Involvement of jasmonate- and salicylate-related signaling pathways for the production of specific herbivore-induced volatiles in plants

We compared volatiles from lima bean leaves (Phaseolus lunatus) infested by either beet armyworm (Spodoptera exigua), common armyworm [Mythimna (Pseudaletia) separata], or two-spotted spider mite (Tetranychus urticae). We also analyzed volatiles from the leaves treated with jasmonic acid (JA) and/or methyl salicylate (MeSA). The volatiles induced by aqueous JA treatment were qualitatively and quantitatively similar to those induced by S. exigua or M. separata damage. Furthermore, both S. exigua and aqueous JA treatment induced the expression of the same basic PR genes. In contrast, gaseous MeSA treatment, and aqueous JA treatment followed by gaseous MeSA treatment, induced volatiles that was qualitatively and quantitatively more similar to the T. urticae-induced volatiles than those induced by aqueous JA treatment. In addition, T. urticae damage resulted in the expression of the acidic and basic PR genes that were induced by gaseous MeSA treatment and by aqueous JA treatment, respectively. Based on these data, we suggest that in lima bean leaves, the JA-related signaling pathway is involved in the production of caterpillar-induced volatiles, while both the SA-related signaling pathway and the JA-related signaling pathway are involved in the production of T. urticae-induced volatiles.     

Ion channel-forming alamethicin is a potent elicitor of volatile biosynthesis and tendril coiling. Cross talk between jasmonate and salicylate signaling in lima bean

Alamethicin (ALA), a voltage-gated, ion channel-forming peptide mixture from Trichoderma viride, is a potent elicitor of the biosynthesis of volatile compounds in lima bean (Phaseolus lunatus). Unlike elicitation with jasmonic acid or herbivore damage, the blend of substances emitted comprises only the two homoterpenes, 4,11-dimethylnona-1,3,7-triene and 4,8,12-trimethyltrideca-1,3,7,11-tetraene, and methyl salicylate. Inhibition of octadecanoid signaling by aristolochic acid and phenidone as well as mass spectrometric analysis of endogenous jasmonate demonstrate that ALA induces the biosynthesis of volatile compounds principally via the octadecanoid-signaling pathway (20-fold increase of jasmonic acid). ALA also up-regulates salicylate biosynthesis, and the time course of the production of endogenous salicylate correlates well with the appearance of the methyl ester in the gas phase. The massive up-regulation of the SA-pathway (90-fold) interferes with steps in the biosynthetic pathway downstream of 12-oxophytodienoic acid and thereby reduces the pattern of emitted volatiles to compounds previously shown to be induced by early octadecanoids. ALA also induces tendril coiling in various species like Pisum, Lathyrus, and Bryonia, but the response appears to be independent from octadecanoid biosynthesis, because inhibitors of lipoxygenase and phospholipase A(2) do not prevent the coiling reaction.     

Octadecanoid-derived alteration of gene expression and the "oxylipin signature" in stressed barley leaves. Implications for different signaling pathways

Stress-induced gene expression in barley (Hordeum vulgare cv Salome) leaves has been correlated with temporally changing levels of octadecanoids and jasmonates, quantified by means of gas chromatography/mass spectrometry-single ion monitoring. Application of sorbitol-induced stress led to a low and transient rise of jasmonic acid (JA), its precursor 12-oxophytodienoic acid (OPDA), and the methyl esters JAME and OPDAME, respectively, followed by a large increase in their levels. JA and JAME peaked between 12 and 16 h, about 4 h before OPDA and OPDAME. However, OPDA accumulated up to a 2.5-fold higher level than the other compounds. Dihomo-JA and 9, 13-didehydro-OPDA were identified as minor components. Kinetic analyses revealed that a transient threshold of jasmonates or octadecanoids is necessary and sufficient to initiate JA-responsive gene expression. Although OPDA and OPDAME applied exogenously were metabolized to JA in considerable amounts, both of them can induce gene expression, as evidenced by those genes that did not respond to endogenously formed JA. Also, coronatine induces JA-responsive genes independently from endogenous JA. Application of deuterated JA showed that endogenous synthesis of JA is not induced by JA treatment. The data are discussed in terms of distinct signaling pathways.     

