<i>Colletotrichum higginsianum</i> extracellular LysM proteins play dual roles in appressorial function and suppression of chitin‐triggered plant immunity

<jats:title>Summary</jats:title><jats:p> <jats:list list-type="bullet"> <jats:list-item><jats:p>The genome of the hemibiotrophic anthracnose fungus, <jats:italic>Colletotrichum higginsianum</jats:italic>, encodes a large repertoire of candidate‐secreted effectors containing LysM domains, but the role of such proteins in the pathogenicity of any <jats:italic>Colletotrichum</jats:italic> species is unknown.</jats:p></jats:list-item> <jats:list-item><jats:p>Here, we characterized the function of two effectors, Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>1 and Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>2, which are transcriptionally activated during the initial intracellular biotrophic phase of infection.</jats:p></jats:list-item> <jats:list-item><jats:p>Using immunocytochemistry, we found that Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>2 is concentrated on the surface of bulbous biotrophic hyphae at the interface with living host cells but is absent from filamentous necrotrophic hyphae. We show that recombinant Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>1 and Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>2 bind chitin and chitin oligomers <jats:italic>in vitro</jats:italic> with high affinity and specificity and that both proteins suppress the chitin‐triggered activation of two immune‐related plant mitogen‐activated protein kinases in the host <jats:italic>Arabidopsis</jats:italic>. Using <jats:styled-content style="fixed-case">RNA</jats:styled-content>i‐mediated gene silencing, we found that <jats:italic>Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>1</jats:italic> and <jats:italic>Ch<jats:styled-content style="fixed-case">ELP</jats:styled-content>2</jats:italic> are essential for fungal virulence and appressorium‐mediated penetration of both <jats:italic>Arabidopsis</jats:italic> epidermal cells and cellophane membranes <jats:italic>in vitro</jats:italic>.</jats:p></jats:list-item> <jats:list-item><jats:p>The findings suggest a dual role for these LysM proteins as effectors for suppressing chitin‐triggered immunity and as proteins required for appressorium function.</jats:p></jats:list-item> </jats:list> </jats:p>