A general non-self response as part of plant immunity

Plants, like other multicellular organisms, are colonized by microorganisms. How plants respond to their microbiota is currently not well understood. We used a phylogenetically diverse set of 39 native bacterial strains from Arabidopsis thaliana leaves to assess host transcriptional and metabolic adaptations to bacterial encounters. We identified a molecular response, which we termed the general non-self response (GNSR) that involves the expression of a core set of 24 genes. The GNSR genes are not only consistently induced by the presence of the majority of strains, they also comprise the most differentially regulated genes across treatments and are predictive of a hierarchical transcriptional reprogramming beyond the GNSR. Using a complementary untargeted metabolomics approach we link the GNSR to the tryptophan derived secondary metabolism, highlighting the importance of small molecules in plant microbe interactions. We demonstrate that seven of the GNSR genes, namely CHX16, IGMT3, MLO12, CYP71A12, PRX71, GSTF6 and AT2G43620, are required for resistance against the bacterial pathogen Pseudomonas syringae. Our results suggest that the GNSR constitutes a defense adaptation strategy that is consistently elicited by diverse strains from various phyla, contributes to host protection and involves secondary metabolism.