枇杷幼果内源一氧化氮和茉莉酸对低温胁迫的响应

以三年生抗寒性较弱的‘早钟6号’枇杷(Eriobotrya japonica Lindl. cv. Zaozhong No.6)容器苗为材料,采用一氧化氮合成酶抑制剂L-NAME、硝酸还原酶非专一性抑制剂NaN₃和一氧化氮清除剂cPTIO处理低温胁迫下的枇杷幼果,研究其处理对枇杷幼果内源一氧化氮(Nitric oxide,NO)和茉莉酸(Jasmonate acid,JA)含量的影响,探讨枇杷幼果内源NO与JA对低温胁迫的响应及其信号转导的关系。结果表明:低温胁迫可诱导枇杷幼果内源NO和JA含量增加,采用NO清除剂和合成酶抑制剂处理均抑制了低温胁迫下的枇杷幼果中过氧化氢酶(CAT,EC 1.11.1.6)、过氧化物酶(POD,EC 1.11.1.7)和超氧化物歧化酶(SOD,EC 1.15.1.1)的活性,使过氧化氢(Hydrogen peroxide,H₂O₂)和丙二醛(Malondialdehyde,MDA)含量增加,细胞膜脂的过氧化加剧,加重了低温胁迫对幼果的伤害,导致了幼果脂氧合酶(LOX,EC 1.13.11.12)和丙二烯氧化物合成酶(AOS,EC 4.2.l.92)活性下降,内源JA生物合成受阻。细胞内源NO变化与JA含量密切相关,它们在枇杷对低温胁迫的响应中可能存在信号交叉。     

Induced plant defense via volatile production is dependent on rhizobial symbiosis

Nitrogen-fixing rhizobia can substantially influence plant–herbivore interactions by altering plant chemical composition and food quality. However, the effects of rhizobia on plant volatiles, which serve as indirect and direct defenses against arthropod herbivores and as signals in defense-associated plant–plant and within-plant signaling, are still unstudied. We measured the release of jasmonic acid (JA)-induced volatiles of rhizobia-colonized and rhizobia-free lima bean plants (Fabaceae: Phaseolus lunatus L.) and tested effects of their respective bouquets of volatile organic compounds (VOCs) on a specialist insect herbivore (Mexican bean beetle; Coccinellidae: Epilachna varivestis Mulsant) in olfactometer choice trials. In a further experiment, we showed that VOC induction by JA reflects the plant responses to mechanical wounding and insect herbivory. Following induction with JA, rhizobia-colonized plants released significantly higher amounts of the shikimic acid-derived compounds, whereas the emission of compounds produced via the octadecanoid, mevalonate and non-mevalonate pathways was reduced. These changes affected the choice behavior of beetles as the preference of non-induced plants was much more pronounced for plants that were colonized by rhizobia. We showed that indole likely represents the causing agent for the observed repellent effects of jasmonic acid-induced VOCs of rhizobia-colonized lima bean plants. Our study demonstrates a rhizobia-triggered efficacy of induced plant defense via volatiles. Due to these findings, we interpret rhizobia as an integral part of legume defenses against herbivores.     

Effects of feeding Spodoptera littoralis on lima bean leaves: IV. Diurnal and nocturnal damage differentially initiate plant volatile emission

Continuous mechanical damage initiates the rhythmic emission of volatiles in lima bean (Phaseolus lunatus) leaves; the emission resembles that induced by herbivore damage. The effect of diurnal versus nocturnal damage on the initiation of plant defense responses was investigated using MecWorm, a robotic device designed to reproduce tissue damage caused by herbivore attack. Lima bean leaves that were damaged by MecWorm during the photophase emitted maximal levels of beta-ocimene and (Z)-3-hexenyl acetate in the late photophase. Leaves damaged during the dark phase responded with the nocturnal emission of (Z)-3-hexenyl acetate, but with only low amounts of beta-ocimene; this emission was followed by an emission burst directly after the onset of light. In the presence of (13)CO(2), this light-dependent synthesis of beta-ocimene resulted in incorporation of 75% to 85% of (13)C, demonstrating that biosynthesis of beta-ocimene is almost exclusively fueled by the photosynthetic fixation of CO(2) along the plastidial 2-C-methyl-D-erythritol 4-P pathway. Jasmonic acid (JA) accumulated locally in direct response to the damage and led to immediate up-regulation of the P. lunatus beta-ocimene synthase gene (PlOS) independent of the phase, that is, light or dark. Nocturnal damage caused significantly higher concentrations of JA (approximately 2-3 times) along with enhanced expression levels of PlOS. Transgenic Arabidopsis thaliana transformed with PlOS promoter :: beta-glucuronidase fusion constructs confirmed expression of the enzyme at the wounded sites. In summary, damage-dependent JA levels directly control the expression level of PlOS, regardless of light or dark conditions, and photosynthesis is the major source for the early precursors of the 2-C-methyl-D-erythritol 4-P pathway.     

