Abstract
Brassinosteroids (BRs) are plant steroid hormones that are essential for normal plant growth and development. Cytochrome P450 monooxygenases (P450s) play crucial roles in BR biosynthesis from campesterol to brassinolide. Recent molecular genetic studies for BR-deficient mutants of Arabidopsis, rice, tomato and garden pea have identified several P450 genes (CYP85A, 90A, 90B, 90C, 90D, and 724B) so far. Recently, we have characterized Arabidopsis CYP90C1 and CYP90D1 functionally expressed in insect cells and found that CYP90C1 and CYP90D1 are redundant C-23 hydroxylases. Here, we report biochemical characterization of a P450, C-3 oxidase. The P450 was expressed in insect cells using a baculovirus expression system. The P450 activity was measured in an in vitro assay and the reaction products were analyzed by GC-MS. These results indicated that the P450 is BR C-3 oxidase. To our knowledge, this is the first report of the biochemical characterization of the C-3 oxidation by the P450.
