Occurrence, biosynthesis, and putative role of ecdysteroids in plants

Plants and insects over the course of time have developed a co- evolutionary arms race for survival. In plants the biosynthesis of the ecdysteroids, which have a known site of action in insects, provides a structure-function basis for phytoecdysteroid use as putative regulatory agents to alter insect predation. This putative regulation could be either immediate, halted feeding, or long-term, reduced fecundity or fitness of the insect herbivores. Proof of this hypothesis will ultimately require the availability of variants of a plant species that do not biosynthesize ecdysteroids as well as those that do biosynthesize ecdysteroids. The recent developments in our fundamental understanding of the biochemistry, regulation, and transport of ecdysteroids in plants provides a starting point for the experimental design of the requisite investigations. The physiological distribution and apparent cycling of ecdysteroids within perennial plants would likely limit hypotheses testing to genetically modified annuals. Unfortunately, Arabidopsis thaliana does not biosynthesize any detectable nonconjugated phytoecdysteroids (Grebenok and Adler, unpublished). Thus, analysis would likely require a different host species. Several potential sites for controlled alteration of phytoecdysteroid biosynthesis are becoming more evident as our fundamental knowledge of the ecdysteroid pathway is elucidated.