A role for flavin monooxygenase-like enzymes in auxin biosynthesis

Although auxin is known to regulate many processes in plant development and has been studied for over a century, the mechanisms whereby plants produce it have remained elusive. Here we report the characterization of a dominan t Arabidopsis mutant,yucca, which contains elevated Levels of free auxin. Y UCCA encodes a flavin monooxygenase-like enzyme and belongs to a family tha t includes at Least nine other homologous Arabidopsis genes, a subset of wh ich appears to have redundant functions, Results from tryptophan analog fee ding experiments and biochemical assays indicate that YUCCA catalyzes hydro xylation of the amino group of tryptamine, a rate-limiting step in tryptoph an-dependent auxin biosynthesis.