The Arabidopsis YUCCA1 Flavin Monooxygenase Functions in the Indole-3-Pyruvic Acid Branch of Auxin Biosynthesis

• Published in: The Plant cell 2011-11, Vol.23 (11), p.3961-3973
• Main Authors: Stepanova, Anna N., Yun, Jeonga, Robles, Linda M., Novak, Ondrej, He, Wenrong, Guo, Hongwei, Ljung, Karin, Alonso, Jose M.
• Format: Article
• Language: English
• Subjects: Acetic acid; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Auxins; Biochemical pathways; Biosynthesis; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Forest Science; Gene Knockdown Techniques; Indoleacetic Acids - metabolism; Indoles - metabolism; Insulin antibodies; Metabolism; Oxygenases - genetics; Oxygenases - metabolism; Phenotypes; Plant cells; Plant growth; Plants; Seedlings; Skogsvetenskap; Transgenes; Tryptophan Transaminase - genetics; Tryptophan Transaminase - metabolism
• ISSN: 1040-4651; 1532-298X; 1532-298X
• DOI: 10.1105/tpc.111.088047

The effects of auxins on plant growth and development have been known for more than 100 years, yet our understanding of how plants synthesize this essential plant hormone is still fragmentary at best. Gene loss-and gain-of-function studies have conclusively implicated three gene families, CYTOCHROME P450 79B2/B3 [CYP79B2/B3), YUCCA [YUC), and TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1/TRYPTOPHAN AMINOTRANSFERASE-RELATED (TAA1/TAR), in the production of this hormone in the reference plant Arabidopsis thaliana. Each of these three gene families is believed to represent independent routes of auxin biosynthesis. Using a combination of pharmacological, genetic, and biochemical approaches, we examined the possible relationships between the auxin biosynthetic pathways defined by these three gene families. Our findings clearly indicate that TAAI/TARs and YUCs function in a common linear biosynthetic pathway that is genetically distinct from the CYP79B2/B3 route. In the redefined TAA1-YUC auxin biosynthetic pathway, TAA1/TARs are required for the production of indole-3-pyruvic acid (IPyA) from Trp, whereas YUCs are likely to function downstream. These results, together with the extensive genetic analysis of four pyruvate decarboxylases, the putative downstream components of the TAA1 pathway, strongly suggest that the enzymatic reactions involved in indole-3-acetic acid (IAA) production via IPyA are different than those previously postulated, and a new and testable model for how IAA is produced in plants is needed.