The Transcriptomic Responses of the Ark Shell, Anadara Broughtonii, to Sulfide and Hypoxia Exposure

Sulfide and hypoxia threaten marine organisms in various ways. Anadara broughtonii, a commercial marine bivalve in China which has great potential exposure to sulfide and hypoxia, was selected to test the responses to these stresses. Digital gene expression profile (DGE) analysis was performed on the juveniles' gills after exposed to normal condition (CG group), hypoxia (LO group), and low/high concentration of sulfide (LS/HS group, administered in hypoxia), respectively, using RNA-seq technology. A total of over 30 million clean reads were filtered from each DGE library and over 90% of them were annotated successfully. In total, 774 significant differentially expressed genes (DEGs) were detected and assigned to Gene ontology (GO) classification and KEGG Pathway enrichment analysis. The results show that many of the upregulated DEGs are related to hemoglobin, immunology, and stress responding. In the stressed A. broughtonii, cytochrome P450 and phosphoenolpyruvate carboxykinase may stimulate the glycolysis process to reduce oxygen consumption; Aminoacyl-tRNA synthetases, heat shock protein and protein disulfide isomerase probably help to maintain the genome integrity; Baculoviral IAP repeat-containing protein 2/3, mitogen-activated protein kinase and tumor necrosis factor pathways were probably responsible for protein repair, proteolysis, apoptosis and immune responses to high concentration of sulfide. Combined challenges also induced alternative oxidase and sushi repeat-containing protein, which have indistinct but probably indispensable function in invertebrates. For the first time, comprehensive transcriptome information on A. broughtonii in response to sulfide and hypoxia were provided. Our research offers new insights into the molecular mechanism behind the resistance of shellfish to sulfide and hypoxia.