Pantoea ananatis-triggered systemic resistance requires root sensing through the LORE receptor kinase in Arabidopsis

Systemic immunity induced by beneficial bacteria enhances plant resilience to subsequent pathogen attacks. However, the mechanisms by which plants perceive these bacteria and translate this perception into a systemic response remain poorly understood. The Brassicaceae LIPOOLIGOSACCHARIDE-SPECIFIC REDUCED ELICITATION (LORE) receptor kinase is the direct sensor of bacterial medium-chain-length 3-hydroxy fatty acids (mc-3-OH-FAs) and 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs), both of which activate local Brassicaceae immunity. Here, we show that the HAA-producing bacterium Pantoea ananatis BRT175 can colonize Arabidopsis thaliana roots independently of the production of HAAs, but these compounds induce a lore-dependent local immune response in roots. P. ananatis triggers induced systemic resistance (ISR) against the necrotrophic fungus Botrytis cinerea, but not against the hemibiotrophic bacterium Pseudomonas syringae pv. tomato DC3000. This ISR can be mimicked by HAAs or 3-hydroxy-decanoic acid (3-OH-C10), the strongest agonist of LORE. Both bacterium- and 3-hydroxylated fatty acid MAMP-induced ISR against B. cinerea rely on LORE-mediated sensing, involve salicylic acid, jasmonic acid/ethylene signaling pathways, and activate similar defense gene expression profiles in infected leaves. Our results demonstrate that lipidic microbe-associated molecular patterns (MAMPs) produced by beneficial microorganisms are necessary and sufficient to trigger rhizobacteria-mediated ISR and could differentially activate systemic resistance against biotrophic and necrotrophic pathogens.