jasmonic-acid and beta-ocimene

Huanglongbing (HLB), spread by the Asian citrus psyllid (ACP), is a widespread, devastating disease that causes significant losses in citrus production. Therefore, controlling the ACP infestation and HLB infection is very important for citrus production. The aim of our study was to identify any citrus volatile which could be used as a repellent or less attractant towards ACP, and to envisage the potential of this strategy to control HLB spread. The present study identified a terpene synthase (TPS)-encoding gene CsTPS21 in citrus plants, and this gene was predicted to encode a monoterpene synthase and had an amino acid sequence similar to β-ocimene synthase. CsTPS21 was significantly upregulated by ACP infestation and methyl jasmonic acid (MeJA) treatment but downregulated by salicylic acid (SA). Further heterologous gene expression studies in yeast cells and tobacco plants indicated that the protein catalyzed the formation of β-ocimene, which acted as an ACP repellent. Detailed analysis of tobacco overexpressing CsTPS21 showed that CsTPS21 synthesizing β-ocimene regulated jasmonic acid (JA)-associated pathways by increasing the JA accumulation and inducing the JA biosynthetic gene expression to defend against insect infestation. These findings provide a basis to plan strategies to manage HLB in the field using β-ocimene and CsTPS21 as candidates.

Topics: Animals; Citrus; Hemiptera; Plant Diseases

Herbivore-induced plant volatiles (HIPVs) act as direct defenses against herbivores and as indirect defenses by attracting herbivore enemies. However, the involvement of HIPVs in within-plant or plant-to-plant signaling is not fully clarified. Furthermore, in contrast to model plants, HIPV signaling roles in crops have hardly been reported. Here, we investigated HIPVs emitted from tea (Camellia sinensis) plants, an important crop used for beverages, and their involvement in tea plant-to-plant signaling. To ensure uniform and sufficient exposure to HIPVs, jasmonic acid combined with mechanical damage (JAMD) was used to simulate herbivore attacks. Metabonomics techniques based on ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry and gas chromatography-mass spectrometry were employed to determine metabolite changes in undamaged tea plants exposed to JAMD-stimulated volatiles. JAMD-stimulated volatiles mainly enhanced the amounts of 1-O-galloyl-6-O-luteoyl-α-d-glucose, assamicain C, 2,3,4,5-tetrahydroxy-6-oxohexyl gallate, quercetagitrin, 2-(2-(3,4-dihydroxyphenyl)-5,7-dihydroxy-4-oxo-4H-chromen-8-yl)-4,5-dihydroxy-6-(hydroxymethyl)-tetrahydro-2H-pyran-3-yl, 3,4-dimethoxybenzoate, 1,3,4,5,6,7-hexahydroxyheptan-2-one, and methyl gallate in neighboring undamaged tea leaves. Furthermore, α-farnesene and β-ocimene, which were produced after JAMD treatments, were identified as two main JAMD-stimulated volatiles altering metabolite profiles of the neighboring undamaged tea leaves. This research advances our understanding of the ecological functions of HIPVs and can be used to develop crop biological control agents against pest insects in the future.

Topics: Acyclic Monoterpenes; Alkenes; Animals; Camellia sinensis; Cyclopentanes; Herbivory; Insecta; Oxylipins; Pest Control, Biological; Plant Growth Regulators; Sesquiterpenes; Signal Transduction; Volatile Organic Compounds

Attack by multiple herbivores often leads to modification of induced plant defenses compared to single herbivory, yet little is known about the effects on induced indirect plant defense. Here, we investigated the effect of sequential induction of plant defense by Mamestra brassicae caterpillar oral secretion and an infestation by Tetranychus urticae spider mites on the expression of indirect plant defense in Lima bean plants. The effect on indirect defense was assessed using behavior assays with the specialist predatory mite Phytoseiulus persimilis in an olfactometer, headspace analysis of 11 major herbivore-induced plant volatiles (HIPVs) including (E)-β-ocimene, and transcript levels of the corresponding gene Phaseolus lunatus (E)-β-ocimene synthase (PlOS). Predatory mites were found to distinguish between plants induced by spider mites and caterpillar oral secretion but not between plants with single spider mite infestation and plants induced by caterpillar oral secretion prior to spider mite infestation. Indeed, the volatile blends emitted by plants induced by spider mites only and the sequential induction treatment of caterpillar oral secretion followed by spider mite infestation, were similar. Our results suggest that plant indirect defense is not affected by previous treatment with oral secretion of M. brassicae caterpillars.

