Integrating Transcriptomics and Metabolomics to Characterize Metabolic Regulation to Elevated CO in Chlamydomonas Reinhardtii.

With atmospheric CO increasing, a large amount of CO is absorbed by oceans and lakes, which changes the carbonate system and affects the survival of aquatic plants, especially microalgae. The main aim of our study was to explore the responses of Chlamydomonas reinhardtii (Chlorophyceae) to elevated CO by combined transcriptome and metabolome analysis under three different scenarios: control (CK, 400 ppm), short-term elevated CO (ST, 1000 ppm), and long-term elevated CO (LT, 1000 ppm). The transcriptomic data showed moderate changes between ST and CK. However, metabolic analysis indicated that fatty acids (FAs) and partial amino acids (AAs) were increased under ST. There was a global downregulation of genes involved in photosynthesis, glycolysis, lipid metabolism, and nitrogen metabolism but increase in the TCA cycle and β-oxidation under LT. Integrated transcriptome and metabolome analyses demonstrated that the nutritional constituents (FAs, AAs) under LT were poor compared with CK, and most genes and metabolites involved in C and N metabolism were significantly downregulated. However, the growth and photosynthesis of cells under LT increased significantly. Thus, C. reinhardtii could form a specific adaptive evolution to elevated CO, affecting future biogeochemical cycles.