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Induction of LTP (lipid transfer protein) and Pal (phenylalanine ammonia-lyase) gene expression in rice roots colonized by the arbuscular mycorrhizal fungus Glomus mosseae
Abstract
The expression of a lipid transfer protein (LTP) gene is regulated in Oryza sativa roots in response to colonization by the mycorrhizal fungus Glomus mosseae. Transcript levels increased when the fungus forms appressoria and penetrates the root epidermis and decreased at the onset
of the intercellular colonization of the root cortex. The analysis of histochemical GUS staining in transgenic rice plants
carrying the Ltp/Gus construct confirm the induction of Ltp gene associated with fungal appressoria formation and penetration area. The induction of Ltp gene expression coincided in time with a transient increase in the expression of a phenylalanine ammonia‐lyase (Pal) gene and a transient accumulation of salicylic acid (SA) in the mycorrhizal roots. The expression of Ltp and Pal was induced in rice roots after treatment with SA and Pseudomonas syringae indicating that both genes could be implicated in the plant defence response. The exogenous application of SA to rice interacting
with the mycorrhizal fungus did not affect appressoria formation but, instead, resulted in a transient delay of root mycorrhization.
Nevertheless, although Ltp maintained a prolonged SA‐induced expression level, mycorrhizal formation could still proceed.
... Subsequently, the fungus enters the root epidermis towards the inner cortex by forming entry points, forming hyphopodia, and stabilizes through host-derived cutin or cutin precursors (Wang et al., 2012;Bonfante and Genre, 2010). At this stage, other hormones such as SA play a positive role but in a dose-dependent manner, for example, the application of SA in rice did not inhibit hyphopodium formation (Blilou et al., 2000). In sequence, PPA where hyphae penetrate the root epidermis layer and restructure the plant root epidermis cell (Genre et al., 2005) which further differentiate into the root surface to form appressoria (Akiyama et al., 2005;Besserer et al., 2006). ...
... One of the studies where SA application inhibited root colonization by G. intraradices and G. mosseae inoculated plants (Herrera-Medina et al., 2003). The exogenous application of SA in rice works in a dose-dependent manner even low concentration inhibits root colonization but does not inhibit hyphopodia formation (Blilou et al., 2000). This was due to the SA marker gene PATHOGENESISRELATED10 (PR10) induced in root cells close to hyphopodia which suppresses the fungal entry into the root during the fungal formation of the PPA (Siciliano et al., 2007;Gutjahr and Paszkowski, 2009). ...
... This was due to the SA marker gene PATHOGENESISRELATED10 (PR10) induced in root cells close to hyphopodia which suppresses the fungal entry into the root during the fungal formation of the PPA (Siciliano et al., 2007;Gutjahr and Paszkowski, 2009). Although SA exogenous application showed reduced mycorrhizal development, at the early stage of symbiosis least during the first weeks (Blilou et al., 2000;Costa et al., 2000;Özgönen et al., 2001;de Roman et al., 2011). This certainly performs, with a short-lived rise in SA levels during the early stages of AM colonization (Blilou et al., 1999). ...
Arbuscular mycorrhizal fungi (AMF), the most common association form a symbiotic association with more than 80% of land plants. During AMF symbiosis, fungal hyphae and root cells exchange signal molecules. Phytohormones are biostimulants that stimulate host roots and influence AMF development. Phytohormones regulate the presymbiotic stage of AMF from the early recognition of events up to the formation of arbuscular, hyphal branching and consequently influence arbuscular mycorrhizal (AM) intra and extra-radical hyphae and spore formation. The crucial roles of numerous phytohormones, such as auxins, cytokinins, gibberellins, etc., in the modulation of AM symbiosis, have been known. However, new generation phytohormones such as strigolactones, salicylates (salicylic acid), brassinosteroids, and jasmonic acid are involved in the recognition and regulation of fungal growth are needed to be explicated. The hypothesis is that some phytohormones promote AMF formation in situ and consequently the synergistic effect may stimulate plant growth. In this chapter, we provided the current status of the role of these plant hormones on AMF and associated mechanisms involved in the regulation of AM symbiosis.
... Numerous studies indicate that in the plant host/Arbuscular mycorrhiza fungi (AMF) interaction, plant defense responses are induced during early root colonization and are repressed subsequently [57,58]. A transient accumulation of SA during the first stage of AM root colonization, associated with the early induction of plant defense responses, has been reported [59,60]. The role of SA in the regulation of root colonization has been suggested during the establishment of the AM symbiosis. ...
... Indeed, the inability of Myc -Pisum sativum mutants to form the AM association was linked to enhanced SA level during the early steps of the interaction [61]. Rhizobium leguminosarum Pisum sativum [77,78] Sinorhizobium meliloti Medicago truncatula [79] Moreover, SA exogenously applied to roots in AMF-rice interaction reduced root colonization at the early stages of the interaction [59]. However, no effect of SA on AMF appressoria formation was observed [59]. ...
... Rhizobium leguminosarum Pisum sativum [77,78] Sinorhizobium meliloti Medicago truncatula [79] Moreover, SA exogenously applied to roots in AMF-rice interaction reduced root colonization at the early stages of the interaction [59]. However, no effect of SA on AMF appressoria formation was observed [59]. Application of SA to leaves of cucumber plants showed no effect on the interaction with AMF excluding its systemic effect on the symbiotic interaction [80]. ...
Plants form beneficial symbioses with a wide variety of microorganisms. Among these, endophytes, arbuscular mycorrhizal fungi (AMF), and nitrogen-fixing rhizobia are some of the most studied and well understood symbiotic interactions. These symbiotic microorganisms promote plant nutrition and growth. In exchange, they receive the carbon and metabolites necessary for their development and multiplication. In addition to their role in plant growth and development, these microorganisms enhance host plant tolerance to a wide range of environmental stress. Multiple studies have shown that these microorganisms modulate the phytohormone metabolism in the host plant. Among the phytohormones involved in the plant defense response against biotic environment, salicylic acid (SA) plays an important role in activating plant defense. However, in addition to being a major actor in plant defense signaling against pathogens, SA has also been shown to be involved in plant–microbe symbiotic interactions. In this review, we summarize the impact of SA on the symbiotic interactions. In addition, we give an overview of the impact of the endophytes, AMF, and rhizobacteria on SA-mediated defense response against pathogens.
... During the early stage of AM fungi symbiosis development, stimulation of antioxidant enzymes was noticed by several workers (Blilou, Ocampo, and Garcia-Garrido 2000;Hajiboland and Joudmand 2009). The stimulation of ROS-scavenging enzymes, such as POD, polyphenol oxidase, catalase and superoxide dismutase is the key mechanism to scavenge detrimental ROS during stress conditions (Evelin and Kapoor 2014). ...
... Several reports were already mentioned the increase in PPO activity in AM inoculated plants (Tang, Chen, and Shang 2000;Nelson and Achar 2001;Panwar and Vyas 2002). There is also a view that alteration in the pattern of antioxidative enzymes such as PPO in mycorrhizal roots may indicate that oxidative components are produced during initial phase of colonization (Blilou, Ocampo, and Garcia-Garrido 2000). ...
Arbuscular mycorrhizal (AM) fungi are one of most important soil microorganisms that can form mycorrhizal symbiosis with most of the terrestrial plants. In the present study, the effect of arbuscular mycorrhizal fungi inoculation on root colonization, growth, nutrition, photosynthetic gas exchange and antioxidant activities of black pepper cuttings were evaluated under polyhouse conditions. The single node cuttings of black pepper were grown in the presence and absence of AM combinations for 150 days under poly house. AM inoculated plants showed significantly higher mycorrhizal root colonization (95%) and spore numbers (312/50 g of sample). The effect of AM fungi was more prominent in improving root biomass than above ground biomass. Nutrient accumulations were higher in AM inoculated plants rather than uninoculated black pepper plants. Amount of acid phosphatase and dehydrogenase activity were significantly higher in AM inoculated soils. Net photosynthetic rate and stomatal conductance of AM colonized black pepper leaves were found to be significantly greater than uninoculated plants. The influence of AM was more prominent on poly phenol oxidase and β-glucanase activity in leaves than roots. In principal component analysis the scatter plot revealed variations of the effects of arbuscular mycorrhizal fungi on growth of black pepper cuttings. Based on these results, AM inoculation at the earlier stage of plant development could improve symbiosis, and increased plant growth in the nursery which may improve the performance after planting in the field.
... They maintain cell function and mediating responses to stress during plant growth and development. Furthermore, the LTP could activate the plant phenylpropanoid pathway genes [7] that they defend against free radicals and may also provide tolerance to a wide array of stresses. Not only LTPs are involved in stress conditions, but they were also transiently expressed during the inoculation process [4]. ...
... In the inoculation of Oryza sativa roots with mycorrhizal, the expression of LTP and Pal was increased, these genes are involved in the plant response to the environment stress [7]. This simply means that PGPRs can affect the expression of stress-responsive genes and modulate plant responses to stress. ...
Azospirillum brasilense may regulate MN052803-LTP expression and the activity of defensiveenzymes in wheat (Triticum aestivum L.) cultivars to improve salinity tolerance. In a primary experiment, ger-mination indexes of 18 wheat cultivars were measured and Sorkhtokhm and Qods were selected as tolerantand sensitive cultivars to salinity, respectively. Selected cultivars inoculated with A. brasilense (Sp245 producemore ABA and Sp7 as standard strain) and grown-up to five days, then salinity (200 mM NaCl) was appliedto seedling via Hoagland’s nutrient solution. The relative expression of MN052803-LTP (authors recorded inthe Gen Bank) of roots and shoots was measured at 12, 24, and 48 hours after salinity applied. The resultsshowed that MN052803-LTP expression increased in the order of salinity, inoculation, and inoculation plussalinity. Meanwhile, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) activityincreased in the same order in 12 days-old seedlings. In a similar experiment, 10 mM dithiothreitol (DTT)was used as a reducer and inoculation as a stimulator of MN052803-LTP expression, then the relative expres-sion and phosphatidylcholines (PC) content were measured. Although the MN052803-LTP expression andPC was reduced due to the application of DTT, inoculation eliminates its inhibitory effect. The highestamount of PC was observed in inoculated plants, and the lowest in the plants treated with DTT. Probably,A. brasilense improves salt tolerance of wheat cultivars through MN052803-LTP expression, and PC contentvia repairing the membrane damages by supplying the membrane phospholipids, such as phosphatidylcho-line, and accumulation of antioxidant compounds by activating PAL and TAL via membrane lipid-dependentsignaling cascades
(PDF) Azospirillum brasilense Can Modulate Salt Stress in Triticum aestivum via MN052803-LTP Regulation and Phosphatidylcholines Content. Available from: https://www.researchgate.net/publication/353961954_Azospirillum_brasilense_Can_Modulate_Salt_Stress_in_Triticum_aestivum_via_MN052803-LTP_Regulation_and_Phosphatidylcholines_Content [accessed Oct 22 2022].
... Various biotic stresses increase the activity of PAL, the first enzyme in the phenylpropanoid pathway (Blilou et al. 2000;Derksen et al. 2013). Contrastingly, in our sugar beet plants, PAL activity was not influenced by the +AMF treatment. ...
... Because AMF are obligate biotrophs and share similarities with biotrophic pathogens (Pozo and Azcón-Aguilar 2007), the involvement of SA in the defense mechanisms of nonhost plant species against AMF is likely, but unexplored. The accumulation of SA upon AMF treatment (Poveda et al. 2019;Fernández et al. 2019) and a transitory delay of root mycorrhization by exogenous SA (Blilou et al. 2000) suggest a key role for SA in the incompatible response to AMF (Poveda et al. 2019). In our sugar beet, in contrast, the opposite was observed and a significant reduction of SA concentration and exudation upon +AMF treatment showed a distinct difference between the incompatible AMF response in sugar beet with the typical hypersensitive response. ...
The interactions between arbuscular mycorrhizal fungi (AMF) and non-host species are poorly studied. Particularly scarce is information on members of the Amaranthaceae/Chenopodiaceae family. Sugar beet (Beta vulgaris) plants were co-cultivated with a host species (Hordeum vulgare) in the presence (+AMF) or absence of Rhizophagus intraradices to explore the hypothesis that the presence of an active, pre-established AMF mycelium induces defense responses in the non-host species. Biomass of sugar beet did not respond to the +AMF treatment, while its root exudation of organic acids and phenolic acids was drastically decreased upon co-cultivation with +AMF barley. The most conspicuous effect was observed on a wide range of potential defense parameters being differentially influenced by the +AMF treatment in this non-host species. Antioxidant defense enzymes were activated and the level of endogenous jasmonic acid was elevated accompanied by nitric oxide accumulation and lignin deposition in the roots after long-term +AMF treatment. In contrast, significant reductions in the levels of endogenous salicylic acid and tissue concentration and exudation of phenolic acids indicated that AM fungus hyphae in the substrate did not induce a hypersensitive-type response in the sugar beet roots and downregulated certain chemical defenses. Our results imply that the fitness of this non-host species is not reduced when grown in the presence of an AMF mycelium because of balanced defense costs. Further studies should address the question of whether or not such modulation of defense pattern influences the pest resistance of sugar beet plants under field conditions.
... It also appears to inhibit colonization by biotrophic AMF as transgenic tobacco plants with constitutive salicylic acid synthesis (CSA) showed reduced root colonization, while those with reduced SA levels due to expression of the SA hydroxylase NahG showed enhanced colonization (Herrera-Medina et al. 2003). In nontransgenic rice plants, SA transiently accumulated at five days post inoculation with AMF (Blilou et al. 2000) and this may coincide with the early and transient induction of defense genes that has been observed in inoculated M. truncatula roots (Liu et al. 2003). Congruously, the SA marker gene PATHOGENESIS-RELATED 10 (PR10) was induced in cells close to hyphopodia but reduced again during fungal passage of the PPA (Siciliano et al. 2007). ...
... Congruously, the SA marker gene PATHOGENESIS-RELATED 10 (PR10) was induced in cells close to hyphopodia but reduced again during fungal passage of the PPA (Siciliano et al. 2007). Application of SA to rice inhibited colonization in a dose-dependent manner but did not inhibit hyphopodium formation (Blilou et al. 2000). It is possible that SA suppresses fungal entry into the root for example during the formation of the PPA (Gutjahr and Paszkowski 2009). ...
