Inferring Roles in Defense from Metabolic Allocation of Rice Diterpenoids.

Among their responses to microbial infection, plants deploy an arsenal of natural antibiotic products. Historically these have been identified on the basis of their antibiotic activity in vitro, which leaves open the question of their relevance to defense in planta. The vast majority of such natural products from the important crop plant rice () are diterpenoids whose biosynthesis proceeds via either - or -copalyl diphosphate (CPP) intermediates, which were isolated on the basis of their antibiotic activity against the fungal blast pathogen However, rice plants in which the gene for the -CPP synthase is knocked out do not exhibit increased susceptibility to Here, we show that knocking out or knocking down actually decreases susceptibility to the bacterial leaf blight pathogen By contrast, genetic manipulation of the gene for the -CPP synthase alters susceptibility to both and Despite the secretion of diterpenoids dependent on or from roots, neither knockout exhibited significant changes in the composition of their rhizosphere bacterial communities. Nevertheless, rice plants allocate substantial metabolic resources toward - as well as -CPP derived diterpenoids upon infection/induction. Further investigation revealed that plays a role in fungal non-host disease resistance. Thus, examination of metabolic allocation provides important clues into physiological function.