Jasmonate Accumulation Research Articles

Attenuated accumulation of jasmonates modifies stomatal responses to water deficit.

To determine whether drought-induced root jasmonate [jasmonic acid (JA) and jasmonic acid-isoleucine (JA-Ile)] accumulation affected shoot responses to drying soil, near-isogenic wild-type (WT) tomato (Solanum lycopersicum cv. Castlemart) and the def-1 mutant (which fails to accumulate jasmonates during water deficit) were self- and reciprocally grafted. Rootstock hydraulic conductance was entirely rootstock dependent and significantly lower in def-1, yet def-1 scions maintained a higher leaf water potential as the soil dried due to their lower stomatal conductance (gs). Stomatal sensitivity to drying soil (the slope of gsversus soil water content) was low in def-1 self-grafts but was normalized by grafting onto WT rootstocks. Although soil drying increased 12-oxo-phytodienoic acid (OPDA; a JA precursor and putative antitranspirant) concentrations in def-1 scions, foliar JA accumulation was negligible and foliar ABA accumulation reduced compared with WT scions. A WT rootstock increased drought-induced ABA and JA accumulation in def-1 scions, but decreased OPDA accumulation. Xylem-borne jasmonates were biologically active, since supplying exogenous JA via the transpiration stream to detached leaves decreased transpiration of WT seedlings but had the opposite effect in def-1. Thus foliar accumulation of both ABA and JA at WT levels is required for both maximum (well-watered) gs and stomatal sensitivity to drying soil.

Linking jasmonates with pigment accumulation and photoprotection in a high-mountain endemic plant, Saxifraga longifolia

Jasmonates are widely found in the plant kingdom and play a key role in both plant biotic and abiotic defense and plant development. Jasmonates activity under abiotic stress conditions have been extensively investigated in model plants, but little is known about the bioactive forms and their functions in non-model species, particularly in plants growing in their natural environment. Here, we performed a jasmonate profiling approach to unravel changes in the specific jasmonate signature of leaves as a function of environmental conditions, including the measurement of both free and conjugated forms of jasmonates by UHPLC–MS/MS, during the summer and autumn in Saxifraga longifolia plants growing in their natural habitat in the Pyrenees. We evaluated the climatological factors governing specific jasmonate signatures and the correlation between jasmonate accumulation and leaf morphology, PSII efficiency and pigment accumulation, including anthocyanins, chlorophylls and carotenoids. The results showed a jasmonate profiling characterized by an accumulation of free jasmonic acid and its precursor, 12-oxo-phytodienoic acid, with the amino acid conjugated forms being much less abundant. Among amino acid conjugates, jasmonoyl-isoleucine, jasmonoyl-valine and jasmonoyl-phenylalanine were the most abundant forms. Contents of 12-oxo-phytodienoic acid decreased, while those of free jasmonic acid increased during summer drought stress events. The five amino acid conjugated forms did respond similarly to environmental changes with progressive decreases from summer to autumn, but irrespective of drought events. Endogenous contents of free jasmonic acid correlated positively with those of anthocyanins. Furthermore, exogenous jasmonate applications on leaves increased anthocyanin contents, thus confirming a link between jasmonates and anthocyanin accumulation in S. longifolia plants.

Drought stress promotes the colonization success of a herbivorous mite that manipulates plant defenses

Climate change is expected to bring longer periods of drought and this may affect the plant’s ability to resist pests. We assessed if water deficit affects the tomato russet mite (TRM; Aculops lycopersici), a key tomato-pest. TRM thrives on tomato by suppressing the plant’s jamonate defenses while these defenses typically are modulated by drought stress. We observed that the TRM population grows faster and causes more damage on drought-stressed plants. To explain this observation we measured several nutrients, phytohormones, defense-gene expression and the activity of defensive proteins in plants with or without drought stress or TRM. TRM increased the levels of total protein and several free amino acids. It also promoted the SA-response and upregulated the accumulation of jasmonates but down-regulated the downstream marker genes while promoting the activity of cysteine—but not serine—protease inhibitors, polyphenol oxidase and of peroxidase (POD). Drought stress, in turn, retained the down regulation of JA-marker genes and reduced the activity of serine protease inhibitors and POD, and altered the levels of some free-amino acids. When combined, drought stress antagonized the accumulation of POD and JA by TRM and synergized accumulation of free sugars and SA. Our data show that drought stress interacts with pest-induced primary and secondary metabolic changes and promotes pest performance.

