Symbiosome-targeted peptides enhance nitrogen fixation without terminal differentiation [Bacteria RNA-seq]

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 yet include perennial species that maintain productive nodules for decades.

Here we identify a nodule-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 robiniae to recombinant NPGs reprograms physiology, inducing nitrogenase expression while dampening growth without loss of viability.