J Integr Plant Biol. ›› 2012, Vol. 54 ›› Issue (7): 471-485.DOI: 10.1111/j.1744-7909.2012.01131.x

• Metabolism and Biochemistry • Previous Articles     Next Articles

Arabidopsis Acetyl-Amido Synthetase GH3.5 Involvment in Camalexin Biosynthesis through Conjugation of Indole-3-Carboxylic Acid and Cysteine and Upregulation of Camalexin Biosynthesis Genes

Mu-Yang Wang1, Xue-Ting Liu2, Ying Chen1, Xiao-Jing Xu3, Biao Yu2, Shu-Qun Zhang4, Qun Li1* and Zu-Hua He1*   

  1. 1National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China
    2Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
    3National Engineering Center for BioChip at Shanghai, Shanghai 201203, China
    4Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA
  • Received:2012-05-10 Accepted:2012-05-16 Published:2012-05-25
  • About author:*Corresponding authors Tel: +86 21 5492 4121; Fax: +86 21 5492 4123; Email: zhhe@sibs.ac.cn or Tel: +86 21 5492 4122; Fax: +86 21 5492 4123; Email: qli@sibs.ac.cn

Abstract:

Camalexin (3-thiazol-2′-yl-indole) is the major phytoalexin found in Arabidopsis thaliana. Several key intermediates and corresponding enzymes have been identified in camalexin biosynthesis through mutant screening and biochemical experiments. Camalexin is formed when indole-3-acetonitrile (IAN) is catalyzed by the cytochrome P450 monooxygenase CYP71A13. Here, we demonstrate that the Arabidopsis GH3.5 protein, a multifunctional acetyl-amido synthetase, is involved in camalexin biosynthesis via conjugating indole-3-carboxylic acid (ICA) and cysteine (Cys) and regulating camalexin biosynthesis genes. Camalexin levels were increased in the activation-tagged mutant gh3.5–1D in both Col-0 and cyp71A13–2 mutant backgrounds after pathogen infection. The recombinant GH3.5 protein catalyzed the conjugation of ICA and Cys to form a possible intermediate indole-3-acyl-cysteinate (ICA(Cys)) in vitro. In support of the in vitro reaction, feeding with ICA and Cys increased camalexin levels in Col-0 and gh3.5–1D. Dihydrocamalexic acid (DHCA), the precursor of camalexin and the substrate for PAD3, was accumulated in gh3.5–1D/pad3–1, suggesting that ICA(Cys) could be an additional precursor of DHCA for camalexin biosynthesis. Furthermore, expression of the major camalexin biosynthesis genes CYP79B2, CYP71A12, CYP71A13 and PAD3 was strongly induced in gh3.5–1D. Our study suggests that GH3.5 is involved in camalexin biosynthesis through direct catalyzation of the formation of ICA(Cys), and upregulation of the major biosynthetic pathway genes.

Key words: Arabidopsis, GH3.5, indole-3-carboxylic acid, cysteine, camalexin biosynthesis

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