Arbuscular mycorrhiza (AM) is one of the most prominent symbiotic associations in nature. It involves arbuscular mycorrhiza fungi (AMF) of the Glomeromycotina and land plants and acts as a nutrient acquisition strategy for plants. An important process for the development of this association is the exchange of chemical signals between the symbionts and the accommodation of AMF inside the plant roots, for which the root cells undergo dramatic developmental changes. Plant hormones are important determinants of the balance between plant development, nutrition and stress response and their regulatory role in the establishment of AM symbiosis is an area of active research. This chapter summarizes and discusses the current knowledge on the role of phytohormones in AM development.
... The metabolism of phenolic protective substances is differently impressed by various environmental and stress factors (Sakihama et al., 2002). It has been determined that, SiO 2 NP stimulates the production of precursors, which leads to increased protein levels in plant cells and finally induce the expression of genes related to valuable metabolite production including phenolic compounds (Blilou et al., 2000). Furthermore, elicitor concentration and exposure time are critical factors in the elicitation process. ...
... A positive association was found between pal expression and RA production in elicited-hairy roots with SiO 2 NP. SiO 2 increased the activity of PAL enzyme, which catalyzes the deamination of phenylalanine to precursors for phenolic compounds production (Blilou et al., 2000). The rapid increase of PAL activity during the elicitation of RA accumulation observed in previous studies (Sumaryono et al., 1991;Mizukami et al., 1993;Szabo et al., 1999). ...
Dracocephalum kotschyi Boiss. is one of the important threatened traditional species of medicinal herbs; last pharmaceutical research has shown that rosmarinic acid (RA) and methoxylated flavonoids, particularly, xanthomicrol and cirsimaritin of this plant have anti-cancer, anti-spasm and anti-platelet properties. In this study, Hairy roots were derived from four-week-old leaves inoculated with Agrobacterium rhizogenes strain ATCC15834. The influence of various silicon dioxide nanoparticles (SiO2 NPs) concentrations at two exposure time (24 and 48 h) on growth, antioxidant enzyme capacity, total phenols and flavonoids content (TPC and TFC) and some biochemical traits were investigated. The expression of phenylalanine ammonia-lyase (pal) and rosmarinic acid synthase (ras) genes expression in RA biosynthetic pathway were quantified. The biomass of cultures has substantially by elicitation raised in comparison with control. The activity of antioxidant enzymes, TPC and TFC were impressed by the concentration and duration of treatment. The high RA content (1016.6 μg/g FW) with 8.26-fold increase compared to control, was observed in hairy roots culture elicited with SiO2 NPs (100 mg/L) after 48 h exposure time. The pal and ras genes expression rate in this elicitor concentration and exposure time enhanced notably. Anticancer flavonoids including xanthomicrol, cirsimaritin and isokaempferide showed 13, 13.42 and 10-fold increases compared to the control respectively. Stimulation of D. kotschyi hairy roots by SiO2 NPs caused huge increase in induction and production of important pharmaceutical compounds such as rosmarinic acid and xantomicrol.
... AMFcolonized rice was found to have induced lipid transfer protein (encoded from Ltp gene) (Blilou et al., 2000b.) which is accountable for plant defence response for its antimicrobial property (Molina and García-Olmedo, 1993;García-Olmedo, 1995). ...
... which is accountable for plant defence response for its antimicrobial property (Molina and García-Olmedo, 1993;García-Olmedo, 1995). Phenylalanine ammonia lyase (PAL) enzyme (encoded from Pal gene), which leads to the production of phytoalexins and phenolic compounds, was also persuaded in the rice infected with AMF (Blilou et al., 2000b.). In addition to this, VCH3 gene-encoded chitinase enzyme was observed in the primed expression of AMFcolonized grapevine roots against Meloidogyne incognita (Li et al., 2006). ...
Arbuscular mycorrhizal fungi (AMF), the ancient mutualist and biotroph of plants,
improve the supply of water and nutrients, such as phosphate and nitrogen to its host
plant. In exchange of this, it takes a part of photosynthate sugar to complete its life cycle.
Despite having its own immune system, the plant upon pathogen attack gets weaken and
needs reinforcement to fight back and become stabilize in the battle ground. AMF fulfills
the need of host plant and provides with support in many ways by induction of
attenuated defence signaling for combating against phytopathogen. This elevation not
only makes plant more tolerant towards the attack of phytopathogen but also, enhances
the genetic, biochemical and signaling factors responsible for its defence purpose. In this
article, we look forward to discuss the factors, mechanisms and pathways responsible for
this back-up from AMF to plants with recent experimental proof. In addition, this meta-analysis
will also try to focus on areas that have recently got attention or are less known,
so that, lacunae and underestimated aspects should come in front for a further systematic
research.
... However, using mutants with higher sensitivity to ET, it has been shown that ET may mitigate the inhibitory effect of Pi on the AM association (Torres Santos et al. 2016) Have a role during AM symbiosis; the tomato biosynthetic mutant (dX) exhibits a lower level of AM colonization (Bitterlich et al. 2014). BR acts likely through inhibition of plant defense or upregulation of invertase (Lin6) (Bitterlich et al. 2014), which is involved in the provision of hexoses to the fungus (Schaarschmidt et al. 2006) Salicylic acid (SA) Exogenous application of SA decreases the root colonization at the beginning of the AMF-plant interaction but fails to affect the formation of appressoria (Blilou et al. 2000). The AM-defective (Myc -) mutants show higher SA accumulation compared with wild (Myc + ) plants (Blilou et al. 1999). ...
The most prevalent microorganism association in terrestrial plants is the symbiosis between arbuscular mycorrhizal fungi (AMF) and plant roots. This implies that the genetic background for establishing this symbiosis was developed in the early phases of land plant evolution. A symbiosis faces several challenges, such as penetrating plant cells and overcoming their defense mechanisms. At the same time, it must activate some developmental pathways for symbiotic structures along with membrane transporters required to exchange nutrients and metabolites between two partners. This chapter discusses the response of plants to fungal signals, the function of receptor molecules, and other actors that play a crucial role in the signaling pathways. Ultimately, these pathways result in the expression of symbiosis-specific genes and the formation of symbiosis-specific structures.
... Only one publication reports the overexpression of a gene encoding nsLTPs in Oryza sativa roots during appressoria formation and penetration of the mycorrhizal fungus Glomus mosseae. This gene is subsequently down-regulated upon mycorrhization, during the intracellular development of fungal hyphae in the root and is also induced upon treatment with salicylic acid or with the pathogen Pseudomonas syringae indicating that this nsLTP is not involved in mycorrhization but probably part of the plant's defense system 38 . In M. truncatula, two nsLTPs (MtnsLTP104 and MtnsLTP103 corresponding to Medtr4g077180 and Medtr4g076150; respectively) are up-regulated during mycorrhizal symbiosis with the arbuscular mycorrhizal fungi Rhizophagus irregularis but no functional studies have been performed. ...
Non-specific lipid transfer proteins (nsLTPs) are antimicrobial peptides, involved in several plant biological processes including root nodule nitrogen fixation (RNF). Nodulating plants belonging to the RNF clade establish symbiosis with the nitrogen-fixing bacteria rhizobia (legumes symbiosis model) and Frankia (actinorhizal symbiosis model) leading to root nodule formation. nsLTPs are involved in processes active in early step of symbiosis and functional nodule in both models. In legumes, nsLTPs have been shown to regulate symbiont entry, promote root cortex infection, membrane biosynthesis, and improve symbiosis efficiency. More recently, a nsLTP, AgLTP24 has been described in the context of actinorhizal symbiosis between Alnus glutinosa and Frankia alni ACN14a. AgLTP24 is secreted at an early step of symbiosis on the deformed root hairs and targets the symbiont in the nitrogen-fixing vesicles in functional nodules. nsLTPs are involved in RNF, but their functions and evolutionary history are still largely unknown. Numerous putative nsLTPs were found up-regulated in functional nodules compared to non-infected roots in different lineages within the RNF clade. Here, results highlight that nodulating plants that are co-evolving with their nitrogen-fixing symbionts appear to have independently specialized nsLTPs for this interaction, suggesting a possible convergence of function, which opens perspectives to investigate nsLTPs functions in RNF.
... Expression of a lipid transfer protein gene was up-regulated in rice roots in response to colonization of G. mosseae. Blilou et al. (2000) G. intraradices More than 200 genes were modulated upon inoculation of rice roots with G. intraradices. Some of the genes that responded to G. intraradices colonization were involved in the uptake of phosphate. ...
The system of rice intensification (SRI) is an extensively-researched and increasingly widely-utilized methodology for alleviating current constraints on rice production. Many studies have shown physiological and morphological improvements in rice plants induced by SRI management practices to be very similar to those that are associated with the presence of beneficial microbial endophytes in or around rice plants, especially their roots. With SRI methods, grain yields are increased by 25-100% compared to conventional methods, and the resulting plant phenotypes are better able to cope with biotic and abiotic stresses. SRI management practices have been shown to be associated with significant increases in the populations of certain microorganisms known to enhance soil health and plant growth, e.g., Azospirillum, Trichoderma, Glomus, and Pseudomonas. This article evaluates the effects of applying Trichoderma as a model microbe for assessing microbial growth-promotion, biological control activity, and modulation of gene expression under the conditions created by SRI practices. Information about the molecular changes and interactions associated with certain effects of SRI management suggests that these practices are enhancing rice plants’ expression of their genetic potentials. More systematic studies that assess the effects of SRI methods respectively and collectively, compared with standard rice production methods, are needed to develop a more encompassing understanding of how SRI modifications of crops’ growing environment elicit and contribute to more robust and more productive phenotypes of rice.
... In several land plant species, SA levels are induced during interactions with beneficial microbes (Blilou et al., 1999(Blilou et al., , 2000Liu et al., 2003;Pozo et al., 2015). Further cyanobacterial treatment of A. thaliana resulted in the induction of SA controlled gene expression (Belton et al., 2021). ...
Despite its small size, the water fern Azolla is a giant among plant symbioses. Within each of its leaflets, a specialized leaf cavity is home to a population of nitrogen-fixing cyanobacteria (cyanobionts). Although a number of plant-cyanobiont symbioses exist, Azolla is unique in that its symbiosis is perpetual: the cyanobionts are inherited during sexual and vegetative propagation. What underpins the communication between the two partners? In angiosperms, the phytohormone salicylic acid (SA) is a well-known regulator of plant-microbe interactions. Using high-performance liquid chromatography-tandem mass spectrometry, we pinpoint the presence of SA in the fern. Comparative genomics and phylogenetics on SA biosynthesis genes across Chloroplastida reveal that the entire Phenylalanine ammonia-lyase-dependent pathway likely existed in the last common ancestor of land plants. Indeed, Azolla filiculoides secondarily lost its isochorismate synthase but has the genetic competence to derive SA from benzoic acid; the presence of SA in artificially cyanobiont-free Azolla supports the existence of this route. Global gene expression data and SA levels from cyanobiont-containing and -free A. filiculoides link SA synthesis with the symbioses: SA appears to induce cyanobacterial proliferation, whereas removal of the symbiont results in reduced SA levels in a nitrogen-dependent manner.
... AM colonization changes the activities of both enzymes ( e.g., catalase and superoxide dismutase). Phenylalanine ammonia lyase ( PAL) is responsible for the production of phytoalexins and phenolic compounds in rice ( Blilou et al., 2000). ...
... AM colonization changes the activities of both enzymes ( e.g., catalase and superoxide dismutase). Phenylalanine ammonia lyase ( PAL) is responsible for the production of phytoalexins and phenolic compounds in rice ( Blilou et al., 2000). ...
... Therefore, AM as an obligate biotroph is expected to be negatively affected by SA. SA has indeed been shown to have a temporary negative effect on fungal root colonization in previous studies (Hause et al., 2007;Blilou et al., 2000). However, there are conflicting results reported regarding SA concentration in well-established associations. ...
Phytohormones are supposed to contribute to the establishment of mutualistic Arbuscular mycorrhiza (AM) symbioses. However, their role in the acclimation of micropropagated plantlet inoculated with AM is still unknown. To address this question, we performed a hormone profiling during the acclimation of Satureja khuzistanica plantlets inoculated with Rhizoglomus fasciculatum. The levels of indoleacetic acid (IAA), methyl indole acetic acid, cis-zeatin, cis zeatin ribose, jasmonate, jasmonoyl isoleucine, salicylic acid, abscisic acid (ABA) were analyzed. Further, the relative gene expression of AOS (Allene oxide synthase) as a key enzyme of jasmonate biosynthesis, in either inoculated or non-inoculated micropropagated plantlets was evaluated during acclimation period. The concentrations of IAA and cis-zeatin increased in the plantlets inoculated by AM whereas the concentration of ABA decreased upon 60 days acclimation in the whole shoot of plantlets of S. khuzistanica. The relative expression of AOS gene resulted in an increase of isoleucine jasmonate, the bioactive form of jasmonate. Based on our results, IAA and cis-zeatin probably contribute to maintaining growth, and AM reduces transition stress by modifying ABA and jasmonate concentrations.
... Similarly, isoflavone reductase and phenylalanine ammonia-lyase (PAL) genes were differentially expressed during interactions with A. brasilense and H. seropedicae. These genes are also expressed during the early stages of legume-rhizobia symbiosis and AM symbiosis (Blilou et al., 2000;Chen et al., 2017b). Some flavonoid genes were also differentially expressed in wheat roots colonized by A. brasilense (Camilios-Neto et al., 2014). ...
Major crops such as corn, wheat, and rice can benefit from interactions with various plant growth-promoting bacteria (PGPB). Naturally, several studies have investigated the primary mechanisms by which these PGPB promote plant growth. These mechanisms involve biological nitrogen fixation, phytohormone synthesis, protection against biotic and abiotic stresses, etc. Decades of genetic and biochemical studies in the legume-rhizobia symbiosis and arbuscular mycorrhizal symbiosis have identified a few key plant and microbial signals regulating these symbioses. Furthermore, genetic studies in legumes have identified the host genetic pathways controlling these symbioses. But, the same depth of information does not exist for the interactions between host plants and PGPB. For instance, our knowledge of the host genes and the pathways involved in these interactions is very poor. However, some transcriptomic studies have investigated the regulation of gene expression in host plants during these interactions in recent years. In this review, we discuss some of the major findings from these studies and discuss what lies ahead. Identifying the genetic pathway(s) regulating these plant-PGPB interactions will be important as we explore ways to improve crop production sustainably.
