A pair of receptor-like kinases is responsible for natural variation in shoot growth response to mannitol treatment in Arabidopsis thaliana.

SUMMARY Growth is a complex trait that adapts to the prevailing conditions by integrating many internal and external signals. Understanding the molecular origin of this variation remains a challenging issue. In this study, natural variation of shoot growth under mannitol-induced stress was analyzed by standard quantitative trait locus mapping methods in a recombinant inbred line population derived from a cross between the Col-0 and Cvi-0 Arabidopsis thaliana accessions. Cloning of a major QTL specific to mannitol-induced stress condition led to identification of EGM1 and EGM2, a pair of tandem-duplicated genes encoding receptor-like kinases that are potentially involved in signaling of mannitol-associated stress responses. Using various genetic approaches, we identified two non-synonymous mutations in the EGM2 [Cvi] allele that are shared by at least ten accessions from various origins and are probably responsible for a specific tolerance to mannitol. We have shown that the enhanced shoot growth phenotype contributed by the Cvi allele is not linked to generic osmotic properties but instead to a specific chemical property of mannitol itself. This result raises the question of the function of such a gene in A. thaliana, a species that does not synthesize mannitol. Our findings suggest that the receptor-like kinases encoded by EGM genes may be activated by mannitol produced by pathogens such as fungi, and may contribute to plant defense responses whenever mannitol is present

Distinct Roles of Jasmonates and Aldehydes in Plant-Defense Responses

BACKGROUND: Many inducible plant-defense responses are activated by jasmonates (JAs), C(6)-aldehydes, and their corresponding derivatives, produced by the two main competing branches of the oxylipin pathway, the allene oxide synthase (AOS) and hydroperoxide lyase (HPL) branches, respectively. In addition to competition for substrates, these branch-pathway-derived metabolites have substantial overlap in regulation of gene expression. Past experiments to define the role of C(6)-aldehydes in plant defense responses were biased towards the exogenous application of the synthetic metabolites or the use of genetic manipulation of HPL expression levels in plant genotypes with intact ability to produce the competing AOS-derived metabolites. To uncouple the roles of the C(6)-aldehydes and jasmonates in mediating direct and indirect plant-defense responses, we generated Arabidopsis genotypes lacking either one or both of these metabolites. These genotypes were subsequently challenged with a phloem-feeding insect (aphids: Myzus persicae), an insect herbivore (leafminers: Liriomyza trifolii), and two different necrotrophic fungal pathogens (Botrytis cinerea and Alternaria brassicicola). We also characterized the volatiles emitted by these plants upon aphid infestation or mechanical wounding and identified hexenyl acetate as the predominant compound in these volatile blends. Subsequently, we examined the signaling role of this compound in attracting the parasitoid wasp (Aphidius colemani), a natural enemy of aphids. PRINCIPAL FINDINGS: This study conclusively establishes that jasmonates and C(6)-aldehydes play distinct roles in plant defense responses. The jasmonates are indispensable metabolites in mediating the activation of direct plant-defense responses, whereas the C(6)-aldehyes are not. On the other hand, hexenyl acetate, an acetylated C(6)-aldehyde, is the predominant wound-inducible volatile signal that mediates indirect defense responses by directing tritrophic (plant-herbivore-natural enemy) interactions. SIGNIFICANCE: The data suggest that jasmonates and hexenyl acetate play distinct roles in mediating direct and indirect plant-defense responses. The potential advantage of this "division of labor" is to ensure the most effective defense strategy that minimizes incurred damages at a reduced metabolic cost

Genetic and molecular landscapes of the generalist phytopathogen Botrytis cinerea.

UNLABELLED: Botrytis cinerea Pers. Fr. (teleomorph: Botryotinia fuckeliana) is a necrotrophic fungal pathogen that attacks a wide range of plants. This updated pathogen profile explores the extensive genetic diversity of B. cinerea, highlights the progress in genome sequencing, and provides current knowledge of genetic and molecular mechanisms employed by the fungus to attack its hosts. In addition, we also discuss recent innovative strategies to combat B. cinerea. TAXONOMY: Kingdom: Fungi, phylum: Ascomycota, subphylum: Pezizomycotina, class: Leotiomycetes, order: Helotiales, family: Sclerotiniaceae, genus: Botrytis, species: cinerea. HOST RANGE: B. cinerea infects almost all of the plant groups (angiosperms, gymnosperms, pteridophytes, and bryophytes). To date, 1606 plant species have been identified as hosts of B. cinerea. GENETIC DIVERSITY: This polyphagous necrotroph has extensive genetic diversity at all population levels shaped by climate, geography, and plant host variation. PATHOGENICITY: Genetic architecture of virulence and host specificity is polygenic using multiple weapons to target hosts, including secretory proteins, complex signal transduction pathways, metabolites, and mobile small RNA. DISEASE CONTROL STRATEGIES: Efforts to control B. cinerea, being a high-diversity generalist pathogen, are complicated. However, integrated disease management strategies that combine cultural practices, chemical and biological controls, and the use of appropriate crop varieties will lessen yield losses. Recently, studies conducted worldwide have explored the potential of small RNA as an efficient and environmentally friendly approach for combating grey mould. However, additional research is necessary, especially on risk assessment and regulatory frameworks, to fully harness the potential of this technology

The glucosinolate–myrosinase system in an ecological and evolutionary context

International audienc

Distinct roles of jasmonates and aldehydes in plant-defense responses.