GhJAZ2 attenuates cotton resistance to biotic stresses via the inhibition of the transcriptional activity of GhbHLH171.

Plants have evolved effective mechanisms to protect themselves against multiple stresses, and employ jasmonates (JAs) as vital defence signals to defend against pathogen infection. The accumulation of JA, induced by signals from biotic and abiotic stresses, results in the degradation of Jasmonate-ZIM-domain (JAZ) proteins, followed by the de-repression of JAZ-repressed transcription factors (such as MYC2) to activate defence responses and developmental processes. Here, we characterized a JAZ family protein, GhJAZ2, from cotton (Gossypium hirsutum) which was induced by methyl jasmonate (MeJA) and inoculation of Verticillium dahliae. The overexpression of GhJAZ2 in cotton impairs the sensitivity to JA, decreases the expression level of JA-response genes (GhPDF1.2 and GhVSP) and enhances the susceptibility to V.dahliae and insect herbivory. Yeast two-hybrid and bimolecular fluorescence complementation assays showed that GhJAZ2 may be involved in the regulation of cotton disease resistance by interaction with further disease-response proteins, such as pathogenesis-related protein GhPR10, dirigent-like protein GhD2, nucleotide-binding site leucine-rich repeat (NBS-LRR) disease-resistant protein GhR1 and a basic helix-loop-helix transcription factor GhbHLH171. Unlike MYC2, overexpression of GhbHLH171 in cotton activates the JA synthesis and signalling pathway, and improves plant tolerance to the fungus V.dahliae. Molecular and genetic evidence shows that GhJAZ2 can interact with GhbHLH171 and inhibit its transcriptional activity and, as a result, can restrain the JA-mediated defence response. This study provides new insights into the molecular mechanisms of GhJAZ2 in the regulation of the cotton defence response.

Involvement of jasmonates in responses of sunflower (Helianthus annuus) seedlings to moderate water stress

Jasmonates (JAs), a type of phytohormone, are involved in sensing and signaling of several environmental stresses (biotic and abiotic). Jasmonic acid (JA) has been suggested to function in plant responses to drought, because this type of stress induces expression of several genes that also respond to JA. We investigated the involvement of JA and its precursor (12-oxo-phytodienoic acid; OPDA) on seedling morphological and physiological characteristics of two sunflower (Helianthus annuus) inbred lines with contrasting responses (sensitive vs. tolerant) to water stress. Our experimental treatments were based on moderate water stress (simulated by application of mannitol 400 mM) and on blocking of JA biosynthesis (by the chemical inhibitor salicylhydroxamic acid; SHAM). Water stress resulted in reduction of primary root (PR) growth and lateral root (LR) growth, but in increased LR number. SHAM treatment increased PR length, LR number, and LR length, thus strongly affecting root architecture. Water stress had differential effects on various physiological parameters, including relative water content (RWC), stomatal conductance, and content of photosynthetic pigments (chlorophylls, carotenoids). OPDA and JA accumulation in aerial part and roots induced by water stress was reversed by combined water stress plus SHAM treatment at day 14. Our findings suggest that SHAM effectively inhibits de novo JA biosynthesis induced by water stress, and that JAs play a protective role in responses of sunflower seedlings to this stress. JAs, particularly OPDA, are highly effective signaling molecules in mediation of sunflower seedling responses to water stress.

Triggering a false alarm: wounding mimics prey capture in the carnivorous Venus flytrap (Dionaea muscipula).