... It has antifungal activity both in vitro and in vivo and it works as penetrating the fungal membrane and finally causes cell death (Narasimhan et al., 2005). The defensive role of plant LTPs is their ability to inhibit fungal pathogens (Blilou et al., 2000). Antifungal tests of LTP protein isolated from sunflower demonstrated that it exerts a fungistatic effect (Regente and De La Canal, 2000). ...
Antifungal agents are causing different problems in the agriculture industry. Plants are using various defense mechanisms for resistance against fungal pathogens. Some examples of these mechanisms are making physical barriers, producing chemical components and pathogenesis-related proteins such as lipid transfer protein (LTP) and Osmotin which can inhibit the growth of fungi at micro-molar concentrations. In this study, Osmotin and LTP genes were fused by the EAAAK linker to produce a single-fused gene construct. An in silico approach was used to predict and analyze Osmotin-EAAAK-LTP fused protein. Secondary and tertiary structure and mRNA formation of fused protein were predicted using bioinformatics tools. The designed construct was chemically synthesized and cloned in the pUC57 cloning vector. To express the fused protein gene was subcloned in expression vector pET-21b (+) with a hexahistidine tag. This gene was used for prokaryotic expression in E. coli BL21 (DE3) host. Different expression conditions were examined for expressing of fused protein. The fused protein was expressed with 1 mM IPTG after 3 hours of incubation at 28°C. The expression of 36.5 kDa protein was confirmed by western blotting. The study of antifungal activity of expressed fused protein was achieved by radial diffusion assay. This protein was able to exhibit antifungal activity towards experimented plant pathogenic fungi under in vitro conditions. 2015 UMZ. All rights reserved.
... On the other hand, decreased SA concentrations due to SA hydroxylase activity promoted the colonization [102]. Like ABA, SA reduces mycorrhizal colonization in rice, although no observable effects on hyphopodium development have been reported [103]. Additionally, the SA introduction into rice effects the efficiency of fungal association by lowering the colonization in roots without disturbing the development of appressorium, which indicates indirect influence of SA on fungal growth [6]. ...
Modern agriculture is currently enduring rapid changes in defiance of the continuing increase of the global population and the various consequent environmental challenges. Crop quality is becoming as important as crop yield and can be characterized by several parameters. Extensive use of chemical fertilizers leads to food safety concerns globally; hence, the use of mycorrhizal symbionts have proven to be beneficial for the sustainable growth of the agricultural cropping system. Microflora inhabiting the soil entails various ecological interactions which are associated with agricultural performances. Amongst these microflora, mycorrhizal fungi are the critical suppliers of nutrients, with restricted diffusion capacities of minerals such as phosphorus, nitrate, zinc, sulfur etc. Mycorrhizae are the obligatory biotrophs that depend upon their host plant for the nutritional requirements. They act as the key contributors to sustainable agro-ecological enforcement and impact globally on the eco-systemic processes. These soil inhabitants devote themselves to the continuous nutrient flow and extemporize resistance against various environmental stresses like drought, flood, metal toxicity, salinity, etc. This review briefly highlights the taxonomic co-evolution, factors affecting mycorrhizal behaviors (phytohormonal regulation), and the concise mechanistic approach (improved water status, photosystems, stomatal conductance, ionic uptake, C & N fixation) to combat various environmental stresses (biotic/abiotic). Plant growth regulators play a crucial role in this symbiotic establishment with the plant roots. Auxins, brassinosteroids, and strigolactones are responsible for the establishment of mycorrhizal association. On the other hand, ethylene, abscisic acid, and jasmonic acids can promote or downregulate this process in the plants. Whereas, gibberellic acids and salicylic acids negatively impact on mycorrhizal association. The hormonal homeostasis (in response to fungal associations) leads to the activation of transcriptional and signaling cascades which ensues various physio-morphological changes for the benefit of the plant. The role of phytohormones in the regulation of plant-fungus mutualism, and the impact of mycorrhization on the activation of molecular and transcriptional cascades, have been described along with the potential applications of agricultural produce and soil rehabilitation.
... One study in Phaseolus vulgaris showed that transcript levels of an isoflavone reductase increased in roots during the early stages of interaction with Rhizobium etli 38 . Phenylalanine ammonia lyase (PAL) plays an important role in the biosynthesis of secondary plant metabolites, and PAL genes have been shown to be upregulated in expression during the early stages of arbuscular mycorrhizal symbiosis and legume-rhizobia symbiosis 39,40 . In this study, we observed two PAL genes (LOC_Os04g43800 and LOC_Os12g33610) that were upregulated in expression in rice roots. ...
Non-legume plants such as rice and maize can form beneficial associations with plant growth-promoting bacteria (PGPB) such as Herbaspirillum seropedicae and Azospirillum brasilense. Several studies have shown that these PGPB promote plant growth via multiple mechanisms. Our current understanding of the molecular aspects and signaling between plants like rice and PGPB like Herbaspirillum seropedicae is limited. In this study, we used an experimental system where H. seropedicae could colonize the plant roots and promote growth in wild-type rice. Using this experimental setup, we identified 1688 differentially expressed genes (DEGs) in rice roots, 1 day post-inoculation (dpi) with H. seropedicae. Several of these DEGs encode proteins involved in the flavonoid biosynthetic pathway, defense, hormone signaling pathways, and nitrate and sugar transport. We validated the expression pattern of some genes via RT-PCR. Next, we compared the DEGs identified in this study to those we previously identified in rice roots during associations with another PGPB, Azospirillum brasilense. We identified 628 genes that were differentially expressed during both associations. The expression pattern of these genes suggests that some of these are likely to play a significant role(s) during associations with both H. seropedicae and A. brasilense and are excellent targets for future studies.
... In this work we analysed the expression of the HaLTP gene family in different organs and under different stimuli. We observed that sunflower LTP genes were mainly activated in the seeds, stamens, and roots, as already reported in other plant species, including barley and rice [11,12,34]. However, genes belonging to different HaLTP groups were far more expressed in some organs than in others, such as Group 1 genes in the stamen and Group 3 genes in the roots ( Figure 5). ...
The sunflower (Helianthus annuus L.) is among the most widely cultivated crops in the world due to the oilseed production. Lipid transfer proteins (LTPs) are low molecular mass proteins encoded by a broad multigenic family in higher plants, showing a vast range of functions; these proteins have not been characterised in sunflower at the genomic level. In this work, we exploited the reliable genome sequence of sunflower to identify and characterise the LTP multigenic family in H. annuus. Overall, 101 sunflower putative LTP genes were identified using a homology search and the HMM algorithm. The selected sequences were characterised through phylogenetic analysis, exon–intron organisation, and protein structural motifs. Sunflower LTPs were subdivided into four clades, reflecting their genomic and structural organisation. This gene family was further investigated by analysing the possible duplication origin of genes, which showed the prevalence of tandem and whole genome duplication events, a result that is in line with polyploidisation events that occurred during sunflower genome evolution. Furthermore, LTP gene expression was evaluated on cDNA libraries constructed on six sunflower tissues (leaf, root, ligule, seed, stamen, and pistil) and from roots treated with stimuli mimicking biotic and abiotic stress. Genes encoding LTPs belonging to three out of four clades responded specifically to external stimuli, especially to abscisic acid, auxin, and the saline environment. Interestingly, genes encoding proteins belonging to one clade were expressed exclusively in sunflower seeds. This work is a first attempt of genome-wide identification and characterisation of the LTP multigenic family in a plant species.
... SA in coordination with endophyte activity decreased the level of ROS by enhancing polyphenol content to reduce peroxidase (POD), CAT, and GSH during osmotic stress in Capsicum annum (Khan et al., 2013). In rice, elevated levels of SA in addition to defense proteins were observed in the initial phase of infection with Glomus mosseae (Blilou et al., 2000). Gilmaniella sp., a fungal endophyte of A. lancea stimulated SA and promoted the production of volatile oil (Wang et al., 2011). ...
Endophytes are the microorganisms that exist inside the plant tissue without triggering any negative effects. Endophytes demonstrate a positive effect on plant growth and crop yield and are hence, highly important for agriculture. Endophytic fungi have the potential to reduce the need for fertilizers inducing a significant increase in seed germination, seedling vigor, biomass production, root hair development, plant photosynthetic efficiency, and crop yield. Fungal endophytes can improve plant biochemical composition by providing antioxidant defenses, osmoregulation, and influencing nutrient uptake efficiency during extreme conditions of the environment. The symbiotic relationship of endophytic fungi with crops can be an effective strategy to overcome the adverse effects of both abiotic and biotic stresses. Present chapter highlights the mechanisms involved in plant endophyte interactions and the role of endophytic fungi as biostimulants of plant growth under stress conditions.
... Other works revealed that colonized root cells underwent diverse cytological and metabolic changes, from the modulation of plastid biosynthetic pathways and Krebs cycle to increases in the production of fatty acids, apocarotenoids, amino acids, flavonoids, such as quercetin, acacetin and rhamnetin, isoprenoids, polyketides and polyphenols [45][46][47][48][49][50][51][52]. The modification in the activity of antioxidant enzymes, including superoxide dismutase, both in roots and shoots of different plants, suggested a positive role of AMF in the protection from oxidative damages caused by biotic and abiotic stresses [53][54][55][56][57]. Accordingly, the increased expression of defense genes encoding phenylalanine ammonia-lyase in Oryza sativa and Medicago truncatula roots and chalcone synthase in Medicago truncatula roots well supported this hypothesis [58][59][60]. Several mechanistic studies, aimed at assessing the differential expression of genes encoding for some of the enzymes leading to the production of health-promoting phytochemicals, showed that they were upregulated in mycorrhizal plants, compared with controls [60][61][62][63][64][65]. ...
The concept of food quality, traditionally based on nutritional and sensory properties, has recently acquired an additional meaning, referring to the health-promoting properties of plant products, that are ascribed to plant secondary metabolites called phytochemicals, primarily represented by polyphenolic compounds and glucosinolates. The diversity and content of phytochemicals in plant products are affected by different variables, such as plant genotype, agronomic factors, and arbuscular mycorrhizal fungi (AMF), which establish mycorrhizal symbioses with most crops, including cereals, legumes, vegetables, fruit trees, sunflower, cotton, and sugarcane. AMF and associated bacteria enhance plant growth and health, and affect the production of polyphenols and carotenoids, and the activity of antioxidant enzymes. The production of health-promoting phytochemicals was shown to be differentially modulated by different AMF isolates and bacterial strains, in several food plants, i.e., tomato, lettuce, strawberry, artichoke, maize, grapevine, sunflower. Here, we provide an overview of recent studies concerning the multiple roles played by AMF and associated bacteria in the modulation of the biosynthesis of plant secondary metabolites with health-promoting activity, and discuss the development of designed multifunctional consortia to be used in sustainable agriculture.
... Inoculation with Mycorrhiza improved CAT and POX activities by 29% and 23% respectively at the level of 12 dS/m versus salinized plants. These results were in agreement with (Blilou et al., 2000 andMittova et al., 2004) Abdel latef and Chaoxing (2011) indicated that higher activity of antioxidant enzymes in plants inoculated with AMF in comparison to un-inoculated plants was related to lower accumulation of lipid peroxidation, which indicated the least oxidative damage in the colonized plants. ...
The objective of the research was to study the response of tomato plants inoculation with arbuscular mycorrhizal fungi (AMF) and tolerance to salinity concentrations (0, 3, 6, 9 and 12dS/m) under greenhouse conditions. The results indicated that the salt stress significantly reduced AMF root infection and growth parameters as compared with the control. Inoculation with AMF significantly achieved higher plant height, root length, number and dry weight of leaves, dry weight of roots, dry weight of stem, leaf area, photosynthesis and fruit weight at all salinity levels, when compared with plants without mycorrhiza inoculation. Salinity significantly decreased uptake of minerals (N, P, K,) and K/Na ratio, also increased uptake of Na. Inoculation with AMF caused a significantly enhanced N, P, K and N-content and P-content, and reduced Na concentration compared with non AMF plants grown under saline and non-saline stress. Catalase (CAT) and peroxidase (POX) activities in tomato leaves of mycorrhizal and non-mycorrhizal treatments were enhanced under different salinity concentrations. Both enzymes had risen under salinity conditions in the beginning of treatment. Inoculation with AMF worked to improve these enzyme activities in different salt levels. In addition, inoculation with AMF significantly increased proline content of tomato plants in comparison with un-inoculated plants. Proline production confirmed a positive line correlation with salinity concentration. In conclusion, inoculation with AMF could alleviate the growth restriction caused by salinity conditions, and play a very important role in promoting tomato plant growth under salt stress.
... The AMF treatments mainly intensified the effect of low temperature at 5°C, suggesting that an enhanced phenolics metabolism by AMF inoculation might also play a crucial role in the AMF-mediated alleviation of cold stress in our eggplants, as observed in cucumber by Chen et al. (2013). Enhanced activity of PAL and accumulation of phenolics are features of many biotic interactions in plants (Blilou et al., 2000;Derksen et al., 2013), including AMF colonization (Hajiboland et al., 2019). The phenylpropanoid pathway upregulation is either a specific host-AMF signaling or a reflection of plant defense strategy (García-Garrido and Ocampo, 2002). ...
Eggplant (Solanum melongena L.) is a thermophilic species susceptible to cold stress. The potential of arbuscular mycorrhizal fungi (AMF) for the amelioration of cold stress in this species has not been investigated so far. This study was conducted to examine some of the physiological functions through which the AMF colonization may improve cold stress tolerance in this species. Plants were inoculated with four AMF species (Funneliformis mosseae, Claroideoglomus etunicatum, Rhizophagus irregularis, and Diversispora versiformis), grown for three weeks under growth chamber conditions, and then treated with three different temperatures (25 °C, 15 °C, and 5 °C) for one week. Results showed that despite the reduction in root colonization, AMF were able to alleviate cold stress in the eggplants by improving photochemical reactions, activating antioxidant defense systems, accumulating protecting molecules, and reducing membrane damages. Cold stress mitigation through AMF was mediated by H2O2 as a priming molecule accumulated upon mycorrhization prior to cold stress. A comparison of four AMF species showed that D. versiformis was less effective than the other three fungal species in alleviating cold stress due to the inability to accumulate the protecting molecules, particularly proline and free phenolics. Our results revealed that AMF inoculation with suitable fungal species is an effective strategy for alleviating cold stress in eggplants.
