Plant-activated Bacterial Receptor Adenylate Cyclases Modulate Epidermal Infection in the Sinorhizobium meliloti-Medicago Symbiosis

Legumes and soil bacteria called rhizobia have co-evolved a facultative nitrogen-fixing symbiosis. Establishment of the symbiosis requires bacterial entry via root hair infection threads (ITs) and, in parallel, organogenesis of nodules that are subsequently invaded by bacteria. Tight control of nodulation and infection is required to maintain the mutualistic character of the interaction. Available evidence supports a passive bacterial role in nodulation and infection, after the microsymbiont has triggered the symbiotic plant developmental program.