major bearing on survival and development of insects as a result of increase in CO2 and temperature. Therefore, we studied the direct effects of CO2 and temperature on larval development and metabolism in cotton bollworm, Helicoverpa armigera (Hübner). The larvae were reared under a range of CO2 (350, 550, and 750 ppm) and temperature (15, 25, 35, and 45°C) regimes on artificial diet. Elevated CO2 negatively affected the larval survival, larval weight, larval period, pupation, and adult emergence, but showed a positive effect on pupal weight, pupal period, and fecundity. Increase in temperature exhibited a negative effect on larval survival, larval period, pupal weights, and pupal period, but a positive effect on larval growth. Pupation and adult emergence were optimum at 25°C. Elevated CO2 and temperature increased food consumption and metabolism of larvae by enhancing the activity of midgut proteases, carbohydrases (amylase and cellulase), and mitochondrial enzymes and therefore may cause more damage to crop production. Elevated CO2 and global warming will affect insect growth and development, which will change the interactions between the insect pests and their crop hosts. Therefore, there is need to gain an understanding of these interactions to develop strategies for mitigating the effects of climate change.
Pteridophytes do not form dominant vegetation anywhere on the earth surface now, but have been replaced by the seed-bearing plants. Their occurrence in several small patches relays the message of richness. During the present study, 24 species of Pteridophytes were inventoried from Vilavancode, Kalkulam and Thovalai sacred groves of Kanyakumari district, Southern Western Ghats, India. Some of them are well known for their economic values. The species richness was more or less similar in the first two sacred groves, however, it was reduced to 6 in Thovalai. The terrestrial Pteridophytes were dominant over epiphytes. The lithophytic species were least in number. As a result of rapid urbanization and biotic interference these important plants are under threat and their population is being reduced, due to the ever-increasing human population. Some rare, endangered and endemic species are still present only in some pockets of this district and are conserved by indigenous people in the form of sacred groves.
Vallisneria natans is often used for the ecological restoration of aquatic vegetation. V. natans thalli were cultured under ambient (400 ppm) and increased carbon supply, with low (18 °C) and high temperature (25 °C). The thalli were used to examine the effects of increased carbon and high temperature on the growth, nitrogen metabolism and photosynthetic characteristics of this plant. At 18 °C, the relative growth rate (RGR), N uptake rate and nitrate reductase (NR) activity of V. natans thalli grown under ambient carbon supply were lower than those under increased carbon supply. The increased carbon supply decreased the RGR, N uptake rate, NR activity and maximum inorganic carbon (Ci) -saturated photosynthetic rate (Vmax) of V. natans when it was cultured at 25 °C. Regardless of the carbon supply levels, the growth, nitrogen uptake capacity and photosynthesis of V. natans thalli grown at 25 °C decreased compared with those of V. natans thalli grown at 18 °C. The RGR and photosynthetic rate of V. natans grown in the presence of increased carbon supply and high temperature were the lowest amongst the four different conditions. Therefore, the negative effects caused by a high temperature were pronounced under the condition of a global atmospheric CO2 increase.
Atmospheric carbon dioxide (CO2) concentration is expected to rise in the coming decades. Rising atmospheric CO2 levels may alter plant–herbivore insect associations primarily due to the indirect effects of CO2 enrichment on phytochemicals. Understanding the effects of elevated CO2 on major crop pests is a critical step for its early warning, forecasting, and integrative management. Our aims were to compare and examine the impacts of elevated CO2 on the belowground and aboveground associations such as leguminous plants with rhizobium, as well as legumes and phloem feeding insects. We aimed to approach the characteristics and mechanism of the response of different living organisms to elevated CO2, which provides the scientific evidence for integrated pest management in the future. Recent studies show that elevated CO2 alters leguminous plant resistance, nutritional value, and water status and that these changes affect certain feeding stages of aphids and subsequently influence the performance of aphids. We therefore suggest that the legumes may suffer greater damage from aphids if atmospheric CO2 levels continue to increase.
