Abstract: To clarify the basic properties of the dehydroascorbate reductase (DHAR) gene in Hami melon and its expression level during cold stress, we investigated the basic information, multiple sequence alignment, phylogenetic relationship, collinearity and domain characteristics of two DHAR genes, protein three-dimensional (3D) models and protein-protein interaction, as well as ascorbic acid (AsA) contents, DHAR activities and DHAR gene expression levels under cold stress, and we performed gene set enrichment analysis (GSEA). The results showed that the lengths of the proteins encoded by the two CmDHAR genes consisted of 297 and 206 amino acids, respectively. Their isoelectric points were 8.67 and 5.99, respectively. Their molecular masses were 33 082.9 and 22 891.6 Da, respectively. Multiple sequence alignment analysis showed that the CmDHAR genes had a highly conserved glutathione S-transferase (GST) N-terminal functional domain. Gene structure analysis indicated that CmDHAR contained six exons, six conserved motifs and three types of cis-acting elements. Collinearity analysis indicated that Hami melon was evolutionarily closer to zucchini, winter squash and pumpkin. The 3D models revealed that the secondary structure of CmDHAR2 mainly included α-helix, random coil, extended strand and β-turn. Protein-protein interaction analysis showed that CmDHAR family members were closely related to other GST family members. The AsA content, DHAR activity and CmDHAR gene expression level in the cold-tolerant cultivar “Jiashi-310” (JS) were significantly higher than those in the cold-sensitive cultivar “Golden Empress-308” (GE) under cold stress. GSEA results revealed that the CmDHAR genes participated in the biological processes of ‘structural molecule activity’, ‘macromolecular complex’, ‘membrane-enclosed lumen’ and ‘antioxidant activity’. This study has proved that the CmDHAR genes play an important role in the resistance of Hami melon to cold stress.

Key words: Hami melon; glutathione S-transferase; dehydroascorbate reductase; cold stress