BackgroundMany inducible plant-defense responses are activated by jasmonates (JAs), C(6)-aldehydes, and their corresponding derivatives, produced by the two main competing branches of the oxylipin pathway, the allene oxide synthase (AOS) and hydroperoxide lyase (HPL) branches, respectively. In addition to competition for substrates, these branch-pathway-derived metabolites have substantial overlap in regulation of gene expression. Past experiments to define the role of C(6)-aldehydes in plant defense responses were biased towards the exogenous application of the synthetic metabolites or the use of genetic manipulation of HPL expression levels in plant genotypes with intact ability to produce the competing AOS-derived metabolites. To uncouple the roles of the C(6)-aldehydes and jasmonates in mediating direct and indirect plant-defense responses, we generated Arabidopsis genotypes lacking either one or both of these metabolites. These genotypes were subsequently challenged with a phloem-feeding insect (aphids: Myzus persicae), an insect herbivore (leafminers: Liriomyza trifolii), and two different necrotrophic fungal pathogens (Botrytis cinerea and Alternaria brassicicola). We also characterized the volatiles emitted by these plants upon aphid infestation or mechanical wounding and identified hexenyl acetate as the predominant compound in these volatile blends. Subsequently, we examined the signaling role of this compound in attracting the parasitoid wasp (Aphidius colemani), a natural enemy of aphids.Principal findingsThis study conclusively establishes that jasmonates and C(6)-aldehydes play distinct roles in plant defense responses. The jasmonates are indispensable metabolites in mediating the activation of direct plant-defense responses, whereas the C(6)-aldehyes are not. On the other hand, hexenyl acetate, an acetylated C(6)-aldehyde, is the predominant wound-inducible volatile signal that mediates indirect defense responses by directing tritrophic (plant-herbivore-natural enemy) interactions.SignificanceThe data suggest that jasmonates and hexenyl acetate play distinct roles in mediating direct and indirect plant-defense responses. The potential advantage of this "division of labor" is to ensure the most effective defense strategy that minimizes incurred damages at a reduced metabolic cost

A pair of receptor-like kinases is responsible for natural variation in shoot growth response to mannitol treatment in Arabidopsis thaliana.

Growth is a complex trait that adapts to the prevailing conditions by integrating many internal and external signals. Understanding the molecular origin of this variation remains a challenging issue. In this study, natural variation of shoot growth under mannitol-induced stress was analyzed by standard quantitative trait locus mapping methods in a recombinant inbred line population derived from a cross between the Col-0 and Cvi-0 Arabidopsis thaliana accessions. Cloning of a major QTL specific to mannitol-induced stress condition led to identification of EGM1 and EGM2, a pair of tandem-duplicated genes encoding receptor-like kinases that are potentially involved in signaling of mannitol-associated stress responses. Using various genetic approaches, we identified two non-synonymous mutations in the EGM2[Cvi] allele that are shared by at least ten accessions from various origins and are probably responsible for a specific tolerance to mannitol. We have shown that the enhanced shoot growth phenotype contributed by the Cvi allele is not linked to generic osmotic properties but instead to a specific chemical property of mannitol itself. This result raises the question of the function of such a gene in A. thaliana, a species that does not synthesize mannitol. Our findings suggest that the receptor-like kinases encoded by EGM genes may be activated by mannitol produced by pathogens such as fungi, and may contribute to plant defense responses whenever mannitol is present

Function of JAs and C₆-aldehydes in plant protection against necrotrophic fungus, <i>Botrytis cinerea.</i>

<p>Lesion development was monitored and compared between leaves isolated from (A) <i>HPL-OE</i> vs. Col, (B) <i>aos</i>-<i>hpl</i> vs. <i>aos-HPL-OE</i>, (C) <i>gl-1</i> vs. <i>aos-hpl</i>, at 48, 72 or 96 hours post inoculation (hpi) with <i>B. cinerea</i> conidia. Each bar graph represents average lesion diameter±SD of 24 inoculated leaves. All leaves lacking jasmonates (<i>aos-hpl</i>, <i>aos-HPL-OE)</i> show larger lesions as compared to those with a functional AOS (Col, <i>HPL-OE</i>, <i>gl-1</i>). The lesion sizes were not affected by the presence or absence of HPL-derived metabolites. For comparison, representative photographs of each genotype 72 hpi is shown. Graphs are the means±SD of 24 replicates for each genotype. Bar = 1 cm. (D) Analyses of camalexin accumulation levels for leaves collected at 72 hpi (<i>gl-1</i>, <i>aos-hpl</i> and <i>aos-HPL-OE</i>) or 96 hpi (Col and <i>HPL-OE</i>) show negligible levels of camalexin in all plant genotypes with dysfunctional <i>AOS.</i> The <i>HPL-OE</i> lines contain 30% less camalexin than that in Col lines, potentially because of the reduced JA levels in these plants. Graphs are the means±SD of 24 replicates for each genotype. Within any given treatment, bars with different letters indicate significant differences (<i>P</i><0.005, Tukey's test).</p

Profiling of the HPL- and AOS-branch pathways metabolites.

<p>(A) Levels of C₆-aldehydes, (B) JAs (JA+MeJA), and (C) 12-OPDA determined in non wounded (grey bar), or wounded leaves 2 hours after mechanical damage (black bar). Each measurement is derived from the mean±standard deviation (SD) of three independent biological replicates. (D) Characterization and quantification of GLVs by adsorptive headspace collection and GC-MS analyses performed on three repeats of three independent biological replicates from wounded and non wounded <i>Arabidopsis</i> genotypes show that hexenyl acetate is the predominant volatile produced in wounded leaves of plants with a functional <i>HPL</i>. Double-headed arrow represents a scale for signal intensity. (E) Analyses of the emission rate of hexenyl acetate in non wounded (grey bar) or mechanically wounded (black bar) <i>aos-HPL-OE</i> plants, performed three times on three independent biological replicates show that emission of hexenyl acetate is wound-inducible and transient.</p