Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 2004
Publication Date: December 1, 2004
Citation: Lawrence, S.D., Novak, N.G. 2004. Maize genes induced by herbivory and volicitin. Journal of Chemical Ecology.30(12) 2543-2557. Interpretive Summary: Currently available insect resistant transgenic (genetically engineered) plants produce large amounts of insect toxin throughout the life of the plant. This is a problem because continuous toxin production places a burden on the plant that could reduce crop productivity. We are attempting to produce a new generation of transgenic plants that make toxin only when the insect feeds. To begin this process, we have looked for plant genes that are turned on specifically by insect attack. We have found one gene whose product is present only after insect feeding, although it is also made to a lesser extent upon wounding of the plant. Researchers can use this gene in a program to improve genetically engineered insect resistant plants.
Technical Abstract: In crop plants, mechanical damage and insect attack trigger rapid changes in gene transcription. Does insect herbivory differ from a general wound response? If so, is this induction specific to the pest/host plant interaction? Herbivory by beet armyworm (BAW) caterpillars on maize results in a unique pattern of volatile compounds not triggered by wounding alone. This bouquet of volatiles attracts the generalist parasitoid, Cotesia marginiventris and enables natural enemies to locate the offending caterpillars. Caterpillar induced volatile emission can be mimicked when volicitin, a component of the BAW oral secretions, is added to a wounded leaf. We have identified genes that are affected by BAW feeding by comparing volicitin treatment with wounding alone. We compared cDNAs from these two populations by isolating genes from a subtractive library and using reverse northerns. Virtual northern blots confirmed these results and further showed that BAW infestation affected the expression of these genes. In some cases BAW feeding actually inhibited the expression of volicitin-induced genes. We have found that transcripts involved in volatile production are increased by volicitin treatment and BAW infestation, and are present in lesser amounts in the mechanically wounded leaves. Finally, three new sesquiterpene cyclase genes that are induced by volicitin have been identified.