Two residues reprogram immunity receptor kinases to signal in nitrogen-fixing symbiosis

Abstract

AbstractReceptor signaling shapes cellular functions and specificity in the signaling output is central for delineating biological processes. In legume root cells, very similar and structurally conserved chitin and Nod factor receptor kinases activate immunity, or symbiosis, respectively after perception of chitinous ligands. Here we show that individual residues in the intracellular part of the Nod factor receptor NFR1 determine signal specificity and efficiency distinguishing immunity and symbiotic signaling. Functional investigation of CERK6, NFR1 and receptor variants hereof revealed a conserved motif that we term Symbiosis Determinant 1 in the juxtamembrane region of the kinase domain that is key for symbiotic signaling. We demonstrate that two residues in Symbiosis Determinant 1 are indispensable hallmarks for NFR1 receptors and are sufficient to convertLotusCERK6 and barley RLK4 functioning in immunity, to initiate symbiotic signaling.