Genome-Wide Characterization of the GmCOPT Family and Its Salt-Responsive Expression Patterns in Soybean

Background: Copper transporters (COPTs) are essential for maintaining copper homeostasis in plants, a process critical for growth, development, and stress adaptation. However, the soybean GmCOPT family remains poorly characterized. Methods: In this study, we performed a genome-wide identification of COPT genes in soybean (Glycine max), conducted phylogenetic, collinearity, and evolutionary analyses, predicted protein motifs, structures, and promoter cis-regulatory elements, and analyzed the expression profiles of the GmCOPT family. Results: We identified ten GmCOPT genes. Phylogenetic analysis of COPT proteins across five plant species revealed that soybean COPTs are more closely related to those from Medicago truncatula. Collinearity analysis suggested that segmental duplication is the primary driver of GmCOPT family expansion, and all duplicated gene pairs exhibited Ka/Ks ratios below 1, indicating purifying selection. Expression profiling revealed tissue-preferential patterns among GmCOPT genes. The presence of ABRE, MBS, and LTR cis-acting regulatory elements in the promoter regions of GmCOPTs suggests their potential involvement in abiotic stress responses. RT-qPCR validation demonstrated that GmCOPT genes responded differentially to salt stress in soybean roots and leaves, with some significantly repressed and others markedly induced. Notably, GmCOPT7 and GmCOPT8 were significantly induced in both tissues in response to salt stress. Conclusions: These findings suggest that GmCOPT genes have undergone duplication-driven expansion and functional diversification, with different expression patterns and salt-inducible responses. This work provides candidate genes for future functional investigations into the roles of GmCOPT genes in abiotic stress tolerance in soybean.