Recognition of Microbe- and Damage-Associated Molecular Patterns by Leucine-Rich Repeat Pattern Recognition Receptor Kinases Confers Salt Tolerance in Plants

In plants, a first layer of inducible immunity is conferred by pattern recognition receptors (PRRs) that bind microbe- and damage-associated molecular patterns to activate pattern-triggered immunity (PTI). PTI is strengthened or followed by another potent form of immunity when intracellular receptors recognize pathogen effectors, termed effector-triggered immunity. Immunity signaling regulators have been reported to influence abiotic stress responses as well, yet the governing principles and mechanisms remain ambiguous. Here, we report that PRRs of a leucine-rich repeat ectodomain also confer salt tolerance in Arabidopsis thaliana, following recognition of cognate ligands such as bacterial flagellin (flg22 epitope) and elongation factor Tu (elf18 epitope), and the endogenous Pep peptides. Pattern-triggered salt tolerance (PTST) requires authentic PTI signaling components; namely, the PRR-associated kinases BAK1 and BIK1 and the NADPH oxidase RBOHD. Exposure to salt stress induces the release of Pep precursors, pointing to the involvement of the endogenous immunogenic peptides in developing plant tolerance to high salinity. Transcriptome profiling reveals an inventory of PTST target genes, which increase or acquire salt responsiveness following a preexposure to immunogenic patterns. In good accordance, plants challenged with nonpathogenic bacteria also acquired salt tolerance in a manner dependent on PRRs. Our findings provide insight into signaling plasticity underlying biotic or abiotic stress cross-tolerance in plants conferred by PRRs.