... Besides having a role in enhancing plants' growth and suppressing plant diseases through processes such as the production of growth-promoting compounds (Duffy et al. 2004), microbes are also reported to be able to reprogram molecular signaling inside rice plants (Pandey et al. 2016). For example, the expression of a lipid transfer protein gene is regulated in rice roots in response to their colonization by the mycorrhizal fungus Glomus mosseae (Blilou et al. 2000). Transcription levels were increased when the fungus formed appressoria to help it penetrate the root's epidermis, and these levels decreased with the onset of intercellular colonization of the root's cortex. ...
The system of rice intensification (SRI) is an agroecological approach to rice cultivation that seeks to create optimal conditions for healthy plant growth by minimizing inter-plant competition, transplanting widely spaced young single seedlings, and optimizing favorable soil conditions with organic amendments, increased soil aeration by weeding, and controlled water management. These practices improve rice plant growth with yields up to three times more than with conventional cultivation methods, and increase crop resilience under biotic and abiotic stresses. This review discusses the roles of beneficial microbes in improving rice plant growth, yield, and resilience when SRI practices are used, and how these modifications in plant, soil, water, and nutrient management affect the populations and diversity of soil microorganisms. Mechanisms whereby symbiotic microbes support rice plants’ growth and performance are also discussed.
... Microbe-mediated plant growth is a multigenic process that is likely to be specific to the participating microbes and plant species (Bharti et al. 2016). An earlier study that showed a lipid-transfer protein gene was up-regulated in rice roots in response to colonization by Glomus mosseae (Blilou et al. 2000). In another study, some genes in P. stutzeri bacteria were switched on during rice root colonization but were switched off when grown on a synthetic medium (Rediers et al. 2003). ...
The fungal species Trichoderma is reported to have a significant impact on the growth and physiological performance of rice plants. However, the molecular mechanisms that induce these effects remain unspecified. Using next-generation sequencing technology, this study compared the differential expression of genes in rice seedlings that had been inoculated with Trichoderma asperellum SL2 with the gene expression in seedlings that had no such inoculation. The study showed that many genes related to plant growth enhancement and physiological functioning are differentially expressed in seedlings which have been symbiotically colonized by T. asperellum SL2. In these seedlings, specific genes related to photosynthesis, RNA activity, stomatal activity, and root development were found to be up-regulated as others were down-regulated. Although the exact causal mechanisms at the molecular level remain to be identified, the presence of Trichoderma versus its absence was associated with almost ten times more significant up-regulations than down-regulations for specific genes that have been identified from previous genomic mapping. Such analysis at the molecular level can help to explain observed phenotypic effects at the organismic level, and it begins to illuminate the observed beneficial relationships expressed phenotypically between crop plants and certain symbiotic microbes.
... Furthermore, SA has long been known to play a major role in reducing plant stress, increasing the antioxidant activity (Shi et al., 2009) and promoting activation and modulation of plant defense responses, especially in interaction with biotrophic pathogens (Beckers and Spoel, 2006;Lu, 2009). Exogenous applications of SA was shown to reduce mycorrhizal development, at least during the first weeks (Blilou et al., 2000;Costa et al., 2000;Özgönen et al., 2001;de Román et al., 2011), but neutral responses were also observed (Ludwig-Müller et al., 2002;Ansari et al., 2016). AM colonization can also increase following soaking seeds with SA (Garg and Bharti, 2018). ...
Arbuscular mycorrhizal (AM) fungi establish probably one of the oldest mutualistic relationships with the roots of most plants on earth. The wide distribution of these fungi in almost all soil ecotypes and the broad range of host plant species demonstrate their strong plasticity to cope with various environmental conditions. AM fungi elaborate fine-tuned molecular interactions with plants that determine their spread within root cortical tissues. Interactions with endomycorrhizal fungi can bring various benefits to plants, such as improved nutritional status, higher photosynthesis, protection against biotic and abiotic stresses based on regulation of many physiological processes which participate in promoting plant performances. In turn, host plants provide a specific habitat as physical support and a favorable metabolic frame, allowing uptake and assimilation of compounds required for the life cycle completion of these obligate biotrophic fungi. The search for formal and direct evidences of fungal energetic needs raised strong motivated projects since decades, but the impossibility to produce AM fungi under axenic conditions remains a deep enigma and still feeds numerous debates. Here, we review and discuss the initial favorable and non-favorable metabolic plant context that may fate the mycorrhizal behavior, with a focus on hormone interplays and their links with mitochondrial respiration, carbon partitioning and plant defense system, structured according to the action of phosphorus as a main limiting factor for mycorrhizal symbiosis. Then, we provide with models and discuss their significances to propose metabolic targets that could allow to develop innovations for the production and application of AM fungal inocula.
... Blilou et al., 2000Silva et al., 2006Coquoz et al., 1998Way et al., 2002Shadle et al., 2003 ١۴۴ Journal of Agricultural Biotechnology; Printing ISSN: 2228-6705, Electronic ISSN: 2228-6500 Pst Figure 5-CAT pattern of gene expression in control plants, treated with salicylic acid and jasmonic acid in various times after infection with Pst. ١۴۵ Journal of Agricultural Biotechnology; Printing ISSN: 2228-6705, Electronic ISSN: 2228-6500Yang et al., 2013Mittler et al., 2004Baker et al., 1997 ...
Tobacco as a model plant (owing to certain features) is extensively used in molecular research
with the aims to understand the fundamental plant and pathogen interactions. Fire blight bacterial
disease of tobacco (Pseudomonas syringae pv. tabaci (Pst)) causes considerable damage to tobacco
worldwide. Induction of genes associated with virulence that play a role in resistance to diseases
can be effective in reducing the severity of disease. The evidence suggests that plant hormones are
effective in gene expression in plants and increase the production of secondary metabolites. In
addition, they stimulate the immune system of plant through the activation of transcription of genes
linked with plant defense mechanisms that regulate the induced resistance. In this study, the
expression of PR1, PR5, Pal, Catalase and WRKY12 in tobacco plants treated with salicylic acid
at a concentration of 3 mM and tobacco plant treated with jasmonic acid at a concentration of 0.5
mM and also control plant in times 0, 12, 24, 48 and 72 after injection of Pseudomonas syrigae pv.
tabaci was investigated by Quantitative Real-time PCR (QRT-PCR) technique. The results showed
that jasmonic acid and particularly salicylic acid treatments caused significant changes in the
expression of these genes after bacterial injection.
key words: Fire blight, Salicylic acid, Jasmonic acid, QRT-PCR, Resistance genes.
*
... In one of these, it was reported that LTPs lead to fungal cell death by inserting themselves into fungal cell membranes and forming a pore which causes efflux of intracellular ions (Selitrennikoff 2001). Besides, in rice, LTPs inhibited the germination of Pyricularia oryzae spores (Ge et al. 2003) and affected the fungal appressoria formation and the penetration of Glomus mosseae (Blilou et al. 2000); in wheat, LTP1 expression was increased in the first 12 h following inoculation and reduced the penetration efficiency of Blumeria graminis f. sp. tritici in a susceptible cultivar by approximately 28.3 % (Li et al. 2006). ...
Over the last decade, comparative molecular
profiling studies between compatible and incompatible
plant-pathogen interactions have shown that susceptible
response of the host to a pathogen requires factors that
promote disease development. In this study, we examined
proteome profiles during a compatible interaction
between wheat and stripe rust. A 2D-LC system
(ProteomeLab PF2D) was used for protein separation
and to compare the proteome from infected and control
samples. More than 700 protein peaks at each time point
were compared between pathogen- and mockinoculated
samples. Selected proteins, with significant
differences in abundance were identified by nanoLCESI-
MS/MS and generated spectra were searched
against the wheat protein databases from UniProt, and
NCBI and the Puccinia database from The Broad Institute.
In total, the identified proteins comprised of 62 %
wheat and 38 % Pst proteins. All identified proteins
were searched by bioinformatics-based algorithms to
detect their subcellular localization and signal peptide
motifs which have the potential to catch the candidate
effector proteins. The wheat proteins were classified
based on their function. Although a compatible interaction,
many wheat proteins, such as antioxidants, PRs
and cold-responsive proteins, are implicated in defense
and stress tolerance. On the pathogen side, 64 proteins
were identified, and included some important pathogenicity
proteins that can play role in pathogen virulence
and suppress the host defense. In addition, we discovered
that nine proteins have a signal sequence and three
of the hypothetical fungal proteins, PGTG_11681T0,
PGTG_07231T0 and CBH50687.1, have been tentatively
identified as candidate effectors.
... Both sodium silicate and SiNP increased cell wall thickness (Table 3), which included an increased lignification (Fig. 1) of the walls and a slight decrease in internal cell area (Table 3). One reason is an increased activity of phenylalanine ammonia-lyase (PAL), which catalyzes the deamination of phenylalanine to cinnamic acid, a precursor for phenolic compounds including lignin (Blilou et al., 2000). The lignification process was mostly evident in the roots of higher Si and SiNP treatments; also, epidermis and cells of primary cortex adjacent to the epidermis were lignified more in the lower treatments (not shown). ...
Silicon (Si) fertilization improves crop cultivation and is commonly added in the form of soluble silicates. However, most natural plant-available Si originates from plant formed amorphous SiO2 particles, phytoliths, similar to SiO2-nanoparticles (SiNP). In this work we, therefore, compared the effect by sodium silicate and that of SiNP on Si accumulation, activity of antioxidative stress enzymes catalase, peroxidase, superoxide dismutase, lignification of xylem cell walls and activity of phenylalanine ammonia-lyase (PAL) as well as expression of genes for the putative silicon transporter (PST), defensive (Tfgd 1) and phosphoenolpyruvate carboxykinase (PEPCK) and protein in fenugreek (Trigonella foenum-graecum L.) grown in hydroponics. The results showed that Si was taken up from both silicate and SiNP treatments and increasing sodium silicate addition increased the translocation of Si to the shoot, while this was not shown with increasing SiNP addition. The silicon transporter PST was upregulated at a greater level when sodium silicate was added compared with SiNP addition. There were no differences in effects between sodium silicate and SiNP treatments on the other parameters measured. Both treatments increased the uptake and accumulation of Si, xylem cell wall lignification, cell wall thickness, PAL activity and protein concentration in seedlings, while there was no effect on antioxidative enzyme activity. Tfgd 1 expression was strongly downregulated in leaves at Si addition. The similarity in effects by silicate and SiNP would be due to that SiNP releases silicate, which may be taken up, shown by a decrease in SiNP particle size with time in the medium.
Arbuscular mycorrhizal fungi (AMF) or arbuscular mycorrhizae (AM) that invade the plant roots or reside in the rhizosphere are considered to be advantageous for plant’s development. AM helps the host plants by making favourable alterations in the rhizospheric soil properties and providing vital mineral nutrients, particularly phosphorus. As symbionts with terrestrial plant roots, arbuscular mycorrhizae (AM) are included under the phylum Glomeromycota. The rhizosphere is the place where AM–plant association begins, and it involves a sequence of chemical induction that is released by both the fungus and the plant. Plants commence communication with AM by secretion of chemical induction into the root zone area of plant, in response to deficiency of nutrients like phosphorus and nitrogen, because AM’s major role in the AM–plant association is to give important nutrients. Most AM spores do not necessarily require the chemical cues to germinate. AM spores were thought to be gone through many stages of germination prior to the discovery of chemical signals from a possible host. The fungus actually looks for plant exudates and then branches out in the direction of the exudates it finds.
Plants have many mechanisms of tolerance to avoid the harmful consequences of various environmental stresses. One of the most crucial tools is the antioxidant system that involves in tolerance mechanism. Osmolyte formation is aided by AM and also supports the ions’ preferential absorption. Moreover, phosphorus nutrition of host plants is not only boosted by AM rather its development and tolerance potentiality towards drought stress and diseases are also improved. The possibility of regulation of plant growth by using AM has been the subject to numerous research studies.
AM can play vital roles in promoting agricultural sustainability, including acting as root symbiont, biofertilizers, enhancing plant water and nutrient absorption, sequestering carbon, making micronutrients more readily available to plants, and improving the surface absorption capacity of host roots. In view of the above, this chapter aims to depict the current state of AM research and its physiology of symbiosis, with a particular focus on AM-induced alterations in plant’s antioxidant and osmolyte metabolisms that support significant adaptations in plants under adverse conditions.
The increasing demand for medicinal plants has emphasized the importance of the development of effective methods
for enhancing the cultivation of these plants. The association of arbuscular mycorrhizal (AM) fungi with medicinal
plants has been found to alter the level of secondary metabolites by affecting the plant metabolism. Lemon balm
(Melissa officinalis L.), is an important medicinal plant which belongs to Lamiaceae family that has been used since the
Middle Ages for various medical purposes. In this study, the effects of Glomus mosseae and Glomus intraradices
symbiosis on growth, the content of some phenolic compounds and the activities of some enzymes responsible for
polyphenols synthesis were investigated in lemon balm. Seeds were sown in a mixture of soil and fungal inoculum.
After five months of growth under controlled condition, growth parameters, the contents of total phenols, flavonoids,
phenolic acids and anthocyanins, the concentrations of rosmarinic acid, salvianolic acid B and caffeic acid and activities
of phenylalanine ammonia lyase and tyrosine aminotransferase were investigated in the control and the AM plants.
According to the results, the symbiosis of lemon balm with selective AM species was successful. The highest
percentage of colonization and the improvement of growth parameters were observed in the plants inoculated with G.
mosseae. Symbiotic plants showed more increased levels of polyphenols and enzymes activities compared to the
control. The study revealed that colonization of plants with AM species not only improved growth, but also increased
the content of polyphenols which is closely linked to the enzymes activities responsible for synthesis of these
compounds. These results confirmed the importance of the mycorrhizal symbiosis in enhancing the nutritional and
medicinal values of the plant.
Bread Wheat is one of the most important crops which has main position in nutrition of the world's population. Powdery mildew, caused by the biotrophic pathogen Blumeria graminis f.sp tritici (Bgt), known as a destructive disease of wheat worldwide. There are several methods to control the disease, but use of
inducers able to induce a systemic resistance in plants are very important. As of Piriformospora indica endomycorrhiza fungi and salicylic acid after symbioted with roots and inoculated on plants, respectively, with inducting systemic resistance can play a pivotal role in inducting resistance of plant to pathogens. Plants in response to biological agents produce numerous compounds such as reactive oxygen species,
phytoalexins and a group of proteins called pathogenesis related (PR) proteins. In order to examinate the
expression rate of PR1, PR2, PR3, PR5, PRX, PAL, NPR1, MLO and BI-1 genes using Real Time PCR
technique in response to Bgt and also change pattern of peroxidase, catalase and ascorbate peroxidase
enzymes, 40 Iranian commercial wheat genotypes were screened using Bgt in seedling stage. On the basis of
colonies number formed on samples, cv. Flat was selected as susceptible lines, and cv. Tajan and cv.
