Stealth mode: How Rhodanobacter R179 evades plant immunity

The soil microbiome harbors a vast diversity of microorganisms that can be pathogenic, beneficial, or commensal to plants. A fundamental question in plant biology is how plants actively detect, differentiate, and optimize their associations with the microbiome to maintain optimal fitness. In a recent study, Ordon and colleagues took an alternative approach—exploring how bacteria evade plant immune surveillance. The bacterial families Xanthomonadaceae and Rhodanobacteraceae include both commensal and pathogenic strains. Interestingly, Rhodanobacter R179, a root commensal belonging to a branch of Xanthomonadales, possesses immunogenic elicitors recognized by the plant immune receptors EFR and SOBIR1. However, it does not trigger a pattern-triggered immunity (PTI) response, such as flg22-induced root growth inhibition (RGI). By screening a collection of R179 mutants, the researchers identified two transporter complex mutants, dssA and dssB, which fail to mediate peptidase secretion and become sensitive to flg22-induced RGI. The ability to secrete peptidase allows R179 to eliminate immunogenic peptides and evade plant immunity. This effect extends beyond R179, as the secreted peptidase influences other microbiota members within the soil matrix. In a community context, R179 promotes microbiota diversity but at the cost of increased metabolic constraints on itself. The rationale and mechanism behind this coexistence and its ecological niche remain intriguing and warrant further investigation. (Summary by Ching Chan @ntnuchanlab) Nature Plants 10.1038/s41477-025-01918-w