Symbiosome-targeted peptides enhance nitrogen fixation without terminal differentiation

Legumes have evolved lineage-specific peptides to control rhizobia and sustain nitrogen fixation. In inverted repeat-lacking clade (IRLC) legumes, nodule-specific cysteine-rich (NCR) peptides enforce terminal bacteroid differentiation, maximizing symbiotic output but restricting nodule lifespan. By contrast, Robinioid legumes, the IRLC’s sister clade, lack NCRs yet include perennial species that maintain productive nodules for decades. Here we identify a nodule-specific-proline-glycine-rich peptide family (NPGs) as a conserved, genus-wide innovation of Robinia. NPGs are highly abundant, localize to the symbiosome membrane, and are intrinsically disordered. Exposure of Mesorhizobium robiniaeto recombinant NPGs reprograms physiology, inducing nitrogenase expression while dampening growth without loss of viability. NPGs thus exemplify a distinct, reversible strategy of symbiont control, expanding the peptide repertoire that supports nitrogen fixation in perennial legumes.