Genome-wide identification and abiotic stress response analysis of the <i>SUMO</i> family in alfalfa ( <i>Medicago sativa</i> L.)

SUMOylation is a well-conserved post-translational modification that is essential for modulating plant adaptation to various abiotic stresses. Although the functions of small ubiquitin-like modifier (SUMO) genes have been reported in various plant species, systematic studies focusing on the SUMO gene family members in alfalfa remain limited. In this study, we identified 49 MsSUMO genes from the alfalfa genome using bioinformatics approaches, and conducted comprehensive analyses of their phylogenetic relationships, structural features, cis-regulatory elements, and expression patterns. Most MsSUMO genes were predicted to localize in the nucleus and cytoplasm, consistent with their roles in transcriptional regulation and protein modification. Phylogenetic analysis grouped MsSUMO, soybean and Arabidopsis SUMO genes into seven subfamilies, which exhibited both high homology and species-specific divergence, suggesting functional differentiation during evolution. Conserved motif and domain analyses revealed strong structural consistency among MsSUMO members, with relatively simple gene architectures. In total, 59 types of cis-elements were detected in the promoter regions, playing crucial roles in plant growth, light signaling, and responses to biotic and abiotic stresses. Abscisic acid-responsive elements (ABREs) were the most abundant, implying that this gene family may serve key functions in stress regulation via the abscisic acid (ABA) signal pathway. Protein interaction network analysis indicated that MsSUMO members cooperate with core enzymes to modulate downstream stress-responsive targets. Transcriptome and real-time quantitative polymerase chain reaction (RT-qPCR) results showed that eight MsSUMO genes exhibited significant expression responses to salt, drought, and waterlogging stresses. Remarkably, six genes consistently exhibited upregulation across all three stress conditions. This observation underscores their potential as pivotal players in abiotic stress tolerance and identifies them as promising candidates for subsequent functional characterization.