In the carnivorous plant Venus flytrap (Dionaea muscipula), the sequence of events after prey capture resembles the well-known plant defence signalling pathway in response to pathogen or herbivore attack. Here, we used wounding to mimic prey capture to show the similarities and differences between botanical carnivory and plant defence mechanisms. We monitored movement, electrical signalling, jasmonate accumulation and digestive enzyme secretion in local and distal (systemic) traps in response to prey capture, the mechanical stimulation of trigger hairs and wounding. The Venus flytrap cannot discriminate between wounding and mechanical trigger hair stimulation. Both induced the same action potentials, rapid trap closure, hermetic trap sealing, the accumulation of jasmonic acid (JA) and its isoleucine conjugate (JA-Ile), and the secretion of proteases (aspartic and cysteine proteases), phosphatases and type I chitinase. The jasmonate accumulation and enzyme secretion were confined to the local traps, to which the stimulus was applied, which correlates with the propagation of electrical signals and the absence of a systemic response in the Venus flytrap. In contrast to plant defence mechanisms, the absence of a systemic response in carnivorous plant may represent a resource-saving strategy. During prey capture, it could be quite expensive to produce digestive enzymes in the traps on the plant without prey.

Effect of methyl jasmonic acid on peach fruit ripening progress

In order to investigate the role of jasmonates (JAs) during the ripening of peach fruit, two concentrations of methyl jasmonate (MeJA, 10 and 100mM) were evaluated using field system. Fruit quality parameters, such as the contents of anthocyanin, volatile compounds and cell wall enzymes, and the transcriptional profiles of several ripening-related genes were analyzed. Our results showed that MeJA promoted fruit chlorophyll degradation and anthocyanin accumulation, volatile compounds enhancement, but it would also delay fruit softening through regulation cell wall enzymes activities of PG and cellulase. MeJA increased fruit anti-stress because of the promotion of SOD, POD, CAT, PPO enzyme activities. MeJA reduced fruit endogenous ethylene content, although ethylene accelerated fruit softening and decreased titratable acidity that resulted in fruit ripening. MeJA altered the expression profiles of its biosynthesis pathway genes of PpLOX, PpAOS, and PpOPR3, which resulted the accumulation of JA accumulation in peach fruit. MeJA also increased the expression levels of anthocyanin-associated genes PpMYB, PpPAL, PpCHS, PpCHI, PpF3H, PpDFR, and PpUFGT. MeJA increased chlorophyll degradation gene of PpPAO, as well as decreased its biosynthesis gene of PpPORC, which led to chlorophyll reduction. However, ethylene had a reverse effect on the genes’ expression levels, and it inhibited anthocyanin accumulation. Ultimately, heterologous expression peach PpAOS in strawberry showed that JA promoted fruit anthocyanin accumulation. The present findings suggest that JA promotes peach fruit ripening through regulation anthocyanin accumulation, which is different from the way triggered by ethylene in regulation peach fruit ripening.

Jasmonate Regulates Plant Responses to Postsubmergence Reoxygenation through Transcriptional Activation of Antioxidant Synthesis.

Submergence induces hypoxia in plants; exposure to oxygen following submergence, termed reoxygenation, produces a burst of reactive oxygen species. The mechanisms of hypoxia sensing and signaling in plants have been well studied, but how plants respond to reoxygenation remains unclear. Here, we show that reoxygenation in Arabidopsis (Arabidopsis thaliana) involves rapid accumulation of jasmonates (JAs) and increased transcript levels of JA biosynthesis genes. Application of exogenous methyl jasmonate improved tolerance to reoxygenation in wild-type Arabidopsis; also, mutants deficient in JA biosynthesis and signaling were very sensitive to reoxygenation. Moreover, overexpression of the transcription factor gene MYC2 enhanced tolerance to posthypoxic stress, and myc2 knockout mutants showed increased sensitivity to reoxygenation, indicating that MYC2 functions as a key regulator in the JA-mediated reoxygenation response. MYC2 transcriptionally activates members of the VITAMIN C DEFECTIVE (VTC) and GLUTATHIONE SYNTHETASE (GSH) gene families, which encode rate-limiting enzymes in the ascorbate and glutathione synthesis pathways. Overexpression of VTC1 and GSH1 in the myc2-2 mutant suppressed the posthypoxic hypersensitive phenotype. The JA-inducible accumulation of antioxidants may alleviate oxidative damage caused by reoxygenation, improving plant survival after submergence. Taken together, our findings demonstrate that JA signaling interacts with the antioxidant pathway to regulate reoxygenation responses in Arabidopsis.