在伤信号传导中茉莉酸与水杨酸的关系

近年来,发现茉莉酸和水杨酸都是植物体对外界伤害作出反应,表达抗性基因的信号分子。水杨酸可抑制茉莉酸类的合成及其所诱导的蛋白基因的表达;茉莉酸能阻止病原侵染后所产生的水杨酸的增加。茉莉酸信号转导途径和水杨酸信号转导途径存在着交叉,小GTP结合蛋白和细胞分裂素可能起着信号开关的作用。     

12-hydroxyjasmonic acid glucoside is a COI1-JAZ-independent activator of leaf-closing movement in Samanea saman

Jasmonates are ubiquitously occurring plant growth regulators with high structural diversity that mediate numerous developmental processes and stress responses. We have recently identified 12-O-β-D-glucopyranosyljasmonic acid as the bioactive metabolite, leaf-closing factor (LCF), which induced nyctinastic leaf closure of Samanea saman. We demonstrate that leaf closure of isolated Samanea pinnae is induced upon stereospecific recognition of (-)-LCF, but not by its enantiomer, (+)-ent-LCF, and that the nonglucosylated derivative, (-)-12-hydroxyjasmonic acid also displays weak activity. Similarly, rapid and cell type-specific shrinkage of extensor motor cell protoplasts was selectively initiated upon treatment with (-)-LCF, whereas flexor motor cell protoplasts did not respond. In these bioassays related to leaf movement, all other jasmonates tested were inactive, including jasmonic acid (JA) and the potent derivates JA-isoleucine and coronatine. By contrast, (-)-LCF and (-)-12-hydroxyjasmonic acid were completely inactive with respect to activation of typical JA responses, such as induction of JA-responsive genes LOX2 and OPCL1 in Arabidopsis (Arabidopsis thaliana) or accumulation of plant volatile organic compounds in S. saman and lima bean (Phaseolus lunatus), generally considered to be mediated by JA-isoleucine in a COI1-dependent fashion. Furthermore, application of selective inhibitors indicated that leaf movement in S. saman is mediated by rapid potassium fluxes initiated by opening of potassium-permeable channels. Collectively, our data point to the existence of at least two separate JA signaling pathways in S. saman and that 12-O-β-D-glucopyranosyljasmonic acid exerts its leaf-closing activity through a mechanism independent of the COI1-JAZ module.     

Virulence systems of Pseudomonas syringae pv. tomato promote bacterial speck disease in tomato by targeting the jasmonate signaling pathway

Pseudomonas syringae pv. tomato strain DC3000 (Pst DC3000) causes bacterial speck disease on tomato. The pathogenicity of Pst DC3000 depends on both the type III secretion system that delivers virulence effector proteins into host cells and the phytotoxin coronatine (COR), which is thought to mimic the action of the plant hormone jasmonic acid (JA). We found that a JA-insensitive mutant (jai1) of tomato was unresponsive to COR and highly resistant to Pst DC3000, whereas host genotypes that are defective in JA biosynthesis were as susceptible to Pst DC3000 as wild-type (WT) plants. Treatment of WT plants with exogenous methyl-JA (MeJA) complemented the virulence defect of a bacterial mutant deficient in COR production, but not a mutant defective in the type III secretion system. Analysis of host gene expression using cDNA microarrays revealed that COR works through Jai1 to induce the massive expression of JA and wound response genes that have been implicated in defense against herbivores. Concomitant with the induction of JA and wound response genes, the type III secretion system and COR repressed the expression of pathogenesis-related (PR) genes in Pst DC3000-infected WT plants. Resistance of jai1 plants to Pst DC3000 was correlated with a high level of PR gene expression and reduced expression of JA/wound response genes. These results indicate that COR promotes bacterial virulence by activating the host's JA signaling pathway, and further suggest that the type III secretion system might also modify host defense by targeting the JA signaling pathway in susceptible tomato plants.     