The evolution of adaptive interactions with beneficial, neutral and detrimental microbes was one of the key features enabling plant terrestrialization. Extensive studies have revealed conserved and unique molecular mechanisms underlying plant-microbe interactions across different plant species; however, most insights gleaned to date have been limited to seed plants. The liverwort Marchantia polymorpha, a descendant of early diverging land plants, is gaining in popularity as an advantageous model system to understand land plant evolution. However, studying evolutionary molecular plant-microbe interactions (EvoMPMI) in this model is hampered by the small number of pathogens known to infect M. polymorpha. Here, we describe four pathogenic fungal strains, Irpex lacteus MI1, Phaeophlebiopsis peniophoroides MI2, Bjerkandera adusta MI3, and Bjerkandera adusta MI4, isolated from diseased M. polymorpha. We demonstrate that salicylic acid (SA) treatment of M. polymorpha promotes infection of the I. lacteus MI1 that likely to adopt a necrotrophic lifestyle, while this effect is suppressed by co-treatment with the bioactive jasmonate in M. polymorpha, dinor-cis-12-oxo-phytodienoic acid (dn-cis-OPDA), suggesting that antagonistic interactions between SA and oxylipin pathways during plant-fungus interactions are ancient and were established already in liverworts.
In nature, chitin is the second most plentiful and renewable polysaccharide and is present among versatile group of organisms from fungi and nematodes to arthropods and crustaceans. Enzymatic degradation is the preferable environmentally safe mode of bioprocessing of this inert biopolymer. Chitin-scavenging enzyme-producing sources are covering the living groups from prokaryotes to plants, viruses, vertebrates, and even human. Current-day biotechnologies have raised the development of bioprocesses by using microbes especially bacteria. Bacteria that produce chitinases are with varieties of habitats ranging from Antarctic soil to hot spring, crustacean waste site, animal gut, and endophytic ecosystems. Chitin metabolism is a necessary life-supporting goings-on in agronomic plant pests like fungi, insects, and parasitic nematodes which are negatively proportionate to the agricultural production systems. Placement of such potent chitinolytic bacteria for plant fortification against attacking pests is a well-practiced, biotechnologically equipped biocontrol strategy. By-products of chitin by enzymatic hydrolysis, like oligomers or monomers, have several applications in persuading the plant defense systems. Carrying the host-defensive activity to biocontrol potentiality against plant pests, bacteria with chitinolytic property also behaved as a plant growth-promoting biofertilizing employee in modern-day sustainable agricultural practices. In this context, the distribution of chitinase-producing bacteria according to their diversity of habitats is studied, and the less explored habitats can be an arsenal for biocontrolling agents against plant pests.
Biotic interactions through diffusible and volatile organic compounds (VOCs) are frequent in nature. Soil bacteria are well-known producers of a wide range of volatile compounds (both organic and inorganic) with various biologically relevant activities. Since the last decade, they have been identified as natural biocontrol agents. Volatiles are airborne chemicals, which when released by bacteria, can trigger plant responses such as defence and growth promotion. In this study, we tested whether diffusible and volatile organic compounds (VOCs) produced by soil bacterial isolates exert anti-oomycete and plant growth-promoting effects. We also investigated the effects of inoculation with VOC-producing bacteria on the growth and development of Capsicum annuum and Arabidopsis thaliana seedlings. Our results demonstrate that organic VOCs emitted by bacterial antagonists negatively influence mycelial growth of the soil-borne phytopathogenic oomycete Phytophthora capsici by 35% in vitro. The bacteria showed plant growth promoting effects by stimulating biomass production, primary root growth and root hair development. Additionally, we provide evidence to suggest that these activities were deployed by the emission of either diffusible organic compounds or VOCs. Bacterial VOC profiles were obtained through solid phase microextraction (SPME) and analysis by gas chromatography coupled with mass spectrometry (GC–MS). This elucidated the main volatiles emitted by the isolates, which covered a wide range of aldehydes, alcohols, esters, carboxylic acids, and ketones. Collectively, twenty-five VOCs were identified to be produced by three bacteria; some being species-specific. Our data show that bacterial volatiles inhibits P. capsici in vitro and modulate both plant growth promotion and root system development. These results confirm the significance of soil bacteria and highlights that ways of harnessing them to improve plant growth, and as a biocontrol agent for soil-borne oomycetes through their volatile emissions deserve further investigation.