The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis.

The carnivorous sundew plant (Drosera capensis) captures prey using sticky tentacles. We investigated the tentacle and trap reactions in response to the electrical and jasmonate signalling evoked by different stimuli to reveal how carnivorous sundews recognize digestible captured prey in their traps. We measured the electrical signals, phytohormone concentration, enzyme activities and Chla fluorescence in response to mechanical stimulation, wounding or insect feeding in local and systemic traps. Seven new proteins in the digestive fluid were identified using mass spectrometry. Mechanical stimuli and live prey induced a fast, localized tentacle-bending reaction and enzyme secretion at the place of application. By contrast, repeated wounding induced a nonlocalized convulsive tentacle movement and enzyme secretion in local but also in distant systemic traps. These differences can be explained in terms of the electrical signal propagation and jasmonate accumulation, which also had a significant impact on the photosynthesis in the traps. The electrical signals generated in response to wounding could partially mimic a mechanical stimulation of struggling prey and might trigger a false alarm, confirming that the botanical carnivory and plant defence mechanisms are related. To trigger the full enzyme activity, the traps must detect chemical stimuli from the captured prey.

Control of sexuality by the sk1-encoded UDP-glycosyltransferase of maize.

Sex determination in maize involves the production of staminate and pistillate florets from an initially bisexual floral meristem. Pistil elimination in staminate florets requires jasmonic acid signaling, and functional pistils are protected by the action of the silkless 1 (sk1) gene. The sk1 gene was identified and found to encode a previously uncharacterized family 1 uridine diphosphate glycosyltransferase that localized to the plant peroxisomes. Constitutive expression of an sk1 transgene protected all pistils in the plant, causing complete feminization, a gain-of-function phenotype that operates by blocking the accumulation of jasmonates. The segregation of an sk1 transgene was used to effectively control the production of pistillate and staminate inflorescences in maize plants.

Expression profiles of genes involved in jasmonic acid biosynthesis and signaling during growth and development of carrot.

Jasmonates (JAs) are recognized as essential regulators in response to environmental stimuli and plant development. Carrot is an Apiaceae vegetable with great value and undergoes significant size changes over the course of plant growth. However, JA accumulation and its potential roles in carrot growth remain unclear. Here, methyl JA (MeJA) levels and expression profiles of JA-related genes were analyzed in carrot roots and leaves at five developmental stages. MeJA levels in the roots and leaves were the highest at the first stage and decreased as carrot growth proceeded. Transcript levels of several JA-related genes (Dc13-LOX1, Dc13-LOX2, DcAOS, DcAOC, DcOPR2, DcOPR3, DcOPCL1, DcJAR1, DcJMT, DcCOI1, DcJAZ1, DcJAZ2, DcMYC2, DcCHIB/PR3, DcLEC, and DcVSP2) were not well correlated with MeJA accumulation during carrot root and leaf development. In addition, some JA-related genes (DcJAR1, DcJMT, DcCOI1, DcMYC2, and DcVSP2) showed differential expression between roots and leaves. These results suggest that JAs may regulate carrot plant growth in stage-dependent and organ-specific manners. Our work provides novel insights into JA accumulation and its potential roles during carrot growth and development.

GhERF-IIb3 regulates the accumulation of jasmonate and leads to enhanced cotton resistance to blight disease.

The phytohormone jasmonic acid (JA) and its derivatives, collectively referred to as jasmonates, regulate many developmental processes, but are also involved in the response to numerous abiotic/biotic stresses. Thus far, powerful reverse genetic strategies employing perception, signalling or biosynthesis mutants have broadly contributed to our understanding of the role of JA in the plant stress response and development, as has the chemical gain-of-function approach based on exogenous application of the hormone. However, there is currently no method that allows for tightly controlled JA production in planta. By investigating the control of the JA synthesis pathway in bacteria-infected cotton (Gossypium hirsutum L.) plants, we identified a transcription factor (TF), named GhERF-IIb3, which acts as a positive regulator of the JA pathway. Expression of this well-conserved TF in cotton leaves was sufficient to produce in situ JA accumulation at physiological concentrations associated with an enhanced cotton defence response to bacterial infection.

