Abstract:Brassinosteroids ( BRs ) play an important role in plant growth and development, and Brassinosteroid insensive 1 ( BRI1 ) plays a major role in BR signaling pathway. Soybean ( Glycine max ( L. ) Merr. ) is an important food and economic crop in the world. Unlike other crops, soybean can form a symbiotic relationship with rhizobia for biological nitrogen fixation. However, the function of GmBRI1 in regulating soybean growth and symbiotic nitrogen fixation is still unclear. Therefore, identification and analysis of the characteristics and functions of GmBRI1 gene family members are crucial for revealing the unique role of BR signaling in soybean growth and development. In this study, six GmBRI1 family genes were identified by bioinformatics methods in soybean genome, which were non-uniformly distributed on four chromosomes of soybean. The number of amino acids was between 1136-1211 aa, and the proportion of leucine was the highest, all of which were acidic and stable proteins. Phylogenetic analysis showed that the GmBRI1 gene family could be divided into three subfamilies. The gene structure and conserved motif distribution of the same subfamily are highly similar. Synteny analysis showed that fragment replication was the main reason for the expansion of GmBRI1 gene family. The promoter of the GmBRI1 family gene contains abundant cis-acting elements that regulate soybean light response, hormone response, stress response, and growth and development. The number of potential phosphorylation sites of GmBRI1 family genes was between 111-132. The protein interaction network predicted that there were 19 proteins interacting with GmBRI1 and 4 proteins directly binding, which participate in the regulation of various biological processes in the BR signal transduction pathway by interacting with various proteins. The GmBRI1 family genes are expressed in both roots and nodules, and GmBRI1a, GmBRI1b, GmBRL1a and GmBRL1b genes are down-regulated after rhizobia infection. This study provides a new theoretical basis for the functional study of soybean GmBRI1 family genes, and proves that they respond in the early stage of rhizobium infection, which provides basic information for further understanding the function and molecular mechanism of GmBRI1 gene family in soybean symbiotic nodulation.