Genome-Wide Characterization of the Soybean DUF966 Gene Family Reveals Tissue- and Cultivar-Dependent Transcript Abundance After Drought Adaptation

Background/Objectives: Proteins containing the domain of unknown function 966 (DUF966) have been implicated in plant development and environmental responses, but the diversity of the soybean DUF966 gene family and its tissue-specific transcript abundance under prolonged drought remain insufficiently characterized. This study aimed to characterize the GmDUF966 gene family and examine transcript abundance of its members after prolonged drought treatment. Methods: Comparative genomic, phylogenetic, conserved motif, gene structure, and promoter cis-element analyses were conducted to characterize the GmDUF966 family. Public transcriptomic datasets were examined to assess tissue-specific expression patterns. Transcript abundance after 15 d of drought treatment was evaluated in roots and leaves of five soybean cultivars, alongside physiological measurements of lipid peroxidation, proline accumulation, antioxidant enzyme activities, and water-soluble protein content. Results: Twelve GmDUF966 genes were identified across eight soybean chromosomes and classified into three phylogenetic groups. Their predicted proteins ranged from 267 to 538 amino acids and exhibited hydrophobic characteristics. Conserved motifs and gene structures generally corresponded to phylogenetic relationships, while promoter analyses revealed putative hormone- and stress-responsive cis-elements. Under drought treatment, root expression of GmDUF966-7 increased in all five cultivars. GmDUF966-9 showed pronounced root expression increases in V4 and V5, with log2 fold changes of 8.46 and 7.69, respectively. Leaf expression was predominantly reduced, while physiological responses varied across cultivars and tissues. Conclusions: Soybean GmDUF966 genes exhibit conserved structural features and tissue-dependent drought-associated expression patterns. GmDUF966-7 and GmDUF966-9 showed the clearest root transcript differences after prolonged drought and may merit functional testing. Further experimental validation is required to establish their roles in drought tolerance.