Rice contains two disparate ent-copalyl diphosphate synthases with distinct metabolic functions

Rice (Oryza saliva) produces ent-copalyl diphosphate for both gibberellin (GA) phytohormone and defensive phytoalexin biosynthesis, raising the question of how this initial biosynthetic step is carried out for these distinct metabolic processes. Here, a functional genomics approach has been utilized to identify two disparate ent-copalyl diphosphate synthases from rice (OsCPS1(ent) and OsCPS2(ent)). Notably, it was very recently demonstrated that only one of these (OsCPS1(ent)) normally operates in GA biosynthesis as mutations in this gene result in severely impaired growth. Evidence is presented here strongly indicating that the other (OsCPS2(ent)) is involved in related secondary metabolism producing defensive phytochemicals. In particular, under appropriate conditions, OsCPS2(ent) mRNA is specifically induced in leaves prior to production of the corresponding phytoalexins. Thus, transcriptional control of OsCPS2(ent) seems to be an important means of regulating defensive phytochemical biosynthesis. Finally, OsCPS1(ent) is significantly more similar to the likewise GA-specific gene An1/ZmCPS1(ent) in maize (Zea mays) than its class II terpene synthase paralogs involved in rice secondary metabolism. Hence, we speculate that this cross-species conservation by biosynthetic process reflects derivation of related secondary metabolism from the GA primary biosynthetic pathway prior to the early divergence between the separate lineages within the cereal/grass family (Poaceae) resulting in modern rice and maize.