Genome-Wide Evolution and Comparative Analysis of Superoxide Dismutase Gene Family in Cucurbitaceae and Expression Analysis of Lagenaria siceraria Under Multiple Abiotic Stresses

Superoxide dismutase (SOD) is an important enzyme that serves as the first line of defense in the plant antioxidant system and removes reactive oxygen species (ROS) under adverse conditions. The SOD protein family is widely distributed in the plant kingdom and plays a significant role in plant growth and development. However, the comprehensive analysis of the SOD gene family has not been conducted in Cucurbitaceae. Subsequently, 43 SOD genes were identified from Cucurbitaceae species [Citrullus lanatus (watermelon), Cucurbita pepo (zucchini), Cucumis sativus (cucumber), Lagenaria siceraria (bottle gourd), Cucumis melo (melon)]. According to evolutionary analysis, SOD genes were divided into eight subfamilies (I, II, III, IV, V, VI, VII, VIII). The gene structure analysis exhibited that the SOD gene family had comparatively preserved exon/intron assembly and motif as well. Phylogenetic and structural analysis revealed the functional divergence of Cucurbitaceae SOD gene family. Furthermore, microRNAs 6 miRNAs were predicted targeting 3 LsiSOD genes. Gene ontology annotation outcomes confirm the role of LsiSODs under different stress stimuli, cellular oxidant detoxification processes, metal ion binding activities, SOD activity, and different cellular components. Promoter regions of the SOD family revealed that most cis-elements were involved in plant development, stress response, and plant hormones. Evaluation of the gene expression showed that most SOD genes were expressed in different tissues (root, flower, fruit, stem, and leaf). Finally, the expression profiles of eight LsiSOD genes analyzed by qRT-PCR suggested that these genetic reserves responded to drought, saline, heat, and cold stress. These findings laid the foundation for further study of the role of the SOD gene family in Cucurbitaceae. Also, they provided the potential for its use in the genetic improvement of Cucurbitaceae.