Chitin Deacetylases Are Required for <i>Epichloë festucae</i> Endophytic Cell Wall Remodeling During Establishment of a Mutualistic Symbiotic Interaction with <i>Lolium perenne</i>

Abstract

<i>Epichloë festucae</i> forms a mutualistic symbiotic association with <i>Lolium perenne</i>. This biotrophic fungus systemically colonizes the intercellular spaces of aerial tissues to form an endophytic hyphal network and also grows as an epiphyte. However, little is known about the cell wall-remodeling mechanisms required to avoid host defense and maintain intercalary growth within the host. Here, we use a suite of molecular probes to show that the <i>E. festucae</i> cell wall is remodeled by conversion of chitin to chitosan during infection of <i>L. perenne</i> seedlings, as the hyphae switch from free-living to endophytic growth. When hyphae transition from endophytic to epiphytic growth, the cell wall is remodeled from predominantly chitosan to chitin. This conversion from chitin to chitosan is catalyzed by chitin deacetylase. The genome of <i>E. festucae</i> encodes three putative chitin deacetylases, two of which (<i>cdaA</i> and <i>cdaB</i>) are expressed in planta. Deletion of either of these genes results in disruption of fungal intercalary growth in the intercellular spaces of plants infected with these mutants. These results establish that these two genes are required for maintenance of the mutualistic symbiotic interaction between <i>E. festucae</i> and <i>L. perenne</i>.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.