Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis

• Published in: The Plant journal : for cell and molecular biology 2014-02, Vol.77 (3), p.352-366
• Main Authors: Nishimura, Takeshi, Hayashi, Ken‐ichiro, Suzuki, Hiromi, Gyohda, Atsuko, Takaoka, Chihiro, Sakaguchi, Yusuke, Matsumoto, Sachiko, Kasahara, Hiroyuki, Sakai, Tatsuya, Kato, Jun‐ichi, Kamiya, Yuji, Koshiba, Tomokazu
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - drug effects; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis Proteins - antagonists & inhibitors; Arabidopsis Proteins - genetics; Biosynthesis; Biosynthetic Pathways; coleoptiles; corn; Cotyledon - drug effects; Cotyledon - enzymology; Cotyledon - genetics; Cotyledon - growth & development; Dose-Response Relationship, Drug; Enzymes; Flowers & plants; Gene Expression Regulation, Plant; hypocotyls; IAA biosynthesis inhibitor; indole acetic acid; Indoleacetic Acids - chemistry; Indoleacetic Acids - metabolism; Indoles - metabolism; maize coleoptiles; mutants; Mutation; Oxygenases - antagonists & inhibitors; Oxygenases - genetics; Phenotype; plant development; Plant Growth Regulators - chemistry; Plant Growth Regulators - metabolism; Plant Leaves - drug effects; Plant Leaves - enzymology; Plant Leaves - genetics; Plant Leaves - growth & development; Plant Roots - drug effects; Plant Roots - enzymology; Plant Roots - genetics; Plant Shoots - drug effects; Plant Shoots - enzymology; Plant Shoots - genetics; Plant Shoots - growth & development; Plants, Genetically Modified; Recombinant Fusion Proteins; root growth; seedlings; Seedlings - drug effects; Seedlings - enzymology; Seedlings - genetics; Seedlings - growth & development; Small Molecule Libraries; TAA; Triazoles - chemistry; Triazoles - pharmacology; tryptophan; Tryptophan Transaminase - antagonists & inhibitors; Tryptophan Transaminase - genetics; YUCCA; Zea mays - drug effects; Zea mays - enzymology; Zea mays - genetics; Zea mays - growth & development
• ISSN: 0960-7412; 1365-313X
• DOI: 10.1111/tpj.12399

Indole‐3–acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole‐3–pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5–(4–chlorophenyl)‐4H‐1,2,4–triazole‐3–thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC‐expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1‐His suggested that yucasin strongly inhibited YUC1‐His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over‐expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss‐of‐function mutant of TAA1, sav3–2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l–kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin‐treated sav3–2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.