Genome-Wide Identification of the CrRLK1L Subfamily and Comparative Analysis of Its Role in the Legume-Rhizobia Symbiosis

The plant receptor-like-kinase subfamily CrRLK1L has been widely studied, and CrRLK1Ls have been described as crucial regulators in many processes inArabidopsis thaliana(L.), Heynh. Little is known, however, about the functions of these proteins in other plant species, including potential roles in symbiotic nodulation. We performed a phylogenetic analysis of CrRLK1L subfamily receptors of 57 different plant species and identified 1050 CrRLK1L proteins, clustered into 11 clades. This analysis revealed that the CrRLK1L subfamily probably arose in plants during the transition from chlorophytes to embryophytes and has undergone several duplication events during its evolution. Among theCrRLK1Lsof legumes andA. thaliana, protein structure, gene structure, and expression patterns were highly conserved. Some legumeCrRLK1Lgenes were active in nodules. A detailed analysis of eight nodule-expressed genes inPhaseolus vulgarisL. showed that these genes were differentially expressed in roots at different stages of the symbiotic process. These data suggest thatCrRLK1Lsare both conserved and underwent diversification in a wide group of plants, and shed light on the roles of these genes in legume-rhizobia symbiosis.