Regulation of Pathogen-Triggered Tryptophan Metabolism in Arabidopsis thaliana by MYB Transcription Factors and Indole Glucosinolate Conversion Products

Mol Plant. 2016 May 2;9(5):682-695. doi: 10.1016/j.molp.2016.01.006. Epub 2016 Jan 21.


MYB34, MYB51, and MYB122 transcription factors are known as decisive regulators of indolic glucosinolate (IG) biosynthesis with a strong impact on expression of genes encoding CYP79B2 and CYP79B3 enzymes that redundantly convert tryptophan to indole-3-acetaldoxime (IAOx). This intermediate represents a branching point for IG biosynthesis, and pathways leading to camalexin and indole-carboxylic acids (ICA). Here we investigate how these MYBs affect the pathogen-triggered Trp metabolism. Our experiments indicated that these three MYBs affect not only IG production but also constitutive biosynthesis of other IAOx-derived metabolites. Strikingly, the PENETRATION 2 (PEN2)-dependent IG-metabolism products, which are absent in myb34/51/122 and pen2 mutants, were indispensable for full flg22-mediated induction of other IAOx-derived compounds. However, gene induction and accumulation of ICAs and camalexin upon pathogen infection was not compromised in myb34/51/122 plants, despite strongly reduced IG levels. Hence, in comparison with cyp79B2/B3, which lacks all IAOx-derived metabolites, we found myb34/51/122 an ideal tool to analyze IG contribution to resistance against the necrotrophic fungal pathogen Plectosphaerella cucumerina. The susceptibility of myb34/51/122 was similar to that of pen2, but much lower than susceptibility of cyp79B2/B3, indicating that MYB34/51/122 contribute to resistance toward P. cucumerina exclusively through IG biosynthesis, and that PEN2 is the main leaf myrosinase activating IGs in response to microbial pathogens.

Keywords: MAMP-triggered immunity; Plectosphaerella cucumerina; Trp metabolism; camalexin; indole-3-carboxylic acids; indolic glucosinate.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / metabolism*
  • Arabidopsis / microbiology*
  • Arabidopsis Proteins / metabolism*
  • Ascomycota / pathogenicity
  • Cytochrome P-450 Enzyme System / metabolism
  • Gene Expression Regulation, Plant
  • Indoles / metabolism
  • N-Glycosyl Hydrolases / metabolism
  • Oximes / metabolism
  • Plant Immunity / physiology
  • Transcription Factors / metabolism*
  • Tryptophan / metabolism*


  • Arabidopsis Proteins
  • Indoles
  • MYB122 protein, Arabidopsis
  • MYB34 protein, Arabidopsis
  • MYB36 protein, Arabidopsis
  • MYB51 protein, Arabidopsis
  • Oximes
  • Transcription Factors
  • indole-3-acetaldoxime
  • Tryptophan
  • Cytochrome P-450 Enzyme System
  • cytochrome P-450 79B2 protein, Arabidopsis
  • cytochrome P-450 CYP79B3, Sinapis alba
  • N-Glycosyl Hydrolases
  • PEN2 protein, Arabidopsis