植物的环境信号分子茉莉酸及其生物学功能

茉莉酸信号分子参与植物生长发育众多生理过程的调控,尤其是作为环境信号分子能有效地介导植物对生物及非生物胁迫的防御反应。迄今已知具有信号分子生理功能的至少包括茉莉酸(jasmonic acid,JA)以及茉莉酸甲酯(methyl jasmonate,Me JA)和茉莉酸-异亮氨酸复合物(jasmonoyl-isoleucine,JA-Ile)等茉莉酸衍生物,统称为茉莉酸类化合物(jasmonates,JAs)。从环境信号分子角度介绍了茉莉酸信号的启动(环境信号感知与转导、茉莉酸类化合物合成)、传递(局部传递、维管束传输、空气传播)和生物学功能(茉莉酸信号受体、调控的转录因子、参与的生物学过程)。     

Localized Wounding by Heat Initiates the Accumulation of Proteinase Inhibitor II in Abscisic Acid-Deficient Plants by Triggering Jasmonic Acid Biosynthesis

To test whether the response to electrical current and heat treatment is due to the same signaling pathway that mediates mechanical wounding, we analyzed the effect of electric-current application and localized burning on proteinase inhibitor II (Pin2) gene expression in both wild-type and abscisic acid (ABA)-deficient tomato (Lycopersicon esculentum Mill.) and potato (Solanum phureja) plants. Electric-current application and localized burning led to the accumulation of Pin2 mRNA in potato and tomato wild-type plants. Among the treatments tested, only localized burning of the leaves led to an accumulation of Pin2 mRNA in the ABA-deficient plants. Electric-current application, like mechanical injury, was able to initiate ABA and jasmonic acid (JA) accumulation in wild-type but not in ABA-deficient plants. In contrast, heat treatment led to an accumulation of JA in both wild-type and ABA-deficient plants. Inhibition of JA biosynthesis by aspirin blocked the heat-induced Pin2 gene expression in tomato wild-type leaves. These results suggest that electric current, similar to mechanical wounding, requires the presence of ABA to induce Pin2 gene expression. Conversely, burning of the leaves activates Pin2 gene expression by directly triggering the biosynthesis of JA by an alternative pathway that is independent of endogenous ABA levels.     

在伤信号传导中茉莉酸与水杨酸的关系

近年来,发现茉莉酸和水杨酸都是植物体对外界伤害作出反应,表达抗性基因的信号分子。水杨酸可抑制茉莉酸类的合成及其所诱导的蛋白基因的表达;茉莉酸能阻止病原侵染后所产缮乃钏岬脑黾印＼岳蛩嵝藕抛纪揪逗退钏嵝藕抛纪揪洞嬖谧沤徊妫。牵裕薪岷蛋白和细胞分裂素可能起着信号开关的作用。     

Jasmonate Signal Pathway in Arabidopsis

Jasmonates （JAs）, which include jasmonic acid and its cyclopentane derivatives are synthesized from the octadecanoid pathway and widely distributed throughout the plant kingdom. JAs modulate the expression of numerous genes and mediate responses to stress, wounding, insect attack, pathogen infection, and UV damage. They also affect a variety of processes in many plant developmental processes. The JA signal pathway involves two important events： the biosynthesis of JA and the transduction of JA signal. Several important Arabidopsis mutants in jasmonate signal pathway were described in this review.     

Induction of 12-oxo-phytodienoic acid in wounded plants and elicited plant cell cultures.

Jasmonic acid (JA) is rapidly biosynthesized from alpha-linolenic acid in plants upon contact with pathogens or wounding, and triggers gene activation, leading to the synthesis of defensive secondary metabolites and proteins. Despite the recent finding that its precursor, 12-oxo-phytodienoic acid (PDA), is a more powerful inducer of gene activation, interest has focused so far almost exclusively on JA. A validated negative chemical ionization-gas chromatography-mass spectrometry method has been developed that allows the simultaneous quantification of endogenous 12-oxo-PDA and JA in plant tissues. In six out of eight plant species tested maximal levels of 12-oxo-PDA exceeded peak levels of JA by approximately 3- to 5-fold after elicitation with a yeast cell wall preparation or when plants were wounded. These experiments support the hypothesis that 12-oxo-PDA acts as the predominant jasmonate signal in most plants, whereas JA remains an active metabolite of its precursor. Furthermore, JA but not 12-oxo-PDA was shown to be secreted into the medium from cultured plant cells, suggesting that JA may also act as an intercellular signal.     

