Molecular mechanisms affecting the difference in salinity adaptability between juvenile and adult Hong Kong oysters

Abstract

The Hong Kong oyster (Crassostrea hongkongensis) lives in the brackish waters of estuaries in the intertidal zone and has a high resistance to low levels of salinity, but low resistance to higher levels. Juveniles are more sensitive to high levels of salinity than adults. To better understand the mechanisms underlying these differences, we performed a high-salinity stress analysis of juvenile and adult Hong Kong oysters. Trait analysis between groups showed that Na+-K+-ATPase activity, T-AOC, betaine, taurine and glycogen content of the high-salinity group were almost all higher than that of the control group at 8 h under high-salt stress, but lower than that of the control group at 96 h. The differences are more significant in Adult population. The results indicate that these indexes are related to the salinity adaptability of oysters. Enrichment analysis and protein-protein interaction (PPI) network analysis of the differentially expressed genes (DEGs) screened from transcriptomic data showed that their functions were mainly related to the oxidation-reduction process, immune response, protein ubiquitination and ATP synthesis. Furthermore, a weighted gene co-expression network analysis (WGCNA) of all samples showed that the hub gene functions were mainly associated with the oxidation-reduction process and immune response. These results indicate that immune response-related and antioxidant genes play key roles in the adaptability of Hong Kong oysters to high salinity. This study provides new insights and enriches our current understanding of the salinity adaptation mechanisms in oysters.