Genome-Wide Characterization, Evolution, And Expression Analysis Of The Leucine-Rich Repeat Receptor-Like Protein Kinase (Lrr-Rlk) Gene Family Inmedicago Truncatula

Leucine-rich repeat receptor-like kinases (LRR-RLKs) constitute the largest subfamily of receptor-like kinases (RLKs) in plants. They play roles in plant growth and developmental and physiological processes, but less is known about the functions of LRR-RLKs inMedicago truncatula. Our genome-wide analysis revealed 329LRR-RLKgenes in theM.truncatulagenome. Phylogenetic and classification analysis suggested that these genes could be classified into 15 groups and 24 subgroups. A total of 321 genes were mapped onto all chromosomes, and 23 tandem duplications (TDs) involving 56 genes were distributed on each chromosome except 4. Twenty-sevenM.truncatulaLRR-RLK segmental duplication gene pairs were colinearly related. The exon/intron organization, motif composition and arrangements were relatively conserved among members of the same groups or subgroups. Using publicly available RNAseq data and quantitative real-time polymerase chain reaction (qRT-PCR), expression profiling suggested thatLRR-RLKswere differentially expressed among different tissues, while some were expressed specifically in the roots and nodules. The expression ofLRR-RLKsin A17 and 4 nodule mutants under rhizobial infection showed that 36LRR-RKLswere highly upregulated in thesickle(skl) mutant [an ethylene (ET)-insensitive, Nod factor-hypersensitive mutant] after 12 h of rhizobium inoculation. Among theseLRR-RLKs, six genes were also expressed specifically in the roots and nodules, which might be specific to the Nod factor and involved in autoregulation of the nodulation signal. Our results provide information on theLRR-RLKgene family inM. truncatulaand serve as a guide for functional research of theLRR-RLKs.