Identification of a cytochrome P450 gene that encodes steviol synthase in Arabidopsis

Abstract

In the course of experiments to search for enzymes involved in phytohormone metabolism, we found a new cytochrome P450 monooxygenase (P450) that is involved in gibberellin (GA) metabolism in Arabidopsis. Using a yeast expression system, we found that this P450 enzyme catalyzed the conversion of ent-kaurenoic acid into steviol (ent-13-hydroxykaurenoic acid). When GA₁₂ was used as the substrate, 12α-hydroxy GA₁₂ was produced as a major metabolite and 13-hydroxy GA₁₂ (GA₅₃) was detected as a minor product. Transgenic Arabidopsis plants overexpressing this P450 gene showed semi-dwarfism like mild GA-deficient mutants. GA analysis indicated that the levels of non 13-hydroxy GAs including GA₄ were decreased, whereas those of 13-hydroxy GAs including GA₁ (which is less active in Arabidopsis) were increased in the transgenic plants. These results demonstrate that the ratio of GA₄ to GA₁ in plants can be modified using this gene.