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

## TL;DR

This study explores the SOD gene family in three Hyotissa bivalve species, revealing diverse and specialized genes that may help them survive in harsh reef environments.

## Contribution

The study provides the first comprehensive transcriptomic and comparative analysis of SOD genes in Hyotissa species.

## Key findings

- 46 SOD genes were identified, showing both conserved and diversified features.
- Specialized SODs like Dominin and CSRPs suggest functional divergence and adaptation.
- The SOD family in Hyotissa appears to have evolved to cope with high-oxygen and high-ultraviolet reef conditions.

## Abstract

The marine bivalves of the genus Hyotissa (family Gryphaeidae) are important for ocean ecosystems and fisheries; however, their molecular biology information is notably scarce. Our study aimed to specifically explore crucial defense genes called superoxide dismutases (SODs), which act as the body’s natural defenders against cellular damage. We discovered 46 diverse SOD genes in three Hyotissa species. Our analysis revealed that these genes possess both ancient, conserved features and newer, diversified characteristics. Intriguingly, we found specialized SODs like Dominin and copper-only SOD repeat proteins (CSRPs), exhibiting structural changes hinting at new roles. These variations suggest Hyotissa’s protective genes have adapted to perform various tasks, potentially enabling them to thrive in demanding reef environments characterized by high ultraviolet radiation and high oxygen levels. This study provides foundational transcriptomic resources for Hyotissa and offers new insights into the evolution and environmental adaptation of SOD genes in marine bivalves.

The genus Hyotissa (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 Hyotissa species—H. sinensis, H. inaequivalvis, and Hyotissa 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 Hyotissa 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 Hyotissa and offers new insights into the evolution and environmental adaptation of SOD genes in marine bivalves.