Abstract
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 in Medicago truncatula. Our genome-wide analysis revealed 329 LRR-RLK genes in the M. truncatula genome. 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-seven M. truncatula LRR-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 that LRR-RLKs were differentially expressed among different tissues, while some were expressed specifically in the roots and nodules. The expression of LRR-RLKs in A17 and 4 nodule mutants under rhizobial infection showed that 36 LRR-RKLs were highly upregulated in the sickle (skl) mutant [an ethylene (ET)-insensitive, Nod factor-hypersensitive mutant] after 12 h of rhizobium inoculation. Among these LRR-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 the LRR-RLK gene family in M. truncatula and serve as a guide for functional research of the LRR-RLKs.
Highlights
Transmembrane receptor kinases play critical roles in both animal and plant signaling pathways involved in the regulation of growth, development, differentiation, cell death, and defense responses to pathogens [1,2,3]
By comparing the whole genomes of M. truncatula and Arabidopsis via MCScanX to analyze the synteny between the two species, we identified a total of 43 gene pairs with synteny (Figure 6a, Table S6)
With respect to legume species, the leucine-rich repeat (LRR)-receptor-like kinases (RLKs) family in soybean has been identified, which has members according to previous studies [45], and in this study, we identified a total of 329 members in M. truncatula (Table S1)
Summary
Transmembrane receptor kinases play critical roles in both animal and plant signaling pathways involved in the regulation of growth, development, differentiation, cell death, and defense responses to pathogens [1,2,3]. Pelle and related cytoplasmic kinases fall within the plant RLK clade, which has been defined as the RLK/Pelle family [5,6,7]. RLKs are classified into two broad categories on the basis of whether their transmembrane proteins have extracellular domains—receptor-like cytoplasmic kinases (RLCKs). Life 2020, 10, 176 and receptor-like protein kinases (RLKs) [6,7,8,9]. A typical RLK contains an extracellular domain, transmembrane domain and intracellular kinase domain; RLKs constitute one of the largest gene families in flowering plants such as Arabidopsis. The first plant RLK gene was found and cloned in maize and was shown to encode a receptor kinase protein [10]. In Arabidopsis alone, it has been reported that there are at least 610 RLK members, representing nearly 2.5% of Arabidopsis protein-coding genes [1]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