Gascojen were selecteted as as spring and winter resistance genotypes, respectively. For testing the ability of
fungus P. indica and SA for inducing resistance in wheat against Bgt fungus, cv. Falat treated seperately and
then exposed to Bgt fungi together with control plants. Similarly, to compare the pattern of genes
expression, cv. Falat together with resistant cultivars were exposed to fungus Bgt. The expression rate of
target genes was carried out at 5 time courses and in 3 independent replicates and then genes expression rate
were normalized in comparing with their relative internal reference Actin gene. Results indicated that in both
groups of treated and control plants, levels were increased after infection for all genes excepts MLO and BI-
1. Maximum expression level of genes were observed at 24 hours after infection. This process was observed
slowly in control plants but caused early and faster induction of plant defense genes in treated plants at early
hours after infection. At 48 hours after inoculatin, transcript levels of induced genes started to dampen in
both groups of experimental plants, indicating effective suppression of defense-associated genes upon
haustorium development. Also, comparing the expression patterns of genes in susceptible and resistant
cultivars showed that the expression of these genes in induced resistant varieties were much faster than the
Falat susceptible cultivar. In addition, the results of this study showed that the antioxidant activities of the
treated plants and resistant varieties are less than of the susceptible cultivar. Therefore, this phenomenon can
promoted the idea that these plants with reduced enzyme activities inducting the rapid cell death that is
combated with the pathogen. While symbiant plants except overexpression of peroxidase enzyme, were not
showed significantly different for other enzyme activitiesy than control plants. Therefore, the symbiotic
fungi seems can not be effective for inducing resistance via enzymatic pathway. Overall, results indicated
that Tajan and Gascojen cultivars with overexpression of resistance genes and antioxidant enzymes have
high potential for improving resistance to powdery mildew. Both of P. indica and SA inducers are able to
induce resistance in susceptible cultivar through overexpression of resistance genes and reducing number of
colonies grown on Bgt fungus p
Book Description:
Arbuscular mycorrhizal fungi (AMF) are considered enormously important in contemporary agriculture and horticulture due to their important role in nutrient, biotic and abiotic stress management apart from enhancing plant health and soil fertility, etc. AMF is one of the important fungi for soil aggregation, which helps in drought management. Hence this proposal brings out an exclusive text on AMF for sustainable rice production. This book will provide a comprehensive up-to-date knowledge on AMF in rice cultivation. It provides knowledge about AM fungi for sustainable rice production in different ecologies without damaging environment. Salient Features: 1. Covers all the aspects of AMF in rice cultivation from diversity to applications 2. Documents AMF diversity based on metagenomic approach in rice ecosystem 3. Explains the importance of AMF in soil aggregation, which helps in drought management 4. Provides new unravelling knowledge about AM fungi for sustainable rice production in different ecologies without damaging environment 5. Discusses AMF role in induction of resistance in rice plants against some pests.
Table of Contents:
1. Mycorrhizal Fungi in the Rice Ecosystem by Debashree Dalai and Muktipada Panda. 2. Metagenomics to Explore Mycorrhizal Diversity in Rice Ecosystem by Shokufeh Moradi, Bahman Khoshru and Debasis Mitra. 3. Arbuscular Mycorrhizal Fungi: for Nutrient Management in Rice by Anuprita Ray and Shuvendu Shekhar Mohapatra. 4. Arbuscular Mycorrhizal Fungi: A Sustainable Approach for Enhancing Phosphorous and Nitrogen Use Efficiency in Rice Cultivation by Wiem Alloun and Debasis Mitra. 5. Arbuscular Mycorrhizal Fungi and its Role in Plant Growth Promotion in Rice by Ankita Priyadarshini, Suchismita Behera, Debasis Mitra, Ansuman Senapati, Swagat Shubhadarshi, Sucharita Satapathy, Subhadra Pattanayak and Periyasamy Panneerselvam. 6. Arbuscular Mycorrhizal Fungi and Strigolactone: Role, Application and Effects of Synthetic Strigolactone in Plant Growth Promotion by Partha Chandra Mondal, Shreosi Biswas, Puranjoy Sar and Biswajit Pramanik. 7. The Beneficial Role of Arbuscular Mycorrhizal Fungi and Their Associated Bacteria for Plant Growth Promotion and Nutrient Management in Rice Cultivation by Bahman Khoshru and Debasis Mitra. 8. An Insight of Physiological and Molecular Mechanisms of Arbuscular Mycorrhizal – Rice Symbiosis in Stress Alleviation by Chaithra Manju, Amit Kumar Dutta, Mahwish Firdous and Debasis Mitra. 9. Arbuscular Mycorrhiza and its Role in Rice Production Under Drought Stress by Biswajit Pramanik, Puranjoy Sar, Shreosi Biswas and Partha Chandra Mondal. 10. Arbuscular Mycorrhiza and its Role in Rice Production Under Salinity Stress by Shampa Purkaystha, Biswajit Pramanik and Anamika Das. 11. Role of Arbuscular Mycorrhizal Fungi in the Alleviation of Heavymetal Stress on Rice by E. Janeeshma, Joy M. Joel, A.M. Shackira, Riya Johnson and Thomas T. T. Dhanya. 12. Arbuscular Mycorrhizal Fungi Association and its Activation of Defense Response to Plant Protection by Khushneet Kaur, Kritika Gupta and Shivangi Singh. 13. Management of Rice Phytopathogens Through Arbuscular Mycorrhizal Fungi by Shraddha Bhaskar Sawant, Ankita Behura and S. R. Prabhukarthikeyan. 14. Role of Arbuscular Mycorrhizal Fungi in Rice Insect and Nematode Management by Guru-Pirasanna-Pandi G., Swagatika Sahoo and Sampriti Mohanty. 15. Arbuscular Mycorrhizal Fungi Associated Bacteria and Their Role in Plant Protection in Rice Cultivation by Mamun Mandal, Abhijit Sarkar. 16. Arbuscular Mycorrhizal Fungi and its Association for Bioremediataion in Rice Cultivation by Shuvendu Shekhar Mohapatra, Anuprita Ray, Sonali Panda, Sucharita Satapathy and Nutan Moharana. 17. AM Fungi Interactions in Rice Seedling Production by Nurudeen Olatunbosun Adeyemi, Oni Olanrewaju Emmanuel and Debasis Mitra. 18. AM Fungi Role in Soil Health Management by Priyanka Adhikari, Kuldeep Joshi and Pooja Thathola. 19. OMICS Sciences for Deciphering Plant – Mycorrhizal Symbiosis by Aishwarya Purohit, Debashish Ghosh, Rajesh Kumar and Amar Jyoti Das. 20. AM Fungi: Mass Production, Quality Control and Application by Sucharita Satapathy, Shuvendu Shekhar Mohapatra, Puranjoy Sar, Ankita Priyadarshini, Debasis Mitra and Subhadra Pattanayak. 21. AM Fungi Production Upscaling, Government Regulations, Marketing and Commercialization by Wiem Alloun, Somya Sinha and Debasis Mitra. 22. Rice Seed Priming with AMF and AMF-Associated Bacteria for Crop Enhancement by R. Djebaili, B. Farda, G. Capoani, G. Pagnani and M. Pellegrini. 23. Arbuscular Mycorrhizal Fungi in the Control of Fungal Diseases in Rice by Jorge Poveda. 24. Arbuscular Mycorrhizal Fungi Role in Bioremediation in Rice in the Context of Climate Change by Sarah González Henao and Thaura Ghneim-Herrera. 25. Rice - Mycorrhizal Interaction: Enhances the Biocontrol Efficiency Through Integrated Approaches by Wiem Alloun, Izdihar Ferhat, Hadjer Kecies, Aya Rehouma and Abdelkader Mahrouk.
Plant non-specific lipid transfer proteins (nsLTPs) are small, basic, and cysteine-rich proteins found abundantly in higher plants. Apart from main processes like the membrane stabilization, cell wall organization, cuticle synthesis, plant growth and development, and signal transduction, nsLTPs have an active role in abiotic and biotic stress tolerance. Their structure consists of a conserved motif with eight-cysteine residues, stabilized by four disulfide bonds that make an inner hydrophobic cavity for ligand binding. This structural conformation renders stability and means for the transport of a variety of hydrophobic molecules. The nsLTPs possess significant inhibitory activity against the pathogenic microorganisms and thus make a part of the immunity in the plant’s defense system. Due to their small size, LTPs penetrate the fungal and bacterial membrane, creating pores that cause the efflux of the intracellular ions and eventually the cell death. Several genes encoding LTPs with antimicrobial potential have been integrated and overexpressed in plants either alone or in combination with other peptides for improved disease resistance. This review summarizes nsLTPs, their structural characteristics, and expression in various plant species to combat phytopathogens with enhanced disease resistance.
Arbuscular mycorrhiza (AM) is a symbiont formed by the interaction and mutual recognition of soil-born AM fungi and the roots of most vascular plants in the long-term evolution. The development and function of AM, limited by environmental conditions, especially the soil nutrient level, drought, and salinity, depend on the precise “molecular dialogue” between AM fungi and host plants. Phytohormones are low-molecular-weight organics with low concentration and act as crucial signaling molecules in the regulation of AM symbiosis. There are mainly nine phytohormones participating in regulating AM development with different effects. Strigolactones (SLs) act at the first symbiotic recognition between AM fungi and host plants. At the early stage, abscisic acid (ABA) and brassinosteroid (BR) promote the fungal invasion, whereas salicylic acid (SA) and ethylene (ET) inhibit the fungal invasion. Auxin (Aux), ABA, and BR promote the subsequent arbuscule formation, whereas ET and gibberellin (GA) suppress the arbuscule formation. Jasmonic acid (JA) may have both positive and negative regulating effects on fungal invasion and arbuscule formation. However, the role of cytokinin (CTK) remains unclear in AM development. In addition, the signaling crosstalk among phytohormones normally determines AM development. This review summarized the characteristics of different phytohormones and their associated signaling crosstalk (synergistic or antagonistic) in regulating AM development, and the possible regulation mechanisms of different phytohormone signals involved in AM development under stress conditions. The profound research and systematical illustration of the physiological/molecular mechanisms of phytohormones in regulating the symbiotic relationships between AM fungi and host plants, will help the study on symbiology and the application of mycorrhizal technology.
Peppermint is an important medicinal plant, particularly regarding its high essential oil (EO) content. The present study assesses the effects of two Arbuscular mycorrhiza fungi (AMFs) and three concentrations of Titanium dioxide nanoparticles (TiO2 NPs) (i.e., 100, 150, and 200 mg L−1) on growth characteristics, EO constituents, phenolic content and anti-oxidative enzymatic activities of peppermint. Applying a mixed treatment of Glomus intraradices and TiO2 NPs (150 mg L-1) enhanced peppermint's shoot-fresh and dry weight by 69% and 158%, respectively, compared with controls. Also, membrane stability index (MSI) and leaf relative water content (RWC) exhibited a maximum enrichment of 69.85% and 39%, respectively, over control. Some other plant physiological characteristics were also positively affected by applying either the single or combined treatment of G. intradices and TiO2 NPs (150 mg L−1). In this regard, total phenolic content increased by 300%, DPPH radical scavenging ability by 164%, catalase by 103%, and ascorbate peroxidase activities by 124% in mixed treatment of Glomus intraradices and TiO2 NPs (150 mg L−1). Moreover, AMF symbiosis and the implementation of TiO2 NPs intervention augmented the amount of peppermint EO compounds such as menthol, menthyl acetate, and 1, 8 cineole. The highest amount of menthol production (52.04%) was obtained by adding a mixture of G. intraradices and TiO2 NPs (150 mg L−1), which had more positive effects on the other studied characteristics. Overall, AMF symbiosis and TiO2 NPs application seem suitable for promoting plant growth, improving antioxidant activity, and incrementing major components of EOs in medicinal plants.
Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) have positive impacts on growth and production of plants under saline condition. However, their interactive effects on plant behavior under salt stress remained unclear. To address this, a glasshouse experiment was conducted to elucidate the effect of the single and combined (co-inoculation) application of Glomus mosseae (Gm) AMF and Streptomyces rimosus (Sr) PGPR on salt tolerance of Sultana grapevine (Vitis vinifera L.). Based on results, the combined inoculation with Gm AMF and Sr PGPR markedly improved shoot and root morphometric traits and also soluble carbohydrate, soluble proteins, proline content compared to those vines inoculated with these symbionts alone or uninoculated vines under saline condition. The highest main root length was related to inoculated vines with Sr PGPR, which was 18.5% higher than uninoculated control plants under saline condition. Under saline condition, co-inoculation with Gm AMF and Sr PGPR decreased leaf necrotic, leaf ion leakage and malondialdehyde content by 31%, 43% and 38% but increased SPAD index, relative water content, catalase and guaiacol peroxidase activity by 45%, 26%, 30% and 53% compared with control uninoculated plant. Among salt stressed plants, the single inoculated vines with Gm AMF showed the highest total phenol and flavonoid content compared to control plants. In vines grown under saline condition, the highest content of leaf P, Mg, Fe, Zn and Mn were related to Gm plus Sr -inoculated vines. Leaf NO-3 and K of all inoculated vines did not showed statistically significant difference with each other's. Under saline condition, root NO3, K, Mg, Fe, Zn and Mn did not showed significant difference among inoculated plants but differed significantly with control vines. Therefore, combined application of Gm AMF and Sr PGPR assisted host plants to uptake higher nutrients during salt stress; confer salt tolerance to vines by increase in osmoregulants, phenolic compounds and antioxidant enzymes activities in their tissues.
