Integration of transcriptome and metabolome reveals tolerance mechanism to high salinity stress in Crassostrea hongkongensis

Crassostrea hongkongensis (C. hongkongensis) is an important economic species thriving in intertidal and estuarine areas, and suffers frequent salinity fluctuation. In this study, the transcriptomic and metabolomic were conjointly analyzed to reveal the tolerance mechanism of C. hongkongensis in response to high salinity stress. After high salinity stress at sub-lethal concentration (40 ‰) for 48 h, the enzyme activities of SOD, CAT, LZM, GSH-PX and AKP were measured to confirm that C. hongkongensis had activated the physiological stress reoponses. A total of 232 differentially expressed genes (DEGs) and 968 DEGs were identified after salinity stress for 6 h and 48 h, respectively. DEGs enriched pathways mainly included NOD-like receptor signaling pathway, oxytocin signaling pathway, pentose and glucuronate interconversions, NF-kappa B signaling pathway, apoptosis and so on. A total of 33 differential metabolites (DMs) and 61 DMs were identified in 6 h and 48 h salinity-stress groups. KEGG function analysis showed that DMs mainly involved in free amino acids metabolism, pentose and glucuronate interconversions, fatty acids biosynthesis, aminoacyl-tRNA biosynthesis, pantothenate and CoA biosynthesis and so on. Correlation analysis between DEGs and DMs found that the integrated regulatory network was involved in amino acid metabolism, aminoacyl-tRNA biosynthesis, fatty acid degradation, pyrimidine metabolism, etc. The data suggested that high salinity could cause stress response of C. hongkongensis by adjusting osmotic balance, carbohydrates and lipids metabolism and transfer systems. The study provided important information for understanding molecular mechanism of salinity tolerance in oysters.