| Summary: | Brassinosteroids (BRs) are important for plant growth and development, with BRI1 and BAK1 kinases playing an important role in BR signal transduction. Latex from rubber trees is crucial for industry, medicine and defense use. Therefore, it is beneficial to characterize and analyze <i>HbBRI1</i> and <i>HbBAK1</i> genes to improve the quality of the resources obtained from <i>Hevea brasiliensis</i> (rubber tree). Based on bioinformatics predictions and rubber tree database, five <i>HbBRI1s</i> with four <i>HbBAK1s</i> were identified and named <i>HbBRI1</i>~<i>HbBRL3</i> and <i>HbBAK1a</i>~<i>HbBAK1d</i>, respectively, which were clustered in two groups. HbBRI1 genes, except for <i>HbBRL3</i>, exclusively contain introns, which is convenient for responding to external factors, whereas <i>HbBAK1b/c/d</i> contain 10 introns and 11 exons, and <i>HbBAK1a</i> contains eight introns. Multiple sequence analysis showed that HbBRI1s include typical domains of the BRI1 kinase, indicating that HbBRI1s belong to BRI1. HbBAK1s that possess LRR and STK_BAK1_like domains illustrate that HbBAK1s belong to the BAK1 kinase. BRI1 and BAK1 play an important role in regulating plant hormone signal transduction. Analysis of the cis-element of all HbBRI1 and HbBAK1 genes identified hormone response, light regulation and abiotic stress elements in the promoters of <i>HbBRI1s</i> and <i>HbBAK1s</i>. The results of tissue expression patterns indicate that <i>HbBRL1/2/3/4</i> and <i>HbBAK1a/b/c</i> are highly expressed in the flower, especially <i>HbBRL2-1</i>. The expression of <i>HbBRL3</i> is extremely high in the stem, and the expression of <i>HbBAK1d</i> is extremely high in the root. Expression profiles with different hormones show that HbBRI1 and HbBAK1 genes are extremely induced by different hormone stimulates. These results provide theoretical foundations for further research on the functions of BR receptors, especially in response to hormone signals in the rubber tree.
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