Genome-Wide Identification of Rubber Tree LRR-RLK Genes and Functional Characterization of HbPSKR2 (HbLRR-RLK174)

As one of the largest gene families in plants, the Leucine-Rich Repeat Receptor-Like Kinase (LRR-RLK) genes are involved in important biological processes, such as plant growth and development and response to bio-/abiotic stresses. The rubber tree (Hevea brasiliensis Müll. Arg.) is the primary commercial source of natural rubber globally. In this study, 274 LRR-RLK genes were comprehensively identified and classified into 21 subclades of the rubber tree genome. Members belonging to the same subclade exhibited comparable gene structures and possessed conserved protein motifs. Gene duplication analysis detected 35 tandem duplication genes and 81 segmental duplication genes. Cis-element analysis of HbLRR-RLK promoters identified light, hormone, stress, and development-related cis-elements. Tissue-specific expression profiling revealed that 73% (200/274) of HbLRR-RLKs were expressed in at least one of seven analyzed tissues. Protein–protein interaction (PPI) network identified 584 potential interactions among the HbLRR-RLKs. Additionally, subcellular localization analysis suggested that HbPSKR2 (HbLRR-RLK174) is a plasma membrane-localized receptor, and the gene could restore the short-root phenotype of the atpskr mutant in Arabidopsis. These results provide a comprehensive structure to facilitate analysis of the evolution and functional diversification of LRR-RLKs in the rubber tree.