Efficient Conversion of L-Tryptophan to Indole-3-Acetic Acid and/or Tryptophol by Some Species of Rhizoctonia

In a study of various phytopathogenic fungi, we found that fungi that belong to the genus Rhizoctonia produce IAA efficiently from tryptophan. R. solani Kiihn MAFF-305219, in particular, produced large amounts of tryp-tophol (Tol), which was assumed to be a specific by-pro-duct of the indole-3-pyruvate (IPy) pathway, in addition to IAA. Therefore, this fungus seemed suitable for analysis of the function and the regulation of the biosynthesis of auxin by a fungal pathogen. Under normal aerobic conditions, the ratio of IAA to Tol synthesized by this strain was higher than that under less aerobic conditions. In metabol-ic studies with various indole derivatives, R. solani con-verted L-tryptophan and indole-3-acetaldehyde to IAA and Tol, but other indole derivatives were scarcely metabo-lized. These results suggest that both IAA and Tol are syn-thesized from tryptophan through the IPy pathway in