Slow food: insect prey and chitin induce phytohormone accumulation and gene expression in carnivorous Nepenthes plants.

Carnivorous Nepenthes plants use modified leaves forming pitfall traps to capture and digest prey, mainly insects, for additional nutrient supply. These traps, so called pitchers, contain a plant-derived fluid composed of many hydrolytic enzymes and defence-related proteins. In this study, the prey-induced induction of corresponding genes of those proteins and a role for phytohormones in this process was analysed. Tissue from insect prey-fed, chitin- and phytohormone-challenged pitchers was harvested and analysed for selected gene expressions by a quantitative PCR technique. Phytohormone levels were determined by LC-MS/MS. Nepenthesin proteolytic activities were measured in the digestive fluid using a fluorescence substrate. Insect prey in the pitchers induced the accumulation of phytohormones such as jasmonates as well as the transcription of studied genes encoding a chitinase 3 and a protease (nepenthesin I), whereas a defence-related protein (PR-1) gene was not induced. Treatment with chitin as a component of the insects' exoskeleton triggered the accumulation of jasmonates, the expression of nepenthesin I and chitinase 3 genes similar to jasmonic acid treatment, and induced protease activity in the fluid. All detectable responses were slowly induced. The results suggest that upon insect prey catch a sequence of signals is initiated: (1) insect-derived chitin, (2) jasmonate as endogenous phytohormone signal, (3) the induction of digestive gene expression and (4) protein expression. This resembles a similar hierarchy of events as described from plant pathogen/herbivore interactions, supporting the idea that carnivory evolved from plant defences.

Synthesis, metabolism and systemic transport of a fluorinated mimic of the endogenous jasmonate precursor OPC-8:0

Jasmonates (JAs) are fatty acid derivatives that mediate many developmental processes and stress responses in plants. Synthetic jasmonate derivatives (commonly isotopically labeled), which mimic the action of the endogenous compounds are often employed as internal standards or probes to study metabolic processes. However, stable-isotope labeling of jasmonates does not allow the study of spatial and temporal distribution of these compounds in real time by positron emission tomography (PET). In this study, we explore whether a fluorinated jasmonate could mimic the action of the endogenous compound and therefore, be later employed as a tracer to study metabolic processes by PET. We describe the synthesis and the metabolism of (Z)-7-fluoro-8-(3-oxo-2-(pent-2-en-1-yl)cyclopentyl)octanoic acid (7F-OPC-8:0), a fluorinated analog of the JA precursor OPC-8:0. Like endogenous jasmonates, 7F-OPC-8:0 induces the transcription of marker jasmonate responsive genes (JRG) and the accumulation of jasmonates after its application to Arabidopsis thaliana plants. By using UHPLC–MS/MS, we could show that 7F-OPC-8:0 is metabolized in vivo similarly to the endogenous OPC-8:0. Furthermore, the fluorinated analog was successfully employed as a probe to show its translocation to undamaged systemic leaves when it was applied to wounded leaves. This result suggests that OPC-8:0 – and maybe other oxylipins – may contribute to the mobile signal which triggers systemic defense responses in plants. We highlight the potential of fluorinated oxylipins to study the mode of action of lipid-derived molecules in planta, either by conventional analytical methods or fluorine-based detection techniques.

