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Involvement of tryptophan-derived metabolites in the post-invasive resistance of Arabidopsis thaliana against multiple fungal pathogens

Ayumi Kosaka: Kyoto University, Graduate School of Agriculture

<div>A hemibiotrophic pathogen <em>Colletotrichum tropicale</em> (<em>Ctro</em>), formerly called <em>C. gloeosporioides</em>, is not adapted to <em>Arabidopsis thaliana </em>but is able to invade the <em>Arabidopsis pen2</em> mutant. However, once <em>Ctro</em> enters <em>pen2</em>, its further expansion is blocked by post-invasive defense. The <em>pen2 pad3</em> mutant exhibits a reduction in post-invasive resistance against <em>Ctro</em>. Here we investigated the post-invasive resistance against <em>Ctro</em> in the <em>pen2 cyp71A12 cyp71A13 </em>mutant. <em>Ctro </em>was inoculated on tested plant lines, and the inoculated leaves were collected and stained with trypan blue. Microscopic observation showed that the triple mutant exhibited enhanced reduction in the resistance compared with <em>pen2 pad3</em>. We further found the post-invasive resistance reduced in <em>pen2 cyp71A12, </em>similar to <em>pen2 pad3</em>. Similar phenomenon was observed in the interaction between adapted <em>C. higginsianum</em> and the same <em>A. thaliana</em> mutants. These findings suggest that the post-invasive resistance against hemibiotrophic <em>Colletotrichum</em> fungi needs (i) the CYP71A12-dependent synthesis of indole-3-carboxylic acid and/or related compounds (I3CAs) and (ii) the CYP71A13 and PAD3-dependent synthesis of camalexin. Notably, the <em>pen2 cyp71A12 cyp71A13 </em>mutant exhibits reduced resistance against the necrotrophic pathogen <em>Alternaria brassicicola</em>, as compared with <em>pen2 pad3</em>. Therefore, both I3CAs and camalexin are involved in post-invasive resistance against fungal pathogens with distinct infection strategies.</div>