Genome-wide evolutionary and comparative analysis of superoxide dismutase gene family in three bladed Bangiales species

As a key component of the plant antioxidant enzymatic system, superoxide dismutase (SOD) can efficiently protect cells from oxidative stress and maintain redox homeostasis. Currently, there are few studies related to SOD genes in various taxa of algae, and the specific functions and evolutionary patterns of these family members remain unclear. In this study, comprehensively evolutionary analysis of SOD gene family in the bladed Bangiales was carried out. A total of 9, 10, and 12 SOD genes were identified from three species of Pophyra umbilicalis, Pyropia haitanensis, and Pyropia yezoensis, respectively. Based on phylogenetic analysis, SOD gene members within the same subfamily exhibited similar motif patterns as well as conserved domains, which could be attribute to Cu/Zn-SOD and Fe/Mn-SOD. The promoter regions of SOD genes were rich in hormone-responsive, stress-responsive, and growth cis-acting elements, with variations and similarities observed among different species of other red algae and subfamilies. According to subcellular location prediction, it is suggested that Cu/Zn-SOD was predominantly located in chloroplasts, while Fe/Mn-SOD was primarily located in mitochondria. Also, the two subfamilies differed significantly in the two-/three-dimensional protein structures. In terms of gene evolution, the strongest collinearity relationship was shown between Pyropia haitanensis and Pyropia yezoensis, with all the 1:1 orthologous gene pair being subjected to a purifying selection (Ka/Ks<1, Ka: non-synonymy rate; Ks: synonymy rate). Moreover, 12 SOD genes underwent positive selection during the evolutionary process. Furthermore, gene expression analysis based on transcriptomic data from Pyropia haitanensis showed that the expression patterns of SOD genes varied under different stress conditions. Together, this study revealed the evolutionary pattern of SOD genes in three bladed Bangiales species, which will lay the foundation for subsequent studies on the function of SOD genes.