Genome-wide identification and expression analysis of the SOD gene family under biotic and abiotic stresses in sweet orange

Superoxide dismutase (SOD) protects plants from biotic and abiotic stress-induced reactive oxygen species toxicity and is extensively involved in plant growth and development. As the most widely cultivated and productive citrus fruit in the world, sweet oranges are susceptible to biotic and abiotic stresses during growth, affecting their yield and quality. However, the SOD gene family has not been identified in sweet oranges. Therefore, in this study, the sweet orange SOD gene family was systematically identified using bioinformatics methods, and a total of 15 sweet orange SOD (CsSOD) genes were identified and categorized into three subfamilies, Cu/Zn–SOD, Fe–SOD, and Mn–SOD, based on the results of the phylogenetic tree. Further analysis of gene structure and conserved motifs revealed that the motifs and exon and intron structures of CsSOD genes in the same subfamily were relatively identical, with only minor differences. In addition, we predicted hormone-related, light-response-related, and defense-related cis-acting elements in the promoters 2 kb upstream of the CsSOD genes. Transcriptome data analysis revealed that SOD genes were expressed under both abiotic and abiotic stresses, and the expression levels of some of the genes varied significantly. This study provides a basis for further understanding the biologic properties and functions of the SOD gene family in sweet oranges and provides a vital foundation for the study of sweet oranges under biotic and abiotic stresses.