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The Colletotrichum orbiculare MTF4 is a transcription factor downstream of MOR required for plant-derived signal dependent appressorium development

Yasuyuki Kubo: Kyoto Prefectural University

<div>Many plant pathogenic fungi including <em>Colletotrichum</em> species form a specialized infection structure, called an appressorium. Appressorium formation relies on perception of physical and biochemical signals at the plant surface. In cucumber anthracnose fungus <em>C. orbiculare,</em> the morphogenesis-related NDR (nuclear Dbf2-related) kinase pathway (MOR) is crucial for translating plant-derived signals for appressorium development (Kodama <em>et al</em>., 2017). Based on whole genome transcript profiling, we identified the transcription factor <em>MTF4</em> (MOR-related transcription factor 4) as a putative downstream target of MOR. The <em>mtf4 </em>mutant phenotype was closely similar to the MOR component <em>pag1</em> mutant. Introduction of the constitutively active variant of the NDR kinase Cbk1 had no effect on <em>mtf4</em> mutant phenotypes, while introduction of overexpression construct of <em>MTF4</em> to <em>pag1</em> mutant complemented <em>pag1</em> defects. These results suggest that <em>MTF4</em> acts downstream of MOR for appressorium morphogenesis and pathogenesis. Furthermore, Mtf4 was recognized at nuclei during appressorium formation <em>in planta</em> but not<em> in vitro</em>. Mtf4 mis-localized by the conditional inactivation of Cbk1 and <em>pag1</em> deletion, suggesting that MOR-dependent localization of Mtf4 responds to plant-derived signals during appressorium development. Therefore, <em>MTF4</em> is a key downstream transcription factor of MOR in <em>C. orbiculare</em> for appressorium development in response to plant-derived signals.</div>