Evolution of biosynthetic genes of diterpene-type phytoalexins in cultivated rice

Abstract

Cultivated rice （Oryza sativa） produces various diterpenoid phytoalexins for defense, including phytocassanes, momilactones and oryzalexins. Carbon skeletons of the diterpenoid phytoalexins are biosynthesized from geranylgeranyl diphosphate via ent-copalyl diphosphate or syn-copalyl diphosphate, and the phytoalexins are generated by chemical modification of each carbon skeleton.　We identified diterpene cyclase genes that are responsible for forming the carbon skeletons of the phytoalexins: OsCPS2, CPS4, KSL4, KSL7, KSL8 and KSL10.　Other biosynthetic genes involved in the modification of the carbon skeletons, including cytochrome P450 （CYP） genes, have been identified, suggesting the existence of biosynthetic gene clusters for phytocassanes and momilactones.　In this review, we introduce the rice diterpenoid phytoalexin biosynthetic genes identified so far, and propose their possible evolutionary history.