Comparative transcriptome analyses unravel the response to acute thermal stress in the razor clam, Sinonovacula constricta

The razor clam, Sinonovacula constricta, must have acquired adaptive mechanisms to defense thermal pressure during evolution as it's an eurythermal bivalve. However, the specific mechanisms remain unclear. To identify thermal responsive genes and unravel adaptive mechanisms, the clams were subjected to acute thermal stress from 21 degrees C to 32 degrees C for 24 h. The transcriptomic profilings of gills and hepatopancreas from control and treatment groups were investigated. A total of 786 differentially expressed genes (DEGs) were identified in the hepatopancreas between both groups while 556 DEGs were identified in the gills. GO and KEGG analysis showed that these DEGs were significantly enriched in protein homeostasis, metabolisms, immune response, antioxidant response and cytoskeletal organization processes. Protein processing in endoplasmic reticulum was most enriched in the gills. Lipid metabolism pathway was mainly repressed in the hepatopancreas. Antigen processing and presentation and NOD-like receptor (NLR) signaling pathways were enriched in both tissues while C-type lectins (CTLs) and allograft inflammatory factor (AIF) were more significantly down-regulated in the hepatopancreas (P < 0.05). Besides, the cytoskeletal structure related genes showed opposite expression pattern in the gills and hepatopancreas after thermal stress, such as tubulin-related genes were up-regulated in the gills, while fibrillins (FBNs) were down-regulated in the hepatopancreas. These findings suggested gills and hepatopancreas have specific functions to thermal stress. Our results indicated that multiple-biological process adjustments have occurred in the razor clam after heat stress. This study will contribute to understanding the molecular adaptive mechanism to heat stress and provide candidate genes for genetic breeding with thermal resistant trait.