Functional characterization of wheat ent-kaurene(-like) synthases indicates continuing evolution of labdane-related diterpenoid metabolism in the cereals

Abstract

Wheat (Triticum aestivum) and rice (Oryza sativa) are two of the most agriculturally important cereal crop plants. Rice is known to produce numerous diterpenoid natural products that serve as phytoalexins and/or allelochemicals. Specifically, these are labdane-related diterpenoids, derived from a characteristic labdadienyl/copalyl diphosphate (CPP), whose biosynthetic relationship to gibberellin biosynthesis is evident from the relevant expanded and functionally diverse family of ent-kaurene synthase-like (KSL) genes found in rice the (OsKSLs). Herein reported is the biochemical characterization of a similarly expansive family of KSL from wheat (the TaKSLs). In particular, beyond ent-kaurene synthases (KS), wheat also contains several biochemically diversified KSLs. These react either with the ent-CPP intermediate common to gibberellin biosynthesis or with the normal stereoisomer of CPP that also is found in wheat (as demonstrated by the accompanying paper describing the wheat CPP synthases). Comparison with a barley (Hordeum vulgare) KS indicates conservation of monocot KS, with early and continued expansion and functional diversification of KSLs in at least the small grain cereals. In addition, some of the TaKSLs that utilize normal CPP also will react with syn-CPP, echoing previous findings with the OsKSL family, with such enzymatic promiscuity/elasticity providing insight into the continuing evolution of diterpenoid metabolism in the cereal crop plant family, as well as more generally, which is discussed here.