Genome-Wide Identification of the Soybean GH5 Gene Family and Functional Analysis of GmGH5-22 in Salt Tolerance

Plant GH5 family genes function in both cell wall biosynthesis and stress responses. However, comprehensive studies on GH5 genes in the soybean remain limited. Here, we identified 28 GmGH5 genes from the soybean genome. Phylogenetic analysis assigned these genes to three subfamilies (I–III), with no representatives in subfamily IV. The GmGH5 family harbors 15 conserved motifs, which are largely similar within subfamilies but differ across subfamilies. Additionally, exon–intron structures (2–7 introns) exhibit clade-specific patterns, with members within the same clade sharing similar intron numbers and lengths, whereas distinct clades show some variation. The promoter regions of GmGH5 genes contained various cis-acting regulatory elements associated with stress responses and developmental processes. Transcriptome-based expression profiling revealed distinct tissue-specific expression patterns of GmGH5 genes. RT-qPCR further confirmed their differential expression under salt, alkaline, cold, and drought stresses, especially a significant increase in GmGH5-22 expression under salt stress (approximately 22-fold at 6 h, **** p < 0.0001). Furthermore, GmGH5-22 was highly expressed in roots, and transient expression in tobacco leaves showed its peripheral localization, which aligns with its predicted extracellular localization, suggesting that GmGH5-22 is highly likely localized to the cell wall. Overexpression of GmGH5-22 in soybean hairy roots significantly improved tolerance to salt stress. These findings establish a foundation for functional characterization of GmGH5 genes and provide viable targets for molecular breeding to enhance salt tolerance in soybeans.