A fungal member of the <i>Arabidopsis thaliana</i> phyllosphere antagonizes <i>Albugo laibachii</i> via a GH25 lysozyme.

Abstract

Plants are not only challenged by pathogenic organisms but also colonized by commensal microbes. The network of interactions these microbes establish with their host and among each other is suggested to contribute to the immune responses of plants against pathogens. In wild <i>Arabidopsis thaliana</i> populations, the oomycete pathogen <i>Albugo laibachii</i> plays an influential role in structuring the leaf phyllosphere. We show that the epiphytic yeast <i>Moesziomyces bullatus</i> ex <i>Albugo</i> on Arabidopsis, a close relative of pathogenic smut fungi, is an antagonistic member of the <i>A. thaliana</i> phyllosphere, which reduces infection of <i>A. thaliana</i> by <i>A. laibachii</i>. Combination of transcriptomics, reverse genetics, and protein characterization identified a GH25 hydrolase with lysozyme activity as a major effector of this microbial antagonism. Our findings broaden the understanding of microbial interactions within the phyllosphere, provide insights into the evolution of epiphytic basidiomycete yeasts, and pave the way for novel biocontrol strategies.