The CYP88A cytochrome P450, ent-kaurenoic acid oxidase, catalyzes three steps of the gibberellin biosynthesis pathway

We have shown that ent-kaurenoic acid oxidase, a member of the CYP88A subfa mily of cytochrome P450 enzymes, catalyzes the three steps of the gibberell in biosynthetic pathway from entkaurenoic acid to GA(12). A gibberellin-res ponsive barley mutant, grd5 accumulates ent-kaurenoic acid in developing gr ains. Three independent grd5 mutants contain mutations in a gene encoding a member of the CYP88A subfamily of cytochrome P450 enzymes, defined by the maize Dwarf3 protein. Mutation of the Dwarf3 gene gives rise to a gibberell in-responsive dwarf phenotype, but the lesion in the gibberellin biosynthes is pathway has not been identified. Arabidopsis thaliana has two CYP88A gen es, both of which are expressed. Yeast strains expressing cDNAs encoding ea ch of the two Arabidopsis and the barley CYP88A enzymes catalyze the three steps of the GA biosynthesis pathway from ent-kaurenoic acid to CA(12). Seq uence comparison suggests that the maize Dwarf3 locus also encodes ent-kaur enoic acid oxidase.