Characterization of immunity-inducing rhizobacteria highlights diversity in plant-microbe interactions

Abstract

AbstractThe narrow region of soil surrounding roots (rhizosphere) contains an astonishing diversity of microorganisms. Some rhizosphere bacteria can improve plant health and immunity, via direct competition with pathogens or by establishing heightened immunity in aboveground tissues, a phenomenon known as Induced Systemic Resistance (ISR). We screened a bacterial library from agricultural soils to identify strains that, after root treatment, induce immunity inSolanum lycopersicum(tomato) against the fungal pathogenBotrytis cinerea. Here, we report the establishment of a screening method and characterization of a subset of five strains, belonging to the speciesBacillus velezensis, Paenibacillus peoriaeandPseudomonas parafulva, that induced systemic resistance in tomato. However interestingly, only two of them triggered canonical ISR in Arabidopsis, indicating plant host specificity and/or alternative modes of actions. Furthermore, some of the strains displayed direct anti-microbial activity. We also found the requirement of the lipid-binding protein DIR1 in ISR establishment, indicating a possible convergence of SAR and ISR signaling. Finally, we found thatP. parafulvaTP18m, also displayed strong effects on root development. Taken together, we have identified taxonomically diverse immunity-inducing bacteria. Our characterization revealed diverse features, highlighting the complexity of bacteria- host interaction in the rhizosphere.HighlightWe identified taxonomically diverse rhizobacteria that induce systemic resistance in tomato plants to Botrytis after application to the root. These bacteria display diverse modes of action to improve plant health.