Integrated physiological, transcriptomics and metabolomics analyses provide insights into thermal stress of razor clam, Sinonovacula constricta

Extreme high temperature is believed as a major inducer to summer mortality syndrome in molluscs, which frequently occurs and has caused serious economic losses. In this study, we elucidated the molecular differences of transcriptomic and metabolomics responses and investigated the mechanisms of response to heat stress in razor clam (Sinonovacula constricta) after exposure to 32 degrees C lasting for either 24 h or 15 d. Notably, protein processing in endoplasmic reticulum (ER) and glycerophospholipid pathway were obviously enriched, suggesting that maintaining ER and cell membrane homeostasis play an important role for razor clams to response to heat stress. After heat stress for 24 h, fatty acid synthesis-related genes, fasn, far1 and scd5, were repressed, and the contents of fumarate and citrate metabolites and the activities of SDH and CS enzymes in TCA cycle were significantly reduced. By contrast, T-SOD and CAT activities and MDA content were dramatically increased. After heat stress for 15 d, the lipid metabolism-related genes ppar alpha and plb1 were downregulated, and the SDH activity was remarkably decreased. Conversely, the expression of pck1 and odh were upregulated, indicating that heat stress may limit the aerobic capacities of the razor clams. Additionally, T-SOD activity was still higher than that of the control group, while CAT activity and MDA content decreased. These findings suggested that heat stress may inhibit the lipid metabolism and TCA cycle, activate oxidative stress and cause misfolded proteins accumulation which leads to ER stress. This study contributes to understand the potential metabolism mechanisms of S.constricta in response to heat stress.