Reprogramming, not silencing: How plant immunity is gated during legume nodulation

Legume– Rhizobium symbiosis requires rhizobial entry and intracellular persistence without triggering host defense. Recent genetic and biochemical studies support an immune-gating view in which plant immunity pathways are not simply suppressed, but are dynamically regulated throughout rhizobial infection, nodule development and nodule senescence. Here, we review how LysM/LRR receptor complexes and co-receptor availability shape early discrimination of symbiotic signals and immune elicitors and how shared signaling modules (Ca 2+ , ROS and MAPKs) are differentially regulated to permit infection and nodule organogenesis. We then discuss rhizobial surface polysaccharides and type III-secreted effectors as modulators of these thresholds and highlight nodule-local regulators that prevent late immune reactivation and maintain bacteroid accommodation. We also discuss nodule-specific, regulator autophagy-associated processes and, in some legumes, NCR peptides that maintain bacteroids within symbiosomes while preventing plant overactivation of immunity.