Root exudates mediate plant defense against foliar pathogens by recruiting beneficial microbes

Plants are capable of releasing specific root exudates to recruit beneficial rhizosphere microbes upon foliar pathogen invasion attack, including long-chain fatty acids, amino acids, short-chain organic acids and sugars. Although long-chain fatty acids and amino acids application have been linked to soil legacy effects that improve future plant performance in the presence of the pathogen, the precise mechanisms involved are to a large extent still unknown. Here, we conditioned soils with long-chain fatty acids and amino acids application (L + A) or short-chain organic acids and sugars (S + S) to examine the direct role of such exudates on soil microbiome structure and function. The L + A treatment recruited higher abundances of Proteobacteria which were further identified as members of the genera Sphingomonas, Pseudomonas, Roseiflexus, and Flavitalea. We then isolated the enriched bacterial strains from these groups, identifying ten Pseudomonas strains that were able to help host plant to resist foliar pathogen infection. Further investigation showed that the L + A treatment resulted in growth promotion of these Pseudomonas strains. Collectively, our data suggest that long-chain fatty acids and amino acids stimulated by foliar pathogen infection can recruit specific Pseudomonas populations that can help protect the host plant or future plant generations.