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

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

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Botanical Institute and Cluster of Excellence on Plant Sciences (CEPLAS), University of Cologne, BioCenter, Zülpicher Straße 47b, 50674 Cologne, Germany.
Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego12/14, 61-704 Poznań, Poland.
Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Campus Montegancedo, Pozuelo de Alarcón, 28223 Madrid, Spain.
Lehrstuhl für Genetik, Technische Universität München, Emil-Ramann-Str. 8, 85354 Freising, Germany.
Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego12/14, 61-704 Poznań, Poland. Electronic address:


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.


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

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