MeJA Affects Root Growth by Modulation of Transmembrane Auxin Flux in the Transition Zone

Biosynthesis and accumulation of jasmonate (JA) can regulate plant defense responses and organ development under insect herbivore stress conditions. One of these responses, the inhibition of root growth, is a common phenomenon. However, the physiological and molecular mechanisms of how JA affects root growth are not completely understood. In this study, the influence of MeJA treatment on auxin and proton flux rates in the root apex region of Col-0, coi1-1, pin2, and aux1-7 mutant lines was examined using a non-invasive micro-test technique. The auxin and H+ flux profiles taken from coi1-1 mutants suggest that the modulation of auxin and H+ flux by JA requires the function of COI1. The auxin and H+ flux in pin2 and aux1 mutants with and without JA treatment suggest that JA can affect polar auxin transport by regulating PIN-mediated auxin efflux and the AUX-mediated influx pathways. Furthermore, the expression levels of PIN1, PIN2, PIN3, PIN7, AUX1, and TIR1 genes were reduced under MeJA treatment, and expression levels of CYP79B2 and CYP79B3 were elevated. Together, these results suggest that JA signaling may modulate the auxin signaling pathways by regulating the expression of key genes.

Navigating natural variation in herbivory-induced secondary metabolism in coyote tobacco populations using MS/MS structural analysis

Natural variation can be extremely useful in unraveling the determinants of phenotypic trait evolution but has rarely been analyzed with unbiased metabolic profiling to understand how its effects are organized at the level of biochemical pathways. Native populations of Nicotiana attenuata, a wild tobacco species, have been shown to be highly genetically diverse for traits important for their interactions with insects. To resolve the chemodiversity existing in these populations, we developed a metabolomics and computational pipeline to annotate leaf metabolic responses to Manduca sexta herbivory. We selected seeds from 43 accessions of different populations from the southwestern United States--including the well-characterized Utah 30th generation inbred accession--and grew 183 plants in the glasshouse for standardized herbivory elicitation. Metabolic profiles were generated from elicited leaves of each plant using a high-throughput ultra HPLC (UHPLC)-quadrupole TOFMS (qTOFMS) method, processed to systematically infer covariation patterns among biochemically related metabolites, as well as unknown ones, and finally assembled to map natural variation. Navigating this map revealed metabolic branch-specific variations that surprisingly only partly overlapped with jasmonate accumulation polymorphisms and deviated from canonical jasmonate signaling. Fragmentation analysis via indiscriminant tandem mass spectrometry (idMS/MS) was conducted with 10 accessions that spanned a large proportion of the variance found in the complete accession dataset, and compound spectra were computationally assembled into spectral similarity networks. The biological information captured by this networking approach facilitates the mining of the mass spectral data of unknowns with high natural variation, as demonstrated by the annotation of a strongly herbivory-inducible phenolic derivative, and can guide pathway analysis.

A Nicotiana attenuata cell wall invertase inhibitor (NaCWII) reduces growth and increases secondary metabolite biosynthesis in herbivore-attacked plants.

Plant invertases are sucrolytic enzymes that are essential for the regulation of carbohydrate metabolism and source-sink relationships. While their activity has been well documented during abiotic and biotic stresses, the role of proteinaceous invertase inhibitors in regulating these changes is unknown. Here, we identify a putative Nicotiana attenuata cell wall invertase inhibitor (NaCWII) which is strongly up-regulated in a jasmonate (JA)-dependent manner following simulated attack by the specialist herbivore Manduca sexta. To understand the role of NaCWII in planta, we silenced its expression by RNA interference and measured changes in primary and secondary metabolism and plant growth following simulated herbivory. NaCWII-silenced plants displayed a stronger depletion of carbohydrates and a reduced capacity to increase secondary metabolite pools relative to their empty vector control counterparts. This coincided with the attenuation of herbivore-induced CWI inhibition and growth suppression characteristic of wild-type plants. Together our findings suggest that NaCWII may act as a regulatory switch located downstream of JA accumulation which fine-tunes the plant's balance between growth and defense metabolism under herbivore attack. Although carbohydrates are not typically viewed as key factors in plant growth and defense, our study shows that interfering with their catabolism strongly influences plant responses to herbivory.

A novel insight into the cost-benefit model for the evolution of botanical carnivory.

