A kinase mediator of rhizobial symbiosis and immunity in Medicago.

Abstract

Legume roots secure nitrogen by forming a symbiosis with soil rhizobia but remain resistant to pathogenic bacteria1-4. How this tolerance to rhizobia is achieved without compromising plant immunity is largely unknown. Here, we identify the cytoplasmic kinase MtLICK1/2, which interacts with nodulation factor receptor MtLYK3 to drive symbiotic signaling and suppress plant immunity. Rhizobial infection and nodule development are defective in Mtlick1/2, phenocopying the Mtlyk3-1 mutant. MtLICK1/2 and MtLYK3 undergo reciprocal trans-phosphorylation during rhizobial symbiosis. Phosphorylated MtLYK3 activates the receptor-like kinase MtDMI2 to stimulate symbiotic signaling. MtLICK1/2 is activated in the rhizobia infection area to suppress plant immunity. Thus, MtLICK1/2 and MtLYK3 together amplify symbiotic signaling and dampen host immunity to enable legume-rhizobium symbiosis.