Medicago truncatulaSOBIR1 controls specificity in the Rhizobium-legume symbiosis

Abstract

SummaryMedicago truncatulaNod Factor Perception (MtNFP) is a lysin-domain Receptor-Like Kinase (LysM-RLK) that plays a key role in the Rhizobium-legume symbiosis, and is involved in plant immunity. MtNFP also has an inactive kinase domain, suggesting that the protein is involved in different receptor complexes. Using the MtNFP pseudo-kinase domain as a bait in a Yeast two Hybrid screen, we identifiedM. truncatulaSUPPRESSOR OF BIR1 (MtSOBIR1) as a new interactor of MtNFP. We showed that an interaction between the two RLKs can occurin plantaand that the kinase domain of MtSOBIR1 is active and can transphosphorylate the pseudo-kinase domain of MtNFP. Like in other plants, our data suggest a positive role of MtSOBIR1 in immunity;MtSOBIR1could functionally complement anAtsobir1mutant for defence activation, and aMtsobir1mutant was defective in pathogen-induced defence gene expression. We also showed thatMtSOBIR1has a symbiotic role withMtsobir1mutants showing a strong symbiotic phenotype in a plant genotype- and rhizobial strain-specific manner. The symbiotic role was apparent both at an early stage of rhizobial infection and in nodules. Together, these data suggest that, like MtNFP, MtSOBIR1 has a dual role, and can control immunity in both pathogenic and beneficial situations, with positive or negative roles, respectively.