In ecology, plant–herbivore relationships are the crucial link generating animal biomass from mere sunlight
through photosynthesis. These interactions are basic in understanding ecology and evolution of virtually any
ecosystem. The relationship depends also on environmental factors like rainfall, temperature and altitude.
Understanding patterns of these environment-dependent interactions will help to make better predictions and
recommend possible conservation strategies. Many of existing mathematical models for plant–herbivore interactions
and their analysis do not include these environmental factors. In this study, a mathematical model that
incorporates variations of some of the parameter values due to changes in temperature and rainfall is formulated
and used to determine necessary threshold values for co-existence. To validate the results of the mathematical
model, real data from the Genale-Dawa river basin in the southern part of Ethiopia, is collected and used. The
river basin represents the three major climatic zones of the country, the cool zone, temperate zone and hot
lowlands. Numerical simulations were done using the collected data and it is observed that coexistence is
possible in all the three regions but it is sensitive to the change in rainfall and temperature. If the change is
within 10% there is a possibility of population extinction. Hence this paper shows that co-existence of population
is highly dependent on the environmental changes.
Elevated levels of atmospheric CO2 are predicted to contribute to major climatic changes during the next 50–100 years. This can have a significant impact on future food security if such changes make crop plants vulnerable to biotic and abiotic stresses. Indeed, a growing body of recent studies highlighted in this review show that elevated CO2 (eCO2) directly and/or indirectly influence plant-biotic interactions. In many instances, eCO2 alters phytohormone and reactive oxygen signalling, secondary metabolism as well as defence-associated development such as stomatal responses in the host. eCO2 can also directly and/or indirectly influence pathogenesis- and herbivory-related traits in pest and pathogen populations although currently very little is known about the molecular mechanisms involved in such effects. In addition, eCO2 alters predator-prey interactions by interfering with indirect defences and chemical communications in insect pests. A better understanding of molecular mechanisms involved in plant-biotic interactions under eCO2 will be critical towards mitigation of potentially adverse effects of climate change on crop production.
Plants are important nutrient source for several organisms like microbes, heterotrophic plants, insects as well as vertebrates. Even though they lack a proper defense mechanism like animals, still they have developed a mixture of chemicals which are mainly protein based and are used as a means of defense by detecting attacking organisms and preventing them from causing major damage. In order to protect themselves from these microbes like fungi, bacteria, etc., plant cells have developed the capability to identify attacking pathogens and use inducible defense mechanism by producing toxic chemicals or antimicrobial compounds in the form of pathogen-degrading enzymes and secondary metabolites involved with plant defense. Secondary metabolites generally are grouped into three major classes of chemicals, i.e. terpenoids, phenolic and alkaloids. Some of these antimicrobial compounds are constitutive in nature, i.e. they occur in biologically active forms in healthy plants, whereas other metabolites are inductive in nature. Glucosinolates and cyanogenic glycosides exist in inactive form and are activated as a response to attack by pathogen or tissue damage. These compounds are activated by release of plant enzymes at the time of breakdown of cells. Preformed antimicrobial compounds are termed as “phytoanticipin”, while “phytoalexins” are those antimicrobial compounds which are synthesized (as a result of synthesis of enzymes) from precursors as a response to attack by pathogen. Preformed inhibitors are usually tissue specific and are mainly present in the outer layers of the cells of plant organs. These inhibitors are mostly successful against comprehensive range of probable pathogens, and specific virulent pathogens might circumvent the effect of these secondary metabolites by eluding them or by enduring or by detoxification. Most of these constitutive plant compounds show antifungal activity, e.g. phenols, phenolic glycoside, unsaturated lactones, sulphur compounds, saponins, etc. “Phytoalexins” are the most considered antimicrobial plant defense compounds. These compounds are pathogen specific and therefore more effective in plant defense mechanism. Transcriptional and translational activities in a plant are prerequisite for the production of phytoalexins. Examples of these antimicrobial phytoalexins are scopoletin, camalexin, glucosinolates, etc. This chapter will mainly discuss the role of both phytoanticipins and phytoalexins as plant defense antimicrobial compounds and also their use as “antibiotic potentiators” and virulence attenuators along with their role in crop protection/phytoprotection.
