Innate immunity can distinguish beneficial from pathogenic rhizosphere microbiota

Abstract

For optimal growth and development, hosts depend on their ability to promote healthy symbiotic interactions while restricting pathogen growth. To ask whether hosts can distinguish phylogenetically similar pathogens and beneficial bacteria, we used two closely related plant-associated strains of Pseudomonas fluorescens where one is beneficial and the other exhibits toxin-dependent virulence. We show that while the two strains co-exist in vitro, the beneficial outcompetes that pathogen in planta. Using several readouts for plant innate immunity, we found that the beneficial and pathogenic strains elicit mechanistically distinct immune responses that occur in distinct root compartments. We show that while both the pathogenic and beneficial bacterial have plant recognizable MAMPs, the pathogen uniquely induces MAMP-independent immune responses. We found that the pathogen induces both a toxin-independent and a unique toxin-dependent defense response that remains intact in immune signaling mutants including bak1/bkk1 and npr1/4D. We conclude that hosts can distinguish between phylogenetically similar microbes.