Cytochrome P450 CYP79B2 from Arabidopsis Catalyzes the Conversion of Tryptophan to Indole-3-acetaldoxime, a Precursor of Indole Glucosinolates and Indole-3-acetic Acid

Glucosinolates are natural plant products known as flavor compounds, cancer-preventing agents, and biopesticides. We report cloning and characterization of the cytochrome P450 CYP79B2 fromArabidopsis. Heterologous expression of CYP79B2 inEscherichia coli shows that CYP79B2 catalyzes the conversion of tryptophan to indole-3-acetaldoxime. Recombinant CYP79B2 has a Km of 21 μm and aVmax of 7.78 nmol/h/ml culture. Inhibitor studies show that CYP79B2 is different from a previously described enzyme activity that converts tryptophan to indole-3-acetaldoxime (Ludwig-Müller, J., and Hilgenberg, W. (1990)Phytochemistry, 29, 1397–1400). CYP79B2 is wound-inducible and expressed in leaves, stem, flowers, and roots, with the highest expression in roots. Arabidopsis overexpressing CYP79B2 has increased levels of indole glucosinolates, which strongly indicates that CYP79B2 is involved in indole glucosinolate biosynthesis. Our data show that oxime production by CYP79s is not restricted to those amino acids that are precursors for cyanogenic glucosides. Our data are consistent with the hypothesis that indole glucosinolates have evolved from cyanogenesis. Indole-3-acetaldoxime is a precursor of the plant hormone indole-3-acetic acid, which suggests that CYP79B2 might function in biosynthesis of indole-3-acetic acid. Identification of CYP79B2 provides an important tool for modification of the indole glucosinolate content to improve nutritional value and pest resistance.