A fungal powdery mildew pathogen induces extensive local and marginal systemic changes in the Arabidopsis thaliana microbiota

Abstract

Summary Powdery mildew is a foliar disease caused by epiphytically growing obligate biotrophic ascomycete fungi. How powdery mildew colonization affects host resident microbial communities locally and systemically remains poorly explored. We performed powdery mildew ( Golovinomyces orontii ) infection experiments with Arabidopsis thaliana grown in either natural soil or a gnotobiotic system and studied the influence of pathogen invasion into standing natural multi‐kingdom or synthetic bacterial communities (SynComs). We found that after infection of soil‐grown plants, G . orontii outcompeted numerous resident leaf‐associated fungi while fungal community structure in roots remained unaltered. We further detected a significant shift in foliar but not root‐associated bacterial communities in this setup. Pre‐colonization of germ‐free A . thaliana leaves with a bacterial leaf‐derived SynCom, followed by G . orontii invasion, induced an overall similar shift in the foliar bacterial microbiota and minor changes in the root‐associated bacterial assemblage. However, a standing root‐derived SynCom in root samples remained robust against foliar infection with G . orontii . Although pathogen growth was unaffected by the leaf SynCom, fungal infection caused a twofold increase in leaf bacterial load. Our findings indicate that G . orontii infection affects mainly microbial communities in local plant tissue, possibly driven by pathogen‐induced changes in source‐sink relationships and host immune status.

Bibliographic Information