Inferring roles in defense from metabolic allocation of rice diterpenoids

Among their responses to microbial infection, plants deploy an arsenal of antibiotic natural products. While these historically have been identified on the basis of their antibiotic activity in vitro, this leaves open the question of their relevance to defense in planta. The vast majority of such natural products from the important crop plant rice (Oryza sativa) are diterpenoids whose biosynthesis proceeds via either ent- or syncopalyl diphosphate (CPP) intermediates, and which were isolated on the basis of their antibiotic activity against the fungal blast pathogen Magnaporthe oryzae. However, rice plants in which the gene for the syn-CPP synthase Os-CPS4 is knocked-out do not exhibit increased susceptibility to M. oryzae. Here it is further shown that knocking-out or knocking-down Os-CPS4 actually decreases susceptibility to the bacterial leaf blight pathogen Xanthomonas oryzae. On the other hand, knocking-out or knocking-down the gene for the ent-CPP synthase Os-CPS2 is found to incr...