Fig. 1.

Schematic illustration of genetic components involved in legume-rhizobia symbiotic signaling. NF are perceived by a receptor complex containing NFP. Perception of NF triggers early responses, like ion fluxes, depolarization of plasma membrane, production of reactive oxygen species (ROS), and cytoplasmic alkalinization. The signals are transduced downstream to activate LRR-receptor kinase, DMI2 and DMI1. The nuclear ion channel DMI1 is required for NF-induced nuclear calcium spiking. Later these calcium signals are perceived and decoded by calcium/calmodulin-dependent protein kinase, DMI3, which acts as a central player in the NF signaling and coordinates the expression of symbiotic genes, including early nodulin genes. NF signaling culminates with the coordinated and synchronous progression of infection and cortical cell division, resulting in the formation of mature, infected and nitrogen-fixing nodules.