Glutathione-Indole-3-Acetonitrile Is Required for Camalexin Biosynthesis in Arabidopsis thaliana

• Published in: The Plant cell Vol. 23; no. 1; pp. 364 - 380
• Main Authors: Su, Tongbing, Xu, Juan, Li, Yuan, Lei, Lei, Zhao, Luo, Yang, Hailian, Feng, Jidong, Liu, Guoqin, Ren, Dongtao
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 2011
• Subjects: Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Biosynthesis; Enzymes; Gels; Gene Expression Regulation, Plant; Gene Knockout Techniques; Genes; Glutathione - metabolism; Glutathione Transferase - genetics; Glutathione Transferase - metabolism; Goods and services tax; Indoles - metabolism; Mitogen-Activated Protein Kinase Kinases; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Mutagenesis, Insertional; Plant cells; Plants; Plants, Genetically Modified - genetics; Plants, Genetically Modified - metabolism; Seedlings; Thiazoles - metabolism; Transgenic plants; Yeasts
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.110.079145

Camalexin, a major phytoalexin in Arabidopsis thaliana, consists of an indole ring and a thiazole ring. The indole ring is produced from Trp, which is converted to indole-3-acetonitrile (IAN) by CYP79B2/CYP79B3 and CYP71A13. Conversion of Cys(IAN) to dihydrocamalexic acid and subsequently to camalexin is catalyzed by CYP71B15. Recent studies proposed that Cys derivative, not Cys itself, is the precursor of the thiazole ring that conjugates with IAN. The nature of the Cys derivative and how it conjugates to IAN and subsequently forms Cys(IAN) remain obscure. We found that protein accumulation of multiple glutathione S-transferases (GSTs), elevation of GST activity, and consumption of glutathione (GSH) coincided with camalexin production. GSTF6 overexpression increased and GSTF6-knockout reduced camalexin production. Arabidopsis GSTF6 expressed in yeast cells catalyzed GSH(IAN) formation. GSH(IAN), (IAN)CysGly, and γGluCys(IAN) were determined to be intermediates within the camalexin biosynthetic pathway. Inhibitor treatments and mutant analyses revealed the involvement of γ-glutamyl transpeptidases (GGTs) and phytochelatin synthase (PCS) in the catabolism of GSH(IAN). The expression of GSTF6, GGT1, GGT2, and PCS1 was coordinately upregulated during camalexin biosynthesis. These results suggest that GSH is the Cys derivative used during camalexin biosynthesis, that the conjugation of GSH with IAN is catalyzed by GSTF6, and that GGTs and PCS are involved in camalexin biosynthesis.