The integrated analysis of physiology and transcriptomes provide insights into the short- and long-term salinity adaptation of the diatom (Thalassiosira profunda)

Global climate change has resulted in alterations in salinity in both marine and freshwater environments, posing severe challenges to the survival of diatoms. Elucidating the physiological responses and adaptive mechanisms of diatoms, particularly those inhabiting estuarine regions, to salinity fluctuations holds significant ecological implications for sustaining primary productivity in estuarine ecosystems and preserving biodiversity in coastal zones. In this study, we investigated the metabolic adaptation of Thalassiosira profunda to salinity over short term (7 days) and long term (2 years) periods at two salinity levels (30 PSU and 15 PSU) by analyzing physiological changes and transcriptomics. The results demonstrated that T. profunda responded to oxidative damage by increasing synthesis of polysaccharides, proteins and enhancing antioxidant enzyme activities when exposed to low salinity. T. profunda upregulated photosynthesis to obtain additional energy for oxidative damage repair. We observed that short-term salinity change resulted in a reprogramming of cellular nitrate metabolism, TCA cycle and fatty acid metabolism. The upregulation of mitogen-activated protein kinase signaling pathway enhanced intrinsic cellular catalase activity levels, which might be crucial for alleviating photosystem damage in long-term low salinity adaptation.