Basella alba is a perennial plant of the Basellaceae and is known by various common names including Malabar spinach. There are few insects that cause damage to B. alba. In this study, we examined the effect of B. alba leaves on the growth of Spodoptera litura larvae. B. alba leaves and a methanolic extract of the leaves inhibited the growth of S. litura larvae. Half of the larvae reared on the leaves died within 1 week. We found that two flavonoids, vitexin, and vitexin-2″-O-arabinofuranoside, were abundant in the methanol extract of leaves. When larvae were reared on purified vitexin or vitexin-2″-O-arabinofuranoside, their growth was significantly impaired compared with larvae reared on control spinach leaves. These results suggested that the flavonoid glycosides in B. alba leaves act as deterrents to S. litura larvae.
Plants belonging to the genus Nepenthes are carnivorous, using specialized pitfall traps called "pitchers" that attract, capture and digest insects as a primary source of nutrients. We have used RNA sequencing to generate a cDNA library from the Nepenthes pitchers, and applied it to mass spectrometry-based identification of the enzymes secreted into the pitcher fluid, using a non-specific digestion strategy superior to trypsin in this application. This first complete catalog of the pitcher fluid sub-proteome includes enzymes across a variety of functional classes. The most abundant proteins present in the secreted fluid are proteases, nucleases, peroxidases, chitinases, a phosphatase and a glucanase. Nitrogen recovery involves a particularly rich complement of proteases. In addition to the two expected aspartic proteases, we discovered three novel nepenthensins, two prolyl endopeptidases that we name neprosins, and a putative serine carboxypeptidase. Additional proteins identified are relevant to pathogen-defense and secretion mechanisms. The full complement of acid-stable enzymes discovered in this study suggests that carnivory in the genus Nepenthes can be sustained by plant-based mechanisms alone, and does not absolutely require bacterial symbiosis.
Festuca grew faster in the 2-species mixture than in monoculture and Deschampsia grew more slowly, at 2 nutrient levels. Both root and shoot competition occurred, with root competition having the greater effect, but there was little interaction between them. Phosphorus was the major element most limiting to growth in the unfertilized soil, but there was little evidence of competition for it, presumed to be because of its low mobility in soil. -from Authors
The effect of two soil amendments of tannery sludge (10% and 20%) on growth and metal uptake of Helianthus annuus L. was studied under three treatments of rhizosphere and mycorrhizal fungi. Trichoderma pseudokoningii Rifai was used as rhizosphere fungal inoculum (F) and Glomus fasciculatum (Thax.) Gerd. & Trappe as the mycorrhizal inoculum (M). The third treatment comprised of combined inoculation (F+M). The control (C) treatment was without any inoculum of the fungi. The plants given both the fungus and mycorrhizal (F+M) treatment showed the maximum growth among all treatments. Plants given only fungus (F) and only mycorrhizal (M) treatment also showed significantly better growth as compared with control (C) treatment. Among the two sludge amendments, the statistical analyses of the results showed increase in all growth parameters in lower (10%) sludge amendment ratio. The accumulation of potentially toxic metals (Cd, Cr, Na and Zn) in different parts of H. annuus grown on tannery sludge amended soil increased with increasing concentration of sludge in the soil. The plants treated with both fungus and mycorrhizal (F+M) treatment showed the maximum uptake of metals and thus the synergistic effect of these fungi can be exploited in decontamination of metals from tannery sludge.
Red alder (Alnus rubra) and Sitka willow (Salix sitchensis) trees subjected to attack by tent caterpillars (Malacosoma californicum pluviale) or webworms (Hyphantria cunea), respectively, exhibited a change in foliage quality such that bioassay insects fed leaves from the attacked trees grew more slowly than those fed leaves from unattacked control trees. In contrast, bioassay of leaf quality of S. sitchensis, subjected to attack by tent caterpillars, indicated that altered leaf quality had been induced not only in the attacked trees but also in nearby unattacked control trees. This suggests that S. sitchensis is sensitive to and can respond to signals generated by attacked trees or the caterpillars. Since no evidence was found for root connections between attacked and control willows, the message may be transferred through airborne pheromonal substances.