Arbuscular mycorrhiza (AM) is a mutualistic symbiosis formed between most land plants and Glomeromycotina fungi. During symbiosis, plants provide organic carbon to fungi in exchange for mineral nutrients. Previous legume studies showed that the required for arbuscular mycorrhization2 (RAM2) gene is necessary for transferring lipids from plants to AM fungi (AMF) and is also likely to play a “signaling” role at the root surface. To further explore RAM2 functions in other plant lineages, in this study, two rice (Oryza sativa) genes, OsRAM2 and OsRAM2L, were identified as orthologs of legume RAM2. Examining their expression patterns during symbiosis revealed that only OsRAM2 was strongly upregulated upon AMF inoculation. CRISPR/Cas9 mutagenesis was then performed to obtain three Osram2 mutant lines (-1, -2, and -3). After inoculation by AMF Rhizophagus irregularis or Funneliformis mosseae, all of the mutant lines showed extremely low colonization rates and the rarely observed arbuscules were all defective, thus supporting a conserved “nutritional” role of RAM2 between monocot and dicot lineages. As for the signaling role, although the hyphopodia numbers formed by both AMF on Osram2 mutants were indeed reduced, their morphology showed no abnormality, with fungal hyphae invading roots successfully. Promoter activities further indicated that OsRAM2 was not expressed in epidermal cells below hyphopodia or outer cortical cells enclosing fungal hyphae but instead expressed exclusively in cortical cells containing arbuscules. Therefore, this suggested an indirect role of RAM2 rather than a direct involvement in determining the symbiosis signals at the root surface.
[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022.
Phenylalanine ammonia-lyase (PAL) is a rate-limiting enzyme of phenylpropanoid biosynthesis in plants that synthesise many ubiquitous key compounds, including phenolic acids, flavonoids, lignins, and stilbenes. The first draft of the full grape genome assembly was released, but systematic analysis of the PAL family has not been completed in detail. In this study, 15 PALs were identified in the grape genome. Grape PALs are distributed on 6 chromosomes, and 9 PALs are distributed on chromosome 16, in which most of the 2 downstream genes, including chalcone synthase (CHS) and stilbene synthase (STS). Promoter analysis revealed that there were many cis-acting elements in the promoter regions to respond to light, phytohormone, and stress. According to transcriptome-data analysis, VvPALs have extensive expression patterns in various tissues and developmental stages in response to various stresses. Dynamic expression patterns of PAL1/2/3/5 were observed in different developmental stages of 4 grape varieties on the basis of qRT-PCR analysis, and suggested that PALs are involved in a complex mechanism to modulate in anthocyanin biosynthesis. Comprehensive analysis of PALs offers a basis for further understanding the physiological functions of PALs during grape development and their potential role to respond the various stimuli.
To protect the plant from various diseases and pests, modern agriculture depends on mainly chemical pesticides or fungicides. But due to indiscriminate use of these chemicals and rise of resistance to chemicals in pests and pathogens, scientists shifted the attention from chemical pesticides to alternative approaches for crop protection. To replace synthetic chemical pesticides, eco-friendly sustainable agrisystem is urgent and scientists paid much attention to fungi as they are potent biocontrol agents (BCA) for plant protection from several pathogens. Several fungi such as Trichoderma, Penicillium, Fusarium, Aspergillus, mycorrhizal associations, yeasts, etc. have been recognized as potent fungal biocontrol agents (FBCAs), and simultaneously they already have been applied in agricultural fields for protecting crops or plants. Mechanisms of direct or indirect plant pathogen suppressing or killing and induction or increasing of plant immunity or resistance have been studied. Cell signaling such as salicylic acid (SA), jasmonic acid (JA), ethylene pathways (ET) MAPK, G protein pathways, and PR (pathogenesis-related) proteins, elicitors, ISR (induced systematic resistance), SAR (systemic acquired resistance), etc. are involved in fungal-induced disease resistance of plants. Cross-talking among different cell signaling pathways are also noted. Transgenic approaches and elicitor approaches by FBCA for crop protection have been also summarized here.
Basil (Ocimum basilicum L.) is a high-value medicinal herb cultivated for economical applications, especially pharmaceutical purposes. There is less information on the effects of arbuscular mycorrhizal (AM) fungi, drought stress, and phosphorus (P) supply on important phenolic compounds like caffeic (CA) and rosmarinic (RA) acids. Therefore, an experiment was performed to examine whether treatments: AM (inoculated with Glomus hoi and non-inoculated (NM) plants; drought stress (60% field capacity (FC)) and well-irrigated (90% FC) and phosphorus supply (0.1, 0.2 and 0.3 g/kg of soil) could influence plant growth and contents of total phenols (TPC), RA, CA and phenylalanine ammonia-lyase (PAL) activity. The experiment was conducted as a factorial oriented by completely random design with three repetitions. Shoots of 8-week-old plants that were subjected to all mentioned treatments were harvested and analyzed. High-performance liquid chromatography (HPLC) was used to quantify RA and CA contents. Results indicated that both P supply and AM inoculation enhanced plant growth, tissue P content, RA and CA production and PAL activity. There was an increase of 1.84, 1.59, and 2.22 times for TPC, RA and CA contents respectively in AM plants compared to NM plants in P2 levels and in drought stress. There was a positive relationship between the phenol content and PAL activity for all the treatments. Consequently, mycorrhizal inoculation and application of an appropriate level of P could serve as an adaptive strategy to enhance productivity and plant synthesis of phenolic compounds under restricted irrigation with health-promoting activities.
Although heeding and leading in the application perspective, we are lagging to address the variegated cross-talks involved in plant-endophyte interactions, the basis for the pertinence of endophytes. Endophytism represents the phenomenon in which a microbe resides asymptomatically within the plant tissues. The competency of the endophytes to penetrate, colonize, and flourish inside the plant premises by exhibiting complex multivariate interactions with the host, makes them unique. An endophyte, besides dealing with the host has to deal with the existing endospheric microbiota to make its colonization successful. However, we are at the beginning to appreciate the involvement of complex crosstalks between a plant and its endophytic microbiome and among the endophytic microbes associated with the plant. In this review, conglomerate cross-talks existing between plants and endophytes to maintain an ecological balance has been emphasized. Endophytic fungi have developed a palette of strategies to make their subsistence asymptomatic within the host. However, it is still a concern of exploration to unravel all the strategies employed by the endophytes, especially at the molecular level to accomplish this complex cross-kingdom association and making an asymptomatic existence inside the host. In recent years, the bioprospection of endophytes has received much attention, however, the differential survival strategies developed by them are poorly understood. This review summarizes currently available knowledge about the mechanisms behind the endophytic fungal colonization emphasizing the strategies employed by them in maintaining endophytism with special reference to quorum sensing and quorum quenching.
The phytohormone jasmonate (JA) modulates various defense and developmental responses of plants, and is implied in the integration of multiple environmental signals. Given its centrality in regulating plant physiology according to external stimuli, JA influences the establishment of interactions between plant roots and beneficial bacteria or fungi. In many cases, moderate JA signaling promotes the onset of mutualism, while massive JA signaling inhibits it. The output also depends on the compatibility between microbe and host plant and on nutritional or environmental cues. Also, JA biosynthesis and perception participate in the systemic regulation of mutualistic interactions and in microbe-induced resistance to biotic and abiotic stress. Here, we review our current knowledge of the role of JA biosynthesis, signaling, and responses during mutualistic root–microbe interactions.
Arbuscular mycorrhizal fungi (AMF) are potentially mutualistic biotrophs of plants and improve water supply and nutrient uptake in host plants. In exchange of this, it takes a part of photosynthate from the host plant to fulfill its metabolic requirements. Despite having its own immune system, plant gets attacked by various pathogens and therefore needs support to overcome such challenges and to become stabilized in such hostile environment. AMF colonization helps the plants either directly or indirectly to face the challenges of biotic and abiotic stresses. Several physiological and biochemical changes occur in the host plant and mycorrhizosphere following colonization of roots by AMF, and AMF colonization also affects interactions of the host plants with a diverse range of both above- and belowground organisms. Protective effects of AMF colonization against pests, pathogens, and stem or root parasitic plants were described in many agriculturally important crop species. These mechanisms not only improve plant nutrition consumption and competition but also play a significant role in plant defense activation. Successful establishment of mycorrhizal species on host leads to regulation of the JA and SA signaling pathways, and it itself explains the range of protection conferred by this symbiosis. Defense activation following colonization by mycorrhizal species is associated with moderate activation of host transcription factors such as MAP kinases. Further, several other defense-related compounds are also accumulated such as PR proteins, β-1,3-glucanases, phytoalexins, and phenolics, and deposition of callose also occurs leading to protection against various pathogens. In the present chapter, we discussed the major defense signaling aspects during plant-pathogen interactions mediated through mycorrhizal colonization in the host plant roots.
Bambusapervariabilis×Dendrocalamopsisgrandis, a fast-growing and easily propagated bamboo species, has been extensively planted in the southern China, resulting in huge ecological benefits. In recent years, it was found that the pathogenic fungus Arthrinium phaeospermum caused the death of a large amount of bamboo. In this study, the transcriptome of B. pervariabilis × D. grandis, induced by inactivated protein AP-toxin from A. phaeospermum was sequenced and analyzed, to reveal the resistance mechanism induced by biotic agents of B. pervariabilis × D. grandis against A. phaeospermum at the gene level. Transcriptome sequencing was performed by Illumina HiSeq 2000 in order to analyze the differentially expressed genes (DEGs) of B. pervariabilis × D. grandis in response to different treatment conditions. In total, 201,875,606 clean reads were obtained, and the percentage of Q30 bases in each sample was more than 94.21%. There were 6398 DEGs in the D-J group (inoculation with a pathogenic spore suspension after three days of AP-toxin induction) compared to the S-J group (inoculation with a pathogenic spore suspension after inoculation of sterile water for three days) with 3297 up-regulated and 3101 down-regulated genes. For the D-S group (inoculation with sterile water after inoculation of AP-toxin for three days), there were 2032 DEGs in comparison to the S-S group (inoculation with sterile water only), with 1035 up-regulated genes and 997 down-regulated genes. These identified genes were mainly involved in lignin and phytoprotein synthesis, tetrapyrrole synthesis, redox reactions, photosynthesis, and other processes. The fluorescence quantitative results showed that 22 pairs of primer amplification products were up-regulated and 7 were down-regulated. The rate of similarity between these results and the sequencing results of the transcription group was 100%, which confirmed the authenticity of the transcriptome sequencing results. Redox proteins, phenylalanine ammonia lyase, and S-adenosine-L-methionine synthetase, among others, were highly expressed; these results may indicate the level of disease resistance of the bamboo. These results provide a foundation for the further exploration of resistance genes and their functions.
Plants being exposed to a variety of pathogenic infections, acquire the natural mechanism of combating the pathogens leading to an increased level of defense. Several pathogenesis-related (PR) proteins are expressed by plants; approximately 17 families have been discovered till now. Most of them confer resistance to fungal pathogens and some of the PR proteins are bactericidal. These PR proteins consist of a short sequence of amino acids thus called antimicrobial peptides (AMPs). These AMPs permeabilize the pathogenic membrane via pore formation leading to cell death. The specific characteristic of these peptides is conserved domain and the disulfide bond pattern. Several types of AMPs such as defensins, thionins, cyclotides, lipid transfer proteins (LTPs) and several others, with a diverse mode of action, have been characterized from different plant species. These AMPs have been playing an important role in the host plant’s defense against the pathogens. In this review we summarized types of AMPs, their structural conformation and mode of action, their expression and co-expression in transgenic plants for conferring elevated resistance against the phytopathogens.
Fusarium oxysporum is an important soilborne destructive plant pathogen that has an effect on several plant species worldwide. The suggested practice for their effective control was the integration of several management practices, but it remains elusive till now. Since it is important to develop disease-resistant and high-yielding crops due to the increase in food demand with minimum utilization of natural resources, it is necessary that the prerequisite employment methodology be of biological origin and that the candidature for the role of biological control agents implies antagonists in various plant–microbe interactions such as arbuscular mycorrhizal fungi and Trichoderma spp. This review proposes a framework that might be helpful in the use of AM fungi and Trichoderma spp. for their effective biocontrol of several plant pathogens and insights into the mechanisms involved. Also, a relationship between arbuscular mycorrhizal fungi or Trichoderma spp. and the host plant is being emphasized upon for improved health and growth for production in present agricultural systems. Therefore, this review focuses on some approaches aimed at the biocontrol of F. oxysporum and biotechnological advancement involved in it for paving insights for future research.
Throughout the world agriculture has need to twofold increase in food production by 2050 in order to meet the burgeoning population with decrease its necessity on factory made fertilizers and plant protection chemicals. This may be attained through exploring multiple options of utilizing beneficial microorganisms and its suitable interaction in agroecosystem of the concerned surroundings. Our agricultural system is a multifaceted system of exchanges between plants and microorganisms. Increasing demand for economically well-matched, surroundings sociable technique in farming that might be able to provide sufficient nutrients for the growing human inhabitants through upgrading of the worth and scale of farming yield with the help of eco-friendly microbes present in nature. In this aspect, microorganisms play a key role. Beneficial effects of microorganisms on herbal progress mainly include uptake of major soil nutrients mainly NPK, etc., advanced growth of young branches and roots, improvement of soil productivity, and lastly proper nitrogen fixations and acquisition of soil nitrogen. Some of the frequently used beneficial microbes in agriculture globally include Bacillus, Azospirillum, Trichoderma, Rhizobia, Mycorrhizae, Pseudomonas, Streptomyces, and many other species. Exploring modern techniques with molecular biology helps to exploit valuable microbes and its products that leads to enhancing farm productivity and improvement of soil quality on sustainable basis.
Heat-acclimation or salicylic acid (SA) treatments were previously shown to induce thermotolerance in mustard (Sinapis alba L.) seedlings from 1.5 to 4 h after treatment. In the present study we investigated changes in endogenous SA and antioxidants in relation to induced thermotolerance. Thirty minutes into a 1-h heat-acclimation treatment glucosylated SA had increased 5.5-fold and then declined during the next 6 h. Increases in free SA were smaller (2-fold) but significant. Changes in antioxidants showed the following similarities after either heat-acclimation or SA treatment. The reduced-to-oxidized ascorbate ratio was 5-fold lower than the controls 1 h after treatment but recovered by 2 h. The glutathione pool became slightly more oxidized from 2 h after treatment. Glutathione reductase activity was more than 50% higher during the first 2 h. Activities of dehydroascorbate reductase and monodehydroascorbate reductase decreased by at least 25% during the first 2 h but were 20% to 60% higher than the control levels after 3 to 6 h. One hour after heat acclimation ascorbate peroxidase activity was increased by 30%. Young leaves appeared to be better protected by antioxidant enzymes following heat acclimation than the cotyledons or stem. Changes in endogenous SA and antioxidants may be involved in heat acclimation.
