Elucidation of the genomic basis of indirect plant defense against insects.

Using airborne signals to attract herbivore predators and parasitoids is an important strategy that plants use in defense against herbivorous insects. The volatiles involved in this indirect plant defense are often chemically complex and variable across species. We recently established rice as a model for studying the molecular and genomic basis of volatile-mediated indirect plant defense. Rice plants when damaged by fall armyworm larvae become highly attractive to parasitic wasps. The volatiles potentially responsible for parasitoid attraction were determined to be a blend of compounds predominated by terpenoids, of which S-linalool is the most abundant. Racemic linalool alone was shown to be effective in attracting parasitic wasps. By combining volatile profiling and microarray analysis, a catalog of candidate genes for volatile biosynthesis was identified. Three genes encoding terpene synthases were biochemically characterized. They are responsible for the production of the majority of volatile terpenes released from insect-damaged rice plants. Additional candidate genes are being currently characterized for their role in production of other insect-induced volatiles from rice plants. Identification of a complete set of key genes for synthesizing herbivory-induced volatiles in rice will provide an important reference for comparative studies of this important defense trait across a variety of plant species.