Transcriptomic analysis of a cold‐resistant Nordic microalga: unraveling the mechanisms underlying adaptation to low temperatures

Abstract Cold stress imposes a great physiological impact on most photosynthetic organisms. The acclimation to cold is very poorly studied in microalgae, even though understanding the molecular mechanisms underlying their cold tolerance has implications for biotechnological applications, such as the development of cold‐tolerant strains for industrial purposes. Scenedesmus sp . B2‐2 is a Nordic strain of green freshwater microalgae that thrives in cold conditions. Here, we analyzed transcriptomic changes of B2‐2 when exposed to the cold (5°C) and compared it to a control grown at 25°C. The aim was to understand more about the mechanisms underlying B2‐2's adaptation to low temperatures. We studied differentially expressed genes (DEGs) related to lipid synthesis, carbon metabolism and photosynthesis. Scenedesmus sp . B2‐2 produced more lipids when exposed to cold conditions and did not reduce its carbon metabolism or photosynthetic processes. 24 putative cold‐responsive genes were found to be non‐responsive in Scenedesmus sp . B2‐2 when grown at 5°C. These genes could serve as targets for genetic engineering to enhance cold tolerance in algal strains used in biotechnology. We also studied B2‐2´s cell wall changes in response to cold by measuring cell wall thickness at 1, 4, 12, 24, 48, 72, 120 and 240 hours of cold exposure and correlating the results to the transcriptomic data. The results show that the cell wall thickens with increased duration of cold exposure. Several glycosyltransferases were found to be significantly up‐regulated throughout cold exposure and may play a role in cell wall thickening.