Jasmonate-dependent plant defense restricts thrips performance and preference

<p>Abstract</p> <p>Background</p> <p>The western flower thrips (<it>Frankliniella occidentalis </it>[Pergande]) is one of the most important insect herbivores of cultivated plants. However, no pesticide provides complete control of this species, and insecticide resistance has emerged around the world. We previously reported the important role of jasmonate (JA) in the plant's immediate response to thrips feeding by using an <it>Arabidopsis </it>leaf disc system. In this study, as the first step toward practical use of JA in thrips control, we analyzed the effect of JA-regulated <it>Arabidopsis </it>defense at the whole plant level on thrips behavior and life cycle at the population level over an extended period. We also studied the effectiveness of JA-regulated plant defense on thrips damage in Chinese cabbage (<it>Brassica rapa </it>subsp. <it>pekinensis</it>).</p> <p>Results</p> <p>Thrips oviposited more on <it>Arabidopsis </it>JA-insensitive <it>coi1-1 </it>mutants than on WT plants, and the population density of the following thrips generation increased on <it>coi1-1 </it>mutants. Moreover, thrips preferred <it>coi1-1 </it>mutants more than WT plants. Application of JA to WT plants before thrips attack decreased the thrips population. To analyze these important functions of JA in a brassica crop plant, we analyzed the expression of marker genes for JA response in <it>B. rapa</it>. Thrips feeding induced expression of these marker genes and significantly increased the JA content in <it>B. rapa</it>. Application of JA to <it>B. rapa </it>enhanced plant resistance to thrips, restricted oviposition, and reduced the population density of the following generation.</p> <p>Conclusion</p> <p>Our results indicate that the JA-regulated plant defense restricts thrips performance and preference, and plays an important role in the resistance of <it>Arabidopsis </it>and <it>B. rapa </it>to thrips damage.</p

Herbivore-Specific, Density-Dependent Induction of Plant Volatiles: Honest or “Cry Wolf” Signals?

Plants release volatile chemicals upon attack by herbivorous arthropods. They do so commonly in a dose-dependent manner: the more herbivores, the more volatiles released. The volatiles attract predatory arthropods and the amount determines the probability of predator response. We show that seedlings of a cabbage variety (Brassica oleracea var. capitata, cv Shikidori) also show such a response to the density of cabbage white (Pieris rapae) larvae and attract more (naive) parasitoids (Cotesia glomerata) when there are more herbivores on the plant. However, when attacked by diamondback moth (Plutella xylostella) larvae, seedlings of the same variety (cv Shikidori) release volatiles, the total amount of which is high and constant and thus independent of caterpillar density, and naive parasitoids (Cotesia vestalis) of diamondback moth larvae fail to discriminate herbivore-rich from herbivore-poor plants. In contrast, seedlings of another cabbage variety of B. oleracea (var. acephala: kale) respond in a dose-dependent manner to the density of diamondback moth larvae and attract more parasitoids when there are more herbivores. Assuming these responses of the cabbage cultivars reflect behaviour of at least some genotypes of wild plants, we provide arguments why the behaviour of kale (B. oleracea var acephala) is best interpreted as an honest signaling strategy and that of cabbage cv Shikidori (B. oleracea var capitata) as a “cry wolf” signaling strategy, implying a conflict of interest between the plant and the enemies of its herbivores: the plant profits from being visited by the herbivore's enemies, but the latter would be better off by visiting other plants with more herbivores. If so, evolutionary theory on alarm signaling predicts consequences of major interest to students of plant protection, tritrophic systems and communication alike

Volatile compounds from young peach shoots attract males of oriental fruit moth in the field

The oriental fruit moth (OFM) is one of the most serious pests of commercial fruit orchards worldwide. Newly planted peach trees in particular, can be very attractive for mated OFM females for oviposition. Samples of airborne host plant volatiles from intact young peach shoot tips and old leaves of the same potted plants were collected and analyzed with a gas chromatograph-mass spectrometer. Chemicals present in young shoot tips, but not in old leaves, were used for field trials. Moth capture by traps with the synthetic chemicals was compared to that of the standard terpinyl acetate (TA) food trap. The TA food trap caught OFM males and mated females, but tested synthetic chemicals trapped only OFM males. We observed that the mixture of (Z)-3-hexenyl acetate: (E)-β-ocimene: (E)-β-farnesene in proportion 1:2:2 attracted OFM males. Further, 1 mg of (E)-β-ocimene, and that of (E)-β-farnesene also attracted OFM males

Herbivore-Induced Defense Response in a Model Legume. Two-Spotted Spider Mites Induce Emission of (E)-β-Ocimene and Transcript Accumulation of (E)-β-Ocimene Synthase in Lotus japonicus

Indirect defense of plants against herbivores often involves the induced emission of volatile infochemicals including terpenoids that attract natural enemies of the herbivores. We report the isolation and characterization of a terpene synthase cDNA (LjEβOS) from a model legume, Lotus japonicus. Recombinant LjEβOS enzyme produced (E)-β-ocimene (98%) and its Z-isomer (2%). Transcripts of LjEβOS were induced in L. japonicus plants infested with two-spotted spider mites (Tetranychus urticae), coinciding with increasing emissions of (E)-β-ocimene as well as other volatiles, (Z)-3-hexenyl acetate and (E)-4,8-dimethyl-1,3,7-nonatriene, by the infested plants. We suggest that LjEβOS is involved in the herbivore-induced indirect defense response of spider mite-infested L. japonicus via de novo formation and emission (E)-β-ocimene. Mechanical wounding of the leaves or application of alamethicin (ALA), a potent fungal elicitor of plant volatile emission, also induced transiently increased levels of LjEβOS transcripts in L. japonicus. However, wounding or ALA did not result in elevated release of (E)-β-ocimene. Differences in volatile emissions after herbivory, mechanical wounding, or treatment with ALA suggest that neither a single mechanical wounding event nor ALA simulate the effect of herbivore activity and indicate that herbivore-induced emission of (E)-β-ocimene in L. japonicus involves control mechanisms in addition to up-regulation of LjEβOS transcripts

Disease severity enhancement by an esterase from non-phytopathogenic yeast Pseudozyma antarctica and its potential as adjuvant for biocontrol agents

Abstract The phylloplane yeast Pseudozyma antarctica secretes an esterase, named PaE, and xylanase when cultivated with xylose. We previously observed that the lipophilic layer of Micro-Tom tomato leaves became thinner after the culture filtrate treatment. The leaves developed reduced water-holding ability and became wilted. In this study, the purified enzymes were spotted on Micro-Tom leaves. PaE, but not xylanase, thinned the lipophilic layer of leaves and decreased leaf resistance to the phytopathogenic fungus Botrytis cinerea. Disease severity increased significantly in detached leaves and potted plants treated with the culture filtrate and B. cinerea spores compared with those treated with inactivated enzyme and B. cinerea alone. Spore germination ratios, numbers of penetrating fungal hyphae in the leaves, and fungal DNA contents also increased significantly on the detached leaves. Japanese knotweed (Fallopia japonica), a serious invasive alien weed in Europe and North America, also became susceptible to infection by the rust pathogen Puccinia polygoni-amphibii var. tovariae following the culture filtrate treatment. The culture filtrate treatment increased disease development in plants induced by both phytopathogenic fungi. Our results suggest that P. antarctica culture filtrate could be used as an adjuvant for sustainable biological weed control using phytopathogenic fungi