An herbivore elicitor activates the gene for indole emission in maize

Maize and a variety of other plant species release volatile compounds in re sponse to herbivore attack that serve as chemical cues to signal natural en emies of the feeding herbivore. N-(17-hydroxy-linolenoyl)-L-glutamine is an elicitor component that has been isolated and chemically characterized fro m the regurgitant of the herbivore-pest beet armyworm. This fatty acid deri vative, referred to as volicitin, triggers the synthesis and release of Vol atile components, including terpenoids and indole in maize. Here we report on a previously unidentified enzyme, indole-3-glycerol phosphate lyase (IGL ), that catalyzes the formation of free indole and is selectively activated by volicitin. IGL's enzymatic properties are similar to BX1, a maize enzym e that serves as the entry point to the secondary defense metabolites DIBOA and DIMBOA. Gene-sequence analysis indicates that Igl and Bx1 are evolutio narily related to the tryptophan synthase alpha subunit.