Mycorrhiza-resistant and non-nodulating pea mutants provide a model system for identifying common genes regulated during the early events in mycorrhiza and nodule establishment. Inoculation of pea roots with Glomus mosseae or Rhizobium leguminosarum can induce overexpression of seven defense-related genes (pI 206, pI 49, pI 176, PR 10, basic A1-chitinase, transcinnamic acid 4-hydroxylase, chalcone isomerase), depending on the plant genotype and the time point of interaction between the plant and the microsymbiont. Expression of the pI 206 gene is closely correlated with appressorium formation by the mycorrhizal fungus on both mutant and wild-type pea roots. The gene is also induced by the pathogen Aphanomyces euteiches. Transcript accumulation was higher in mutant than in wild-type genotypes for five and six of the studied genes during early stages of root interactions with G. mosseae and R. leguminosarum, respectively, and this is discussed in relation to the symbiotic-defective phenotype of Myc-1Nod- pea. The early induction of similar plant defense genes in response to arbuscular mycorrhizal fungi and rhizobia reinforces the hypothesis of common regulatory steps in both root symbioses.
Plant species that are hosts of non-arbuscular mycorrhizas were utilized to investigate the early processes involved in host recognition by arbuscular mycorrhizal fungi. The roots of plant hosts of ecto-, arbutoid and ericoid mycorrhizas, as well as those of non-mycorrhizal species, did not elicit the differential morphogenesis that occurred in the hyphae of Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe when challenged with the roots of its hosts. In the absence of this morphogenetic response, infection structures were not formed, any further step in the recognition process was hindered, and defence reactions did not occur. The ability of arbuscular mycorrhizal fungi to discriminate their specific hosts from alt other plant species through a recognition process is probably determined by chemical signals.
A differentially displayed cDNA clone (MD17) was isolated from tobacco roots (nicotiana tabacum cv. Xanthi-nc) infected with the arbuscular mycorrhizal (AM) fungus Glomus intraradices. The isolated DNA fragment exhibited a reduced level of expression in response to AM establishment and 90% identity with the 3' noncoding sequence of two basic chitinases (EC 3.2.1.14) from N. tabacum. Northern (RNA) blots and Western blots (immunoblots), probed with tobacco basic chitinase gene-specific probe and polyclonal antibodies raised against the chitinase enzyme, yielded hybridization patterns similar to those of MD17. Moreover, the up-regulation of the 32-kDa basic chitinase gene expression in tobacco roots by (1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH) was less effective in mycorrhizal roots than in nonmycorrhizal controls. Suppression of endogenous basic chitinase (32-kDa) expression was also observed in transgenic mycorrhizal plants that constitutively express the 34-kDa basic chitinase A isoform. When plants were grown with an increased phosphate supply, no suppression of the 32-kDa basic chitinase was obtained. These findings indicate that during the colonization and establishment of G. intraradices in tobacco roots, expression of the basic chitinase gene is down-regulated at the mRNA level.
The effect of inoculation with the saprophytic fungi Alternaria alternata or Fusarium equiseti on maize (Zea mays) and lettuce (Lactuca sativa) with or without arbuscular mycorrhizal (AM) colonization by Glomus mosseae was studied in a greenhouse trial. Plant dry weights of non-AM-inoculated maize and lettuce were unaffected by the presence
of A. alternata and F. equiseti. In contrast, A. alternata and F. equiseti decreased plant dry weights and mycorrhization when inoculated to the rhizosphere before G. mosseae. The saprophytic fungi inoculated 2 weeks after G. mosseae did not affect the percentage of root length colonized by the AM endophyte, but did affect its metabolic activity assessed
as succinate dehydrogenase activity. Although F. equiseti inoculated at the same time as G. mosseae did not affect mycorrhization of maize roots, its effect on AM colonization of lettuce roots was similar to that with A. alternata. In the rhizosphere of both plants, the population of saprophytic fungi decreased significantly, but was not affected by the
presence of G. mosseae. Our results suggest that there may have been a direct effect of the saprophytic fungi on the mycorrhizal fungi in the extramatrical
phase of the latter, and when the AM fungus was established in the root the AM fungus was less affected by the saprophytic
fungi.
Nonspecific lipid transfer proteins (LTPs) from plants are characterized by their ability to stimulate phospholipid transfer between membranes in vitro. However, because these proteins are generally located outside of the plasma membrane, it is unlikely that they have a similar role in vivo. As a step toward identifying the function of these proteins, one of several LTP genes from Arabidoposis has been cloned and the expression pattern of the gene has been examined by analysis of the tissue specificity of beta-glucuronidase (GUS) activity in transgenic plants containing LTP promoter-GUS fusions and by in situ mRNA localization. The LTP1 promoter was active early in development in protoderm cells of embryos, vascular tissues, lignified tips of cotyledons, shoot meristem, and stipules. In adult plants, the gene was expressed in epidermal cells of young leaves and the stem. In flowers, expression was observed in the epidermis of all developing influorescence and flower organ primordia, the epidermis of the siliques and the outer ovule wall, the stigma, petal tips, and floral nectaries of mature flowers, and the petal/sepal abscission zone of mature siliques. The presence of GUS activity in guard cells, lateral roots, pollen grains, leaf vascular tissue, and internal cells of stipules and nectaries was not confirmed by in situ hybridizations, supporting previous observations that suggest that the reporter gene is subject to artifactual expression. These results are consistent with a role for the LTP1 gene product in some aspect of secretion or deposition of lipophilic substances in the cell walls of expanding epidermal cells and certain secretory tissues. The LTP1 promoter region contained sequences homologous to putative regulatory elements of genes in the phenylpropanoid biosynthetic pathway, suggesting that the expression of the LTP1 gene may be regulated by the same or similar mechanisms as genes in the phenylpropanoid pathway.
The plant-pathogenic fungus Fusarium oxysporum was successfully transformed with the beta-D-glucuronidase gene from Escherichia coli (gusA) (GUS system) in combination with the gene for nitrate reductase (niaD) as the selectable marker. The frequency of cotransformation, as determined by GUS expression on plates containing medium supplemented with 5-bromo-4-chloro-3-indolyl glucuronide (GUS+), was very high (up to 75%). Southern hybridization analyses of GUS+ transformants revealed that single or multiple copies of the gusA gene were integrated into the genomes. High levels of GUS activity are expressed in some transformants, but activity in F. oxysporum does not appear to be correlated with the copy number of the gusA gene. Since the highest activity was found in a transformant with a single copy, it can be assumed that sequence elements of F. oxysporum integrated upstream of the gene can act as a promoter or enhancer. Expression of the gusA gene was also detected during growth of the fungus in plants, indicating that the GUS system can be used as a sensitive and easy reporter gene assay in F. oxysporum.
Heat-acclimation or salicylic acid (SA) treatments were previously shown to induce thermotolerance in mustard (Sinapis alba L.) seedlings from 1.5 to 4 h after treatment. In the present study we investigated changes in endogenous SA and antioxidants in relation to induced thermotolerance. Thirty minutes into a 1-h heat-acclimation treatment glucosylated SA had increased 5.5-fold and then declined during the next 6 h. Increases in free SA were smaller (2-fold) but significant. Changes in antioxidants showed the following similarities after either heat-acclimation or SA treatment. The reduced-to-oxidized ascorbate ratio was 5-fold lower than the controls 1 h after treatment but recovered by 2 h. The glutathione pool became slightly more oxidized from 2 h after treatment. Glutathione reductase activity was more than 50% higher during the first 2 h. Activities of dehydroascorbate reductase and monodehydroascorbate reductase decreased by at least 25% during the first 2 h but were 20% to 60% higher than the control levels after 3 to 6 h. One hour after heat acclimation ascorbate peroxidase activity was increased by 30%. Young leaves appeared to be better protected by antioxidant enzymes following heat acclimation than the cotyledons or stem. Changes in endogenous SA and antioxidants may be involved in heat acclimation.
Isoflavonoids and steady-state mRNA levels of phenylalanine ammonia-lyase, chalcone isomerase, and isoflavone reductase were followed during a rapid, nearly synchronous infection of alfalfa (Medicago sativa L.) roots by the vesicular arbuscular fungus Glomus intraradices (Schenck & Smith) to test whether previously indicated suppression of the host defense response is regulated by changes in the steady-state mRNA level. Relative amounts of steady-state phenylalanine ammonia-lyase mRNA in the mycorrhizal roots doubled between d 14 and 18 and then immediately declined by 75% to reach and maintain a value lower than the control roots through d 21. Relative levels of chalcone isomerase mRNA in the inoculated roots increased 6-fold between d 14 and 17 and then decreased rapidly to the control level. Isoflavone reductase mRNA was not induced by mycorrhizal colonization. High-performance liquid chromatography, proton-nuclear magnetic resonance, and fast atom bombardment-mass spectrometry analyses showed consistent increases in formononetin levels and transient increases in medicarpin-3-O-glycoside and formononetin conjugates in the inoculated roots when colonization began. As colonization increased, levels of formononetin conjugates declined in mycorrhizal roots below those in uncolonized controls. Medicarpin aglycone, an alfalfa phytoalexin normally associated with pathogenic infections, was not detected at any stage. These findings supply detailed evidence that, during early colonization of plant roots by symbiotic Glomus, defense transcripts are induced and then subsequently suppressed.
Increases in endogenous salicylic acid (SA) levels and induction of several families of pathogenesis-related genes (PR-1 through PR-5) occur during the resistance response of tobacco to tobacco mosaic virus infection. We found that at temperatures that prevent the induction of PR genes and resistance, the increases in SA levels were eliminated. The addition of exogenous SA to infected plants at these temperatures was sufficient to induce the PR genes but not the hypersensitive response. However, when the resistance response was restored by shifting infected plants to permissive temperatures, SA levels increased dramatically and preceded PR-1 gene expression and necrotic lesion formation associated with resistance. SA was also found in a conjugated form whose levels increased in parallel with the free SA levels. The majority of the conjugates appeared to be SA glucosides. The same glucoside was formed when plants were supplied with exogenous SA. These results provide further evidence that endogenous SA signals the induction of certain defense responses and suggests additional complexity in the modulation of this signal.
We studied the effect of constitutive expression of pathogenesis-related proteins (PRs) in tobacco plants on vesicular-arbuscular mycorrhiza. Tobacco lines genetically transformed to express various PRs constitutively under the control of the cauliflower mosaic virus 35S promoter of tobacco were examined. Immunoblot analysis and activity measurements demonstrated high levels of expression of the PRs in the root systems of the plants. Constitutive expression of the following acidic isoforms of tobacco PRs did not affect the time course or the final level of colonization by the vesicular-arbuscular mycorrhizal fungus Glomus mosseae: PR-1a, PR-3 (=PR-Q), PR-Q(prm1), PR-4, and PR-5. Similarly, constitutive expression of an acidic cucumber chitinase, of a basic tobacco chitinase with and without its vacuolar targeting peptide, of a basic (beta)-1,3-glucanase, and of combinations of PR-Q and PR-Q(prm1) or basic chitinase and basic (beta)-1,3-glucanase did not affect colonization by the mycorrhizal fungus. A delay of colonization by G. mosseae was observed in tobacco plants constitutively expressing the acidic isoform of tobacco PR-2, a protein with (beta)-1,3-glucanase activity.
Inoculation of one true leaf of cucumber (Cucumis sativus L.) plants with Pseudomonas syringae pathovar syringae results in the systemic appearance of salicylic acid in the phloem exudates from petioles above, below, and at the site of inoculation. Analysis of phloem exudates from the petioles of leaves 1 and 2 demonstrated that the earliest increases in salicylic acid occurred 8 hours after inoculation of leaf 1 in leaf 1 and 12 hours after inoculation of leaf 1 in leaf 2. Detaching leaf 1 at intervals after inoculation demonstrated that leaf 1 must remain attached for only 4 hours after inoculation to result in the systemic accumulation of salicylic acid. Because the levels of salicylic acid in phloem exudates from leaf 1 did not increase to detectable levels until at least 8 hours after inoculation with P. s. pathovar syringae, the induction of increased levels of salicylic acid throughout the plant are presumably the result of another chemical signal generated from leaf 1 within 4 hours after inoculation. Injection of salicylic acid into tissues at concentrations found in the exudates induced resistance to disease and increased peroxidase activity. Our results support a role for salicylic acid as an endogenous inducer of resistance, but our data also suggest that salicylic acid is not the primary systemic signal of induced resistance in cucumber.
In an effort to identify the signal compound that mediates systemic acquired resistance (SAR), changes in the content of phloem
sap were monitored in cucumber plants inoculated with either tobacco necrosis virus or the fungal pathogen Colletotrichum lagenarium. The concentration of a fluorescent metabolite was observed to increase transiently after inoculation, with a peak reached
before SAR was detected. The compound was purified and identified by gas chromatography-mass spectrometry as salicylic acid,
a known exogenous inducer of resistance. The data suggest that salicylic acid could function as the endogenous signal in the
transmission of SAR in cucumber.
Some cultivars of tobacco are resistant to tobacco mosaic virus (TMV) and synthesize pathogenesis-related (PR) proteins upon infection. In a search for the signal or signals that induce resistance or PR genes, it was found that the endogenous salicylic acid levels in resistant, but not susceptible, cultivars increased at least 20-fold in infected leaves and 5-fold in uninfected leaves after TMV inoculation. Induction of PRl genes paralleled the rise in salicylic acid levels. Since earlier work has demonstrated that treatment with exogenous salicylic acid induces PR genes and resistance, these findings suggest that salicylic acid functions as the natural transduction signal.
A variant of the cauliflower mosaic virus 35S promoter with transcriptional activity approximately tenfold higher than that of the natural promoter was constructed by
tandem duplication of 250 base pairs of upstream sequences. The duplicated region also acted as a strong enhancer of heterologous
promoters, increasing the activity of an adjacent and divergently transcribed transferred DNA gene several hundredfold, and
to a lesser extent, that of another transferred DNA gene from a remote downstream position. This optimized enhancer element
should be very useful for obtaining high levels of expression of foreign genes in transgenic plants.
