Studies on functional analysis of cytochrome P450s in the biosynthetic pathway of terpenoid phytohormones

Abstract

Since the 1990s, genetic studies aimed at analyzing causal genes from mutants have been actively conducted, leading to the rapid elucidation of the biosynthesis and signaling pathways of phytohormones. My research has focused on analyzing mutants associated with the terpenoid phytohormones, brassinosteroids (BR), gibberellins (GA), and strigolactones (SL). In particular, I have elucidated the functions of cytochrome P450 enzymes, a type of oxidases that are encoded as the causal genes of the following mutants. In the BR studies, the analysis of the dwarf tomato mutant d^x resulted in the discovery of CYP85A3, which catalyzes the conversion of castasterone to brassinolide, representing the final step in the BR biosynthetic pathway. In the GA studies, CYP714D1, encoded by the causal gene for the tall rice mutant eui, was identified as a novel deactivation enzyme responsible for 16α,17-epoxidation of GAs. Additionally, I found that a C-13 oxidase in the GA₁ biosynthetic pathway is also encoded by CYP714. Concerning the SL studies, CYP711A1, encoded by the causal gene for the highly branching mutant max1 in Arabidopsis, was identified as the enzyme catalyzing the conversion of the SL precursor carlactone to carlactonoic acid. Furthermore, I investigated the function of CYP711As in various plant species and found that the biosynthetic pathways following carlactonoic acid are diverse among plant species.