Investigating labdane-related diterpenoids biosynthetic network in rice: Characterization of cytochromes P450 and short-chain alcohol dehydrogenases/reductase

Terpenoids are a family of natural occurring compounds with various physiological functions in organisms. They serve as hormone, phytoalexins, and pharmaceuticals. Elucidating biosynthetic pathway of terpenoids is key to understand and utilize terpenoids. Terpene cyclases are crucial enzymes that are responsible for the biosynthesis of terpene backbones and hence have been intensively studied. However, the downstream elaborations are poorly understood, in which terpenoids are transformed with bioactivity. In this dissertation, I used rice as a model system to investigate the oxidation steps of labdane-related diterpenoids phytoalexins. Taken the advantage that there are two hypothetic LRD biosynthetic gene clusters in rice, we biochemically characterized two CYPs in initial oxidation steps of LRD biosynthesis by screening corresponding CYP from LRD gene cluster. Furthermore, CYPs and SDRs catalyzing hydroxylation and oxidation reactions in the biosynthesis of oryzalexin A - E were characterized. Our results have identified enzymes involved in the rice oryzalexin biosynthesis and hence established the first complete LRD biosynthesis network in rice and probably many other plant species.