Inoculation of one true leaf of cucumber (Cucumis sativus L.) plants with Pseudomonas syringae pathovar syringae results in the systemic appearance of salicylic acid in the phloem exudates from petioles above, below, and at the site of inoculation. Analysis of phloem exudates from the petioles of leaves 1 and 2 demonstrated that the earliest increases in salicylic acid occurred 8 hours after inoculation of leaf 1 in leaf 1 and 12 hours after inoculation of leaf 1 in leaf 2. Detaching leaf 1 at intervals after inoculation demonstrated that leaf 1 must remain attached for only 4 hours after inoculation to result in the systemic accumulation of salicylic acid. Because the levels of salicylic acid in phloem exudates from leaf 1 did not increase to detectable levels until at least 8 hours after inoculation with P. s. pathovar syringae, the induction of increased levels of salicylic acid throughout the plant are presumably the result of another chemical signal generated from leaf 1 within 4 hours after inoculation. Injection of salicylic acid into tissues at concentrations found in the exudates induced resistance to disease and increased peroxidase activity. Our results support a role for salicylic acid as an endogenous inducer of resistance, but our data also suggest that salicylic acid is not the primary systemic signal of induced resistance in cucumber.
Arbuscular mycorrhizal (AM) fungi, which date from the Devonian era, must have dealt very early on with problems of plant defence, a tactic which has enabled them to colonize roots of most extant plant taxa. Conversely, plants forming arbuscular mycorrhiza must exert some sort of control over the fungi during symbiotic interactions since mycelial proliferation within roots is confined to the cortical parenchyma tissue. Plants possess a panoply of defence mechanisms which are triggered by microbial attack. Here we review present-day knowledge of defence-related root responses to colonization by AM fungi, and assess their possible implications in the symbiosis. Weak, transient, unco-ordinated or extremely localized activation of inducible defence responses occurs during compatible interactions in AM which differs from that in plant–pathogen interactions. When symbiosis-related plant genes are mutated, typical defence responses are associated with resulting root resistance to arbuscular mycorrhizal fungi whilst, contrastingly, plants constitutively expressing defence genes are unaffected in their symbiotic capacities. The mechanisms by which plants can modulate defence responses during symbiotic interactions and the way in which A1V1 fungi might contend with these are discussed.
S ummary
Mycorrhizal infections formed by different endophytes were examined in 10 crop species grown separately and in pairs in sterilized and unsterile soils. No infection was observed in cabbage, kale, rape or swede (in the supposedly non‐mycorrhizal family Cruciferae) and only traces were seen in sugar beet (supposedly non‐mycorrhizal Chenopodiaceae) when these plants were grown alone. However, slight (< 5 %) infection (cortical mycelium and vesicles, but no arbuscules) developed in some when a mycorrhizal host plant was present and there were many clumps of endophyte mycelium on their root surfaces, usually attached to entry points which had often aborted. Glomus fasciculatus ‘E3’ was a more infective endophyte than Gigaspora margarita. Infection was usually well developed in the host plants barley, lettuce, maize, potato and onion. It was depressed only in a few pairs but no more by the presence of a ‘non‐host’ plant than by a host plant. The results suggest that the barriers to mycorrhizal infection in ‘non‐hosts’ are intrinsic and more probably related to characteristics of the root cortex or epidermis than to any infection‐inhibiting factors that might be released in root exudates.
Pisum sativum L. myc– mutants which fail to form arbuscular mycorrhiza have recently been identified amongst nod– mutants (Duc et al., 1989, Plant Sci. 60, 215–222). The reason for this resistance to symbiotic fungi has been investigated in the case of a locus a mutant (P2) inoculated with Glomus mosseae (Nicol. and Gerd.) Gerd, and Trappe. The fungal symbiont formed viable appressoria in contact with the root surface but its development was stopped at the root epidermis. Abundant material was deposited on the inner face of root cell walls adjacent to the appressoria in the P2 mutant, but not in the wild-genotype parent cultivar (Frisson) forming a symbiotic mycorrhizal infection. Fluorescence, histochemical, cytochemical and immunocytological approaches were used to characterize the paramural deposits in epidermal and hypodermal cells of the mutant. Strong fluorescence under blue light indicated the accumulation of phenolic compounds although polymers like lignin or suberin were not localized. Proteins and glycoproteins were homogeneously distributed within the paramural deposits. In the latter, the periodic acid-thiocarbohydrazide-silver proteinate (PATAg) reaction for 1,4-polysaccharide detection showed a heterogeneous composition with electron-dense points surrounded by non-reactive material, but cytological tests for cellulose and pectin gave weak responses as compared to epidermal and hypodermal walls of the wild genotype. -1,3-Glucans indicative of callose were detected by in-situ immunolocalization in the paramural deposits below appressoria on mutant roots, but not in walls of the wild genotype. Thus, appressorium formation by G. mosseae on roots of the locus a P. sativum mutant elicits wall modifications usually associated with activation of defence responses to pathogens. It is proposed that this locus must be involved in a key event in symbiotic infection processes in P. sativum, and the possible role of complex regulatory interactions between symbiosis and defence genes in endomycorrhiza development is discussed.
Systemic resistance was induced to Pyricularia aryzae in rice by inoculation of the first leaf with the hypersensitive response causing bacterium, Pseudomonas syringae pv. syringae. Lesions caused by Pyricularia oryzae were decreased in number and size by 85% and 50%, respectively, in systemically protected leaves. Increased resistance was associated with the deposition of a dark brown material around sites of Pyricularia oryzae infection. The systemically acquired resistance was not associated with an increase in the activities of phenylalanine ammonia lyase, coniferyl alcohol dehydrogenase, peroxidase, β-1, 3-glucanase or chitinase after the challenge inocculation with Pyricularia oryzae. The levels of these enzymes were elevated by local exposure to Pseudomonas syringae pv. syringae or Pyricularia oryzae, but were not systemically induced. These data suggest that the physiological changes which occur during induced resistance in rice are different from those correlated with induced resistance in tobacco or cucumber.
A number of genera of soil fungi interact with plant roots to establish symbiotic associations whereby phosphate acquired by the fungus is exchanged for fixed carbon from the plant. Recent progress in investigating these associations, designated as mycorrhizae (sing., mycorrhiza), has led to the identification of specific steps in the establishment of the symbiosis in which the fungus and the plant interact in response to various molecular signals. Some of these signals are conserved with those of theRhizobium–legume nitrogen-fixing symbiosis, suggesting that the two plant–microbe interactions share a common signal transduction pathway. Nevertheless, only legume hosts nodulate in response toRhizobium,whereas the vast majority of flowering plants establish mycorrhizal associations. The key questions for the future are: what are the signal molecules produced by mycorrhizal fungi and how are they perceived by the plant?
Genetic resistance to vesicular-arbuscular (VA) mycorrhiza formation has been obtained in spontaneous or chemically induced mutants of two mycorrhiza-forming species (Pisum sativum L. and Vicia faba L.). The eight mutants, termed myc−, are characterized by aborted infections limited to one or two host cells. Expression of the myc− character is associated with that of the nod− character in both legumes, and is likewise under recessive genetic control. Preliminary analysis of the genetic behaviour of the myc− mutants in diallel crosses has shown that at least three genes are involved in VA mycorrhiza infection.
Summary We report here that the pea early nodulin genes PsENOD5 and PsENOD12A are induced during the interaction of pea roots and the endomycorrhizal fungus Gigaspora margarita. Using the pea nodulation mutant Sparkle-R25, which is mutated in SYM8, it is shown that SYM8 is essential for the induction of PsENOD5 and PsENOD12Ain pea roots interacting either with Rhizobium or the endomycorrhizal fungus Gigaspora margarita. Our results suggest that mycorrhizal signals activate a signal transduction cascade sharing at least one common step with the Nod factor-activated signal transduction cascade.
The analysis of SA accumulation in roots of plant symbiotic mutants revealed two independent phenomena associated with the
inability of either the plant or the microsymbiont to form a compatible symbiosis. SA accumulation in roots of the wild type
and symbiosis-resistant P2 (Nod−, Myc−) Pisum sativum genotypes was induced upon interaction with Glomus mosseae. The amplitude of this accumulation was higher in P2 plants and increased with time, an effect that was not observed in roots
of the wild-type P. sativum genotype. Likewise, Rhizobium leguminosarum wild type or a mutant blocked in Nod factor biosynthesis induced SA accumulation in P2, whereas SA accumulation in roots
of the wild-type plant was dependent on the inability of the bacterium to produce Nod factors. These results suggest that
the sym30 gene, which is mutated in P2 plants, could be implicated in a common pathway that leads to the suppression of an SA-dependent
defence mechanism in legume plants against Rhizobium and endomycorrhizal fungi, thus allowing establishment of symbiosis.
Plant nonspecific lipid-transfer proteins stimulate the transfer of a broad range of lipids between membranes in vitro. In view of their ability to inhibit bacterial and fungal pathogens, their distribution at high concentrations over exposed surfaces and in the vascular system, and the response of Ltp-gene expression to infection with pathogens, they are now thought to be active plant-defense proteins.
The cloning and sequence analysis of a gene that encodes a lipid transfer protein (LTP) from rice is reported. A genomic DNA library from Oryza sativa was screened using a cDNA encoding a maize LTP. One genomic clone containing the gene (Ltp) was partially sequenced and analyzed. The open reading frame is interrupted by an 89-bp intron. From the results of Southern hybridizations, Ltp appears to be a member of a small multigenic family. Transcripts of the corresponding gene were detected in several tissues including coleoptile, leaf, endosperm, scutellum and root. The transcription start point was determined by primer extension. The deduced amino-acid sequence of the Ltp product is shown to be homologous to LTPs from other crops.
Clones for three barley non-specific lipid transfer proteins (LTP2, LTP3, and LTP4; formerly Cw18, Cw20 and Cw21, respectively) which had been previously shown to inhibit growth of plant pathogens, were selected and characterized from a cDNA library derived from young etiolated leaves. Genes Ltp2 and Ltp4 were located in chromosome 3H and gene Ltp3 was assigned to chromosome 7H by Southern blot analysis of wheat-barley disomic addition lines, using gene-specific probes (3'-ends of cDNAs). These assignments were confirmed by the polymerase chain reaction, using specific primers. The three genes were expressed in stem, shoot apex, leaves and roots (at low levels) throughout development. Genes Ltp3 and Ltp4 were expressed at high levels, and Lpt2 at low levels, in the spike (rachis, lemma plus palea and grain coats). Neither of the mRNAs was detected in endosperm. The proteins were localized by tissue-printing with polyclonal antibodies in the outer cell layer of the exposed surfaces of the plant, throughout the embryo, and in vascular tissues. Expression levels in leaves were moderately increased by 0.34 M NaCl and by 0.1 mM abscisic acid and were not affected by cold, drought, salicylate, 2,6-dichloro-isonicotinic acid, ethylene or ethephon. Methyl Jasmonate (10 microM) switched off all three genes. Inoculation with Av6 or vir6 isolates of the fungal pathogen Erysiphe graminis increased the three mRNAs, especially that of LTP4, which reached a maximum nine-fold increase 12-16 h after infection.
Phenylalanine ammonia-lyase (PAL) genomic sequences were isolated from a rice (Oryza sativa L.) genomic library using a PCR-amplified rice PAL DNA fragment as a probe. There is a small family of PAL genes in the rice genome. The nucleotide sequence of one PAL gene, ZB8, was determined. The ZB8 gene is 4660 bp in length and consists of two exons and one intron. It encodes a polypeptide of 710 amino acids. The transcription start site was 137 bp upstream from the translation initiation site. Rice PAL transcripts accumulated to a high level in stems, with lower levels in roots and leaves. Wounding of leaf tissues induced ZB8 PAL transcripts to a high level. In rice suspension-cultured cells treated with fungal cell wall elicitors, the ZB8 PAL transcript increased within 30 min and reached maximum levels in 1-2 h. The transcription of the ZB8 gene was investigated by fusing its promoter to the reporter gene beta-glucuronidase (GUS) and transforming the construct into rice and tobacco plants, as well as rice suspension-cultured cells. High levels of GUS activity were observed in stems, moderate levels in roots and low levels in leaves of transgenic rice and tobacco plants. Histochemical analysis indicated that in transgenic rice the promoter was active in root apical tips, lateral root initiation sites, and vascular and epidermal tissues of stems and roots. In rice flowers, high GUS activity was observed in floral shoots, receptacles, anthers and filaments, occasionally GUS activity was also detected in lemma and awn tissues. In tobacco flowers, high GUS activity was detected in the pink part of petals. Consistent with the activity of endogenous PAL transcripts, wounding of rice and tobacco leaf tissues induced GUS activity from low basal levels. Tobacco mosaic virus (TMV) infection of tobacco leaves induced GUS activity to a high level. Fungal cell wall elicitors strongly induced GUS activity and GUS transcripts to high levels in transgenic rice suspension-cultured cells. We demonstrated that the promoter of ZB8 gene is both developmentally regulated and stress-inducible.
Several cDNA clones encoding three different lipid transfer proteins (LTPs) have been isolated from rice (Oryza sativa L.) in order to analyse the complexity, the evolution and the expression of the LTP gene family. The mature proteins deduced from three clones exhibited a molecular mass of 9 kDa, in agreement with the molecular mass of other LTPs from plants. The clones were shown to be homologous in the coding region, while the 3' non-coding regions diverged strongly between the clones. The occurrence of at least three small multigene families encoding these proteins in rice was confirmed by Southern blot analysis. When compared with each other and with LTPs from other plants, the cluster including rice LTPs and other cereal LTPs indicated that these genes duplicated rather recently and independently in the different plant phyla. The expression pattern of each gene family was also investigated. Northern blot experiments demonstrated that they are differentially regulated in the different tissues analysed. Components such as salt, salicylic acid and abscisic acid were shown to modulate Ltp gene expression, depending on tissues and gene classes, suggesting a complex regulation of these genes.
Infection of plants by necrotizing pathogens can induce broad-spectrum resistance to subsequent pathogen infection. This systemic acquired resistance (SAR) is thought to be triggered by a vascular-mobile signal that moves throughout the plant from the infected leaves. A considerable amount of evidence suggests that salicylic acid (SA) is involved in the induction of SAR. Because SA is found in phloem exudate of infected cucumber and tobacco plants, it has been proposed as a candidate for the translocated signal. To determine if SA is the mobile signal, grafting experiments were performed using transgenic plants that express a bacterial SA-degrading enzyme. We show that transgenic tobacco root-stocks, although unable to accumulate SA, were fully capable of delivering a signal that renders nontransgenic scions resistant to further pathogen infection. This result indicated that the translocating, SAR-inducing signal is not SA. Reciprocal grafts demonstrated that the signal requires the presence of SA in tissues distant from the infection site to induce systemic resistance.
Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts (as much as 4% of the total soluble proteinss) in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant proteins.
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