Abstract
BackgroundLeucine-rich repeat receptor-like protein kinases (LRR-RLKs) are the largest group of receptor-like kinases in plants and play crucial roles in development and stress responses. The evolutionary relationships among LRR-RLK genes have been investigated in flowering plants; however, no comprehensive studies have been performed for these genes in more ancestral groups. The subfamily classification of LRR-RLK genes in plants, the evolutionary history and driving force for the evolution of each LRR-RLK subfamily remain to be understood.ResultsWe identified 119 LRR-RLK genes in the Physcomitrella patens moss genome, 67 LRR-RLK genes in the Selaginella moellendorffii lycophyte genome, and no LRR-RLK genes in five green algae genomes. Furthermore, these LRR-RLK sequences, along with previously reported LRR-RLK sequences from Arabidopsis thaliana and Oryza sativa, were subjected to evolutionary analyses. Phylogenetic analyses revealed that plant LRR-RLKs belong to 19 subfamilies, eighteen of which were established in early land plants, and one of which evolved in flowering plants. More importantly, we found that the basic structures of LRR-RLK genes for most subfamilies are established in early land plants and conserved within subfamilies and across different plant lineages, but divergent among subfamilies. In addition, most members of the same subfamily had common protein motif compositions, whereas members of different subfamilies showed variations in protein motif compositions. The unique gene structure and protein motif compositions of each subfamily differentiate the subfamily classifications and, more importantly, provide evidence for functional divergence among LRR-RLK subfamilies. Maximum likelihood analyses showed that some sites within four subfamilies were under positive selection.ConclusionsMuch of the diversity of plant LRR-RLK genes was established in early land plants. Positive selection contributed to the evolution of a few LRR-RLK subfamilies.
Highlights
Leucine-rich repeat receptor-like protein kinases (LRR-Receptor-like kinases (RLK)) are the largest group of receptor-like kinases in plants and play crucial roles in development and stress responses
Some leucine-rich repeat RLK family (LRR-RLK) are involved in the control of plant growth and development; for example, CLV1 is involved in controlling meristem development [6, 7], RUL1 is involved in secondary growth [8], SERK1 is involved in microsporogenesis
As shown in the maximum likelihood (ML) tree (Fig. 1 and Additional file 2: Figure S1), the LRR-RLK genes clearly fell into distinct clades, indicating that these natural groups can be assigned to different subfamilies
Summary
Leucine-rich repeat receptor-like protein kinases (LRR-RLKs) are the largest group of receptor-like kinases in plants and play crucial roles in development and stress responses. All living organisms sense and conduct signals through cell surface receptors In plants, many such cellular signaling transductions are mediated by receptor-like kinases (RLKs). Some LRR-RLKs respond to abiotic and biotic stresses, such as FLS2- and EFR-mediated plant resistance against bacterial pathogens [11, 12], and NIK activity in antiviral defense [13, 14]. Some LRR-RLK genes have dual roles in development and defense due to crosstalk between these two pathways or recognition of multiple ligands by the same receptor [15]. LRR-RLK genes have been extensively studied and the results show that they have crucial roles in plant development and stress responses. There are numerous LRR-RLK genes, and the functions of the vast majority of them are largely unknown
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