The cost-benefit model for the evolution of botanical carnivory provides a conceptual framework for interpreting a wide range of comparative and experimental studies on carnivorous plants. This model assumes that the modified leaves called traps represent a significant cost for the plant, and this cost is outweighed by the benefits from increased nutrient uptake from prey, in terms of enhancing the rate of photosynthesis per unit leaf mass or area (AN) in the microsites inhabited by carnivorous plants. This review summarizes results from the classical interpretation of the cost-benefit model for evolution of botanical carnivory and highlights the costs and benefits of active trapping mechanisms, including water pumping, electrical signalling and accumulation of jasmonates. Novel alternative sequestration strategies (utilization of leaf litter and faeces) in carnivorous plants are also discussed in the context of the cost-benefit model. Traps of carnivorous plants have lower AN than leaves, and the leaves have higher AN after feeding. Prey digestion, water pumping and electrical signalling represent a significant carbon cost (as an increased rate of respiration, RD) for carnivorous plants. On the other hand, jasmonate accumulation during the digestive period and reprogramming of gene expression from growth and photosynthesis to prey digestion optimizes enzyme production in comparison with constitutive secretion. This inducibility may have evolved as a cost-saving strategy beneficial for carnivorous plants. The similarities between plant defence mechanisms and botanical carnivory are highlighted.

Mutualistic root endophytism is not associated with the reduction of saprotrophic traits and requires a noncompromised plant innate immunity.

During a compatible interaction, the sebacinoid root-associated fungi Piriformospora indica and Sebacina vermifera induce modification of root morphology and enhance shoot growth in Arabidopsis thaliana. The genomic traits common in these two fungi were investigated and compared with those of other root-associated fungi and saprotrophs. The transcriptional responses of the two sebacinoid fungi and of Arabidopsis roots to colonization at three different symbiotic stages were analyzed by custom-designed microarrays. We identified key genomic features characteristic of sebacinoid fungi, such as expansions for gene families involved in hydrolytic activities, carbohydrate-binding and protein-protein interaction. Additionally, we show that colonization of Arabidopsis correlates with the induction of salicylic acid catabolism and accumulation of jasmonate and glucosinolates (GSLs). Genes involved in root developmental processes were specifically induced by S. vermifera at later stages during interaction. Using different Arabidopsis indole-GSLs mutants and measurement of secondary metabolites, we demonstrate the importance of the indolic glucosinolate pathway in the growth restriction of P. indica and S. vermifera and we identify indole-phytoalexins and specifically indole-carboxylic acids derivatives as potential key players in the maintenance of a mutualistic interaction with root endophytes.

Interplay between vitamin E and phosphorus availability in the control of longevity in Arabidopsis thaliana.

Vitamin E helps to control the cellular redox state by reacting with singlet oxygen and preventing the propagation of lipid peroxidation in thylakoid membranes. Both plant ageing and phosphorus deficiency can trigger accumulation of reactive oxygen species, leading to damage to the photosynthetic apparatus. This study investigates how phosphorus availability and vitamin E interact in the control of plant longevity in the short-lived annual Arabidopsis thaliana. The responses of tocopherol cyclase (VTE1)- and γ-tocopherol methyltransferase (VTE4)-null mutants to various levels of phosphorus availability was compared with that of wild-type plants. Longevity (time from germination to rosette death) and the time taken to pass through different developmental stages were determined, and measurements were taken of photosynthetic efficiency, pigment concentration, lipid peroxidation, vitamin E content and jasmonate content. The vte1 mutant showed accelerated senescence under control conditions, excess phosphorus and mild phosphorus deficiency, suggesting a delaying, protective effect of α-tocopherol during plant senescence. However, under severe phosphorus deficiency the lack of α-tocopherol paradoxically increased longevity in the vte1 mutant, while senescence was accelerated in wild-type plants. Reduced photoprotection in vitamin E-deficient mutants led to increased levels of defence chemicals (as indicated by jasmonate levels) under severe phosphorus starvation in the vte4 mutant and under excess phosphorus and mild phosphorus starvation in the vte1 mutant, indicating a trade-off between the capacity for photoprotection and the activation of chemical defences (jasmonate accumulation). Vitamin E increases plant longevity under control conditions and mild phosphorus starvation, but accelerates senescence under severe phosphorus limitation. Complex interactions are revealed between phosphorus availability, vitamin E and the potential to synthesize jasmonates, suggesting a trade-off between photoprotection and the activation of chemical defences in the plants.