Cytochrome P450s in plant steroid hormone synthesis and metabolism

Cytochrome P450s (P450s) are essential for both plant steroid hormone biosynthesis and inactivation. Synthesis of plant steroid hormones, brassinosteroids (BRs), requires P450s of the CYP85 clan. This includes members of the CYP85, CYP90 and CYP724B families of P450s. These enzymes are associated with the hydroxylation/oxidation of the C-2, C-3, C-6, C-22 and C-23 positions with their function being determined via genetic and biochemical approaches. P450s involved in BR metabolism belong to the CYP72C and CYP734A families in the CYP72 clan of P450s. The CYP734A family is associated with C-26 hydroxylation of BRs. The transcriptional regulation of these genes via feedback regulation provides a mechanism for the maintenance of optimum BR levels. Phylogenetic analysis of these P450s highlights that the biosynthesis and metabolism genes have evolved independently. Similar analysis suggests that the Baeyer-Villiger reaction catalysed by the CYP85 family of P450s may have evolved independently in several dicotyledonous species. © 2006 Springer Science+Business Media B.V.