Transcriptome Assembly and Comparative Analysis of the Superoxide Dismutase (SOD) Gene Family in Three Hyotissa Species

The genus <i>Hyotissa</i> (family Gryphaeidae) comprises ecologically and economically important marine bivalves, yet their molecular biology remains poorly characterized. This study presents de novo transcriptome sequencing of three <i>Hyotissa</i> species-<i>H. sinensis</i>, <i>H. inaequivalvis</i>, and <i>Hyotissa</i> sp.-to systematically identify and characterize the superoxide dismutase (SOD) gene family, a crucial component of the antioxidant defense system. We identified 46 SOD genes, including both Cu/Zn-SOD and Fe/Mn-SOD types, which exhibited considerable variation in molecular properties, domain architecture, and potential phosphorylation sites. Phylogenetic analysis revealed both evolutionary conservation and diversification of SODs across species. Notably, we identified homologs of two specialized SOD types: Dominin, which showed mutations in metal-binding sites suggestive of functional divergence, and copper-only SOD repeat proteins (CSRPs), which retained copper-binding residues but lost zinc-binding capacity. These findings suggest that the SOD family in <i>Hyotissa</i> has undergone significant functional diversification, potentially as an adaptive response to their high-oxygen, high-ultraviolet reef habitats. This study provides foundational transcriptomic resources for <i>Hyotissa</i> and offers new insights into the evolution and environmental adaptation of SOD genes in marine bivalves.