Jasmonic acid in wound signal transduction pathways

Wounding induces expression of genes encoding defense-related proteins involved in wound healing. An intensive survey has been carried out to clarify the initial signal transduction pathways that mediate this stress to expression of genes. In this context, signal molecules that intermediate in the wound signal to cellular response have been actively searched for. Jasmonic acid (JA) has been considered to be a key signal molecule in this pathway. Systemin, ABA, ethylene, and electrical current have been suggested to function by transmitting the wound signal to JA. A mitogen-activated protein kinase has been shown to respond rapidly to wounding, and proposed to function as one of the key enzymes involved in JA biosynthesis. Transgenic plants overexpressing a gene encoding a Rab-type, small GTP-binding protein contained 6-fold higher levels of cytokinins than wild-type plants, and responded to wounding by rapidly producing JA and, uncommonly, accumulating salicylic acid (SA), a pathogenic signal. These phenomena observed in the transgenic plants were reproduced when wild-type plants were wounded in the presence of the synthetic cytokinin, benzylaminopurine, suggesting that cytokinins are indispensable in the control of endogenous levels of JA and SA.     

Aspirin prevents wound-induced gene expression in tomato leaves by blocking jasmonic acid biosynthesis

Jasmonic acid (JA) and its methyl ester, like mechanical wounding, strongly induce accumulation of proteinase inhibitor II (Pin2) in tomato and potato leaves. In plants, JA is synthesized from α-linolenic acid by a lipoxygenase (LOX)-mediated oxygenation leading to 13-hydroxyperoxylinolenic acid (13-HPLA) which is then subsequently transformed to JA by the action of hydroperoxide-dehydrase activity and additional modification steps. Both the chemical structure as well as the biosynthetic pathway of JA resemble those of the mammalian eicosanoids (prostaglandins and leukotrienes) which are derived from LOX-and cyclooxygenase (COX)-mediated reactions. To assess the role of endogenous JA in the wound response, detached tomato (Lycopersicon esculentum Mill.) leaves were supplied with different LOX and COX inhibitors and the expression of the wound-induced genes for Pin2 (Pin2), cathepsin D inhibitor (Cdi) and threonine deaminase (Td) was analyzed. Lipoxygenase inhibitors as well as some COX inhibitors blocked the wound-induced accumulation of Pin2, Cdi and Td mRNA. Quantitation of endogenous levels of JA showed that aspirin blocks the increase of this phytohormone normally observed as a result of wounding. Linolenic acid and 13-HPLA do not induce the expression of Pin2, Cdi and Td in the presence of aspirin. However, 12-oxo-phytodienoic acid and jasmonic acid are able to overcome the inhibitory effect of this substance. These results strongly indicate that aspirin prevents wound-induced gene activation by inhibiting the hydroxyperoxide-dehydrase activity that mediates the conversion of 13-HPLA to 12-oxo-phytodienoic acid.     

Abscisic acid and jasmonic acid activate wound-inducible genes in potato through separate, organ-specific signal transduction pathways

Mechanical damage to leaf tissue causes an increase in abscisic acid (ABA) which in turn activates the biosynthesis of jasmonic acid (JA). The resulting higher endogenous JA levels subsequently activate the expression of wound-inducible genes. This study shows that JA induces the expression of different sets of genes in roots and leaves of potato plants. When roots of intact plants were treated with JA, high levels of proteinase inhibitor II (pin2), cathepsin D inhibitor, leucine aminopeptidase and threonine deaminase mRNAs accumulated in the systemic leaves. However, in the treated roots, very low, if any, expression of these genes could be detected. In contrast, a novel, root-specific pin2 homologue accumulated in the JA-treated root tissue which could not be detected in leaves, either systemic or those directly treated with JA. Application of okadaic acid and staurosporine revealed that a protein phosphorylation step is involved in the regulation of this differential response. In leaves, a protein phosphatase is required for the JA-induced expression of pin2 and the other genes analysed. This phosphatase activity is not necessary for the JA-induced expression of a pin2 homologue in roots, suggesting the existence of different transduction pathways for the JA signal in these organs. The requirement of a protein phosphatase activity for JA-mediated gene induction has enabled identification of a JA-independent pathway for ABA induction of pin2 and the other wound-inducible genes. This alternative pathway involves a protein kinase, and appears to be selective for wound-inducible genes. Our data suggest the presence of a complex, organ-specific transduction network for regulating the effects of the plant hormones ABA and JA on gene expression upon wounding.