Abstract
Among several receptor-like kinases (RLKs), leucine-rich-repeat receptor-like kinases (LRR-RLKs) are a major group of genes that play crucial roles in growth, development and stress responses in plant systems. Given that they have several functional roles, it is important to investigate their roles in Brassica rapa. In the present study, 303 LRR-RLKs were identified in the genome of B. rapa and comparative phylogenetic analysis of 1213 combined LRR-RLKs of B. rapa, Arabidopsis thaliana, Oryza sativa and Populus trichocarpa helped us to categorize the gene family into 15 subfamilies based on their sequence and structural similarities. The chromosome localizations of 293 genes allowed the prediction of duplicates, and motif conservation and intron/exon patterns showed differences among the B. rapa LRR-RLK (BrLRR-RLK) genes. Additionally, computational function annotation and expression analysis was used to predict their possible functional roles in the plant system. Biochemical results for 11 selected genes showed variations in phosphorylation activity. Interestingly, BrBAK1 showed strong auto-phosphorylation and trans-phosphorylation on its tyrosine and threonine residues compared with AtBAK1 in previous studies. The AtBAK1 receptor kinase is involved in plant growth and development, plant innate immunity, and programmed cell death, and our results suggest that BrBAK1 might also be involved in the same functions. Another interesting result was that BrBAK1, BrBRI1, BrPEPR1 and BrPEPR2 showed activity with both anti-phosphotyrosine and anti-phosphothreonine antibodies, indicating that they might have dual-specificity kinase activity. This study provides comprehensive results for the BrLRR-RLKs, revealing expansion of the gene family through gene duplications, structural similarities and variations among the genes, and potential functional roles according to gene ontology, transcriptome profiling and biochemical analysis.
Highlights
The Brassicaceae family is one of the major groups in the plant kingdom, composed of 340– 360 genera and over 3,700 species distributed worldwide [1]
A total of 303 non-redundant BrLRR-receptor-like kinases (RLKs) genes were identified in the B. rapa genome and were confirmed through manual and Pfam searches for the presence of both extracellular domain (ECD) and kinase domains (KDs) in the sequences
Most of the BrLRR-RLK genes contained leucine rich repeats (LRRs) in their ECDs, which play a major role in protein–protein interactions [6], whereas transmembrane (TM) domains and signal peptides (SP) are signatures of membrane RLK proteins [5]
Summary
The Brassicaceae family is one of the major groups in the plant kingdom, composed of 340– 360 genera and over 3,700 species distributed worldwide [1]. Leucine-rich-repeat receptor-like kinases (LRR- RLK) form one of the major super-families in plant species and consist of an N-terminal LRR as an extracellular domain (ECD) and a Cterminal kinase domain. The LRR domain is 20–30 amino acids in length, is the major class of ECD [5] found among all of the RLKs in plant species, and is predicted to be involved in protein–protein interactions [6]. The protein kinase domain forms a lobe structure that consists of approximately 250–300 amino acids and has two sub-divisions, protein-serine/threonine kinases and protein tyrosine kinases It is divided into twelve sub-domains that are highly conserved and involved in catalytic activity, in functions related to cell development [7]. Non-RD kinases are mainly involved in plant immunity against microbes [18,19]
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