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      The products of a single maize sesquiterpene synthase form a volatile defense signal that attracts natural enemies of maize herbivores

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          Abstract

          Plants can defend themselves against herbivores by attracting natural enemies of the herbivores. The cues for attraction are often complex mixtures of herbivore-induced plant volatiles, making it difficult to demonstrate the role of specific compounds. After herbivory by lepidopteran larvae, maize releases a mixture of volatiles that is highly attractive to females of various parasitic wasp species. We identified the terpene synthase TPS10 that forms (E)-beta-farnesene, (E)-alpha-bergamotene, and other herbivory-induced sesquiterpene hydrocarbons from the substrate farnesyl diphosphate. The corresponding gene is expressed in response to herbivore attack and is regulated at the transcript level. Overexpression of tps10 in Arabidopsis thaliana resulted in plants emitting high quantities of TPS10 sesquiterpene products identical to those released by maize. Using these transgenic Arabidopsis plants as odor sources in olfactometer assays showed that females of the parasitoid Cotesia marginiventris learn to exploit the TPS10 sesquiterpenes to locate their lepidopteran hosts after prior exposure to these volatiles in association with hosts. This dissection of the herbivore-induced volatile blend demonstrates that a single gene such as tps10 can be sufficient to mediate the indirect defense of maize against herbivore attack.

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          Most cited references21

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          Defensive function of herbivore-induced plant volatile emissions in nature.

          Herbivore attack is known to increase the emission of volatiles, which attract predators to herbivore-damaged plants in the laboratory and agricultural systems. We quantified volatile emissions from Nicotiana attenuata plants growing in natural populations during attack by three species of leaf-feeding herbivores and mimicked the release of five commonly emitted volatiles individually. Three compounds (cis-3-hexen-1-ol, linalool, and cis-alpha-bergamotene) increased egg predation rates by a generalist predator; linalool and the complete blend decreased lepidopteran oviposition rates. As a consequence, a plant could reduce the number of herbivores by more than 90% by releasing volatiles. These results confirm that indirect defenses can operate in nature.
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            Isolation and identification of volatile kairomone that affects acarine predatorprey interactions Involvement of host plant in its production.

            A volatile kairomone emitted from lima bean plants (Phaseolus lunatus) infested with the spider miteTetranychus urticae, was collected on Tenax-TA and analyzed with GC-MS. Two components were identified as the methylene monoterpene (3E)-4,8-dimethyl-1,3,7-nonatriene and the methylene sesquiterpene (3E,7E)-4,8,12-dimethyl-1,3,7,11-tridecatetraene, respectively, after purification by preparative GC on a megabore column and recording of UV, IR, and [(1)H]NMR spectra. The response of two species of predatory mites towards the identified chemicals was tested in a Y-tube olfactometer. Four of the compounds tested, linalool (3,7-dimethyl-1,6-octadien-3-ol), (E)-β-ocimene [(3E)-3,7-dimethyl-1,3,6-octatriene], (3E)-4,8-dimethyI-1,3,7-nonatriene, and methyl salicylate attracted females ofPhytoseiulus persimilis. Linalool and methyl salicylate attracted females ofAmblyseius potentillae. The response ofA. potentillae to these two kairomone components was affected by the rearing diet of the predators in the same way as was reported for the response to the natural kairomone blend: when reared on a carotenoid-deficient diet, the predators responded to the volatile kairomone ofT. urticae, but when reared on a carotenoid-containing diet they did not. The identified kairomone components are all known from the plant kingdom. They are not known to be produced by animals de novo. In addition to biological evidence, this chemical evidence suggests that the plant is involved in production of the kairomone. Based on the present study and literature data on the response ofT. urticae to infochemicals, it is concluded that the kairomone component linalool is also a component of a volatile spider-mite dispersing pheromone.
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              Biosynthesis and emission of terpenoid volatiles from Arabidopsis flowers.

              Arabidopsis is believed to be mostly self-pollinated, although several lines of genetic and morphological evidence indicate that insect-mediated outcrossing occurs with at least a low frequency in wild populations. Here, we show that Arabidopsis flowers emit both monoterpenes and sesquiterpenes, potential olfactory cues for pollinating insects. Of the 32 terpene synthase genes in the Arabidopsis genome, 20 were found to be expressed in flowers, 6 of these exclusively or almost exclusively so. Two terpene synthase genes expressed exclusively in the flowers and one terpene synthase gene expressed almost exclusively in the flowers were characterized and found to encode proteins that catalyze the formation of major floral volatiles. A beta-glucuronidase fusion construct with a promoter of one of these genes demonstrated that gene expression was restricted to the sepals, stigmas, anther filaments, and receptacles, reaching a peak when the stigma was receptive to cross pollen. The observation that Arabidopsis flowers synthesize and emit volatiles raises intriguing questions about the reproductive behavior of Arabidopsis in the wild and allows detailed investigations of floral volatile biosynthesis and its regulation to be performed with this model plant system.
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                Author and article information

                Journal
                Proceedings of the National Academy of Sciences
                Proceedings of the National Academy of Sciences
                Proceedings of the National Academy of Sciences
                0027-8424
                1091-6490
                January 24 2006
                January 24 2006
                January 17 2006
                January 24 2006
                : 103
                : 4
                : 1129-1134
                Article
                10.1073/pnas.0508027103
                1347987
                16418295
                efc7a066-b681-4186-b283-5a0b8dc1e40a
                © 2006
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