Topics: Acari; Acyclic Monoterpenes; Alkenes; Animals; Chemotaxis; Cyclopentanes; Female; Gene Expression Regulation; Herbivory; Larva; Moths; Oxylipins; Phaseolus; Pheromones; Plant Proteins; Predatory Behavior; Tetranychidae

Jasmonic acid (JA) plays a central role in induced plant defence e.g. by regulating the biosynthesis of herbivore-induced plant volatiles that mediate the attraction of natural enemies of herbivores. Moreover, exogenous application of JA can be used to elicit plant defence responses similar to those induced by biting-chewing herbivores and mites that pierce cells and consume their contents. In the present study, we used Lima bean (Phaseolus lunatus) plants to explore how application of a low dose of JA followed by minor herbivory by spider mites (Tetranychus urticae) affects transcript levels of P. lunatus (E)-β-ocimene synthase (PlOS), emission of (E)-β-ocimene and nine other plant volatiles commonly associated with herbivory. Furthermore, we investigated the plant's phytohormonal response. Application of a low dose of JA increased PlOS transcript levels in a synergistic manner when followed by minor herbivory for both simultaneous and sequential infestation. Emission of (E)-β-ocimene was also increased, and only JA, but not SA, levels were affected by treatments. Projection to latent structures-discriminant analysis (PLS-DA) of other volatiles showed overlap between treatments. Thus, a low-dose JA application results in a synergistic effect on gene transcription and an increased emission of a volatile compound involved in indirect defence after herbivore infestation.

Topics: Acyclic Monoterpenes; Alkenes; Animals; Cyclopentanes; Dose-Response Relationship, Drug; Gene Expression Regulation, Plant; Herbivory; Intramolecular Lyases; Oxylipins; Phaseolus; Plant Growth Regulators; Plant Proteins; Polymerase Chain Reaction; Terpenes; Tetranychidae

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.

Topics: Acetates; Acyclic Monoterpenes; Alkenes; Animals; Carbon Isotopes; Circadian Rhythm; Cyclopentanes; Erythritol; Gene Expression Regulation, Plant; Host-Parasite Interactions; Larva; Light; Molecular Sequence Data; Oxylipins; Phaseolus; Plant Leaves; Plant Proteins; Signal Transduction; Spodoptera; Sugar Phosphates; Up-Regulation; Volatilization

(E)-beta-Ocimene is one of the most commonly found monoterpenes of the volatile blends that are emitted from leaves in response to damage by herbivores or mechanical wounding. (E)-beta-Ocimene is also a component of many floral scents. Airborne (E)-beta-ocimene emitted from plants can serve as a chemical cue for the attraction of parasitoids or predators of plant herbivores and also as an attractant for pollinating insects. Furthermore, exposure of plants to (E)-beta-ocimene can activate defense gene expression. In this paper, we describe cDNA cloning and functional characterization of a gene encoding a highly specialized (E)-beta-ocimene synthase, AtTPS03, from Arabidopsis thaliana (L.) Heynh. AtTPS03 was identified as a member of the large AtTPS gene family of putative terpene synthases. A cDNA for AtTPS03 was expressed in Escherichia coli and the enzyme function identified in vitro. The A. thaliana (E)-beta-ocimene synthase produces almost exclusively (E)-beta-ocimene (94%) with minor amounts of the related acyclic monoterpenes (Z)-beta-ocimene (4%) and myrcene (2%). Transcripts for AtTPS03 were up-regulated in leaves of Arabidopsis in response to mechanical wounding and treatment with jasmonic acid, concurrent with induced emission of (E)-beta-ocimene. AtTPS03 provides an important gene for probing plant-insect and possibly plant-plant interactions mediated by terpenoid volatiles.

Topics: Acyclic Monoterpenes; Alkenes; Amino Acid Sequence; Arabidopsis; Arabidopsis Proteins; Cloning, Molecular; Cyclopentanes; DNA, Complementary; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Intramolecular Lyases; Molecular Sequence Data; Monoterpenes; Oxylipins; Sequence Analysis, DNA; Sequence Homology, Amino Acid; Stress, Mechanical; Volatilization

We report the synergistic effects of exogenous 1-aminocyclopropane-1-carboxylic acid (ACC) and jasmonic acid (JA) on production of induced volatiles by excised lima bean leaves. Application of ACC alone to leaves induced trace amounts of volatiles. ACC positively affected three JA-induced volatiles, (E)- and (Z)-beta-ocimene, and (Z)-3-hexenyl acetate. The ethylene inhibitor, silver thiosulfate, inhibited the production of these compounds. The results suggest synergistic effects of JA and ACC on inducible volatile production by lima bean leaves. Furthermore, lima bean leaves treated with JA plus ACC became more attractive to predatory mites, Phytoseiulus persimilis, than those treated with JA alone.

Topics: Acari; Acetates; Acyclic Monoterpenes; Alkenes; Amino Acids, Cyclic; Animals; Cyclopentanes; Mite Infestations; Oxylipins; Phaseolus; Plant Leaves; Volatilization