Transcriptome analysis reveals the molecular mechanism of differences in growth between photoautotrophy and heterotrophy in Chlamydomonas reinhardtii

Abstract

Background Chlamydomonas reinhardtii can grow photoautotrophically and heterotrophically, and is the typical model species for heterotrophy increasingly cultured in commercial cultivation. By observing their growth changes, transcriptomic analysis and molecular regulation, we investigated the molecular mechanism of differences in growth from photoautotrophy 12h (P12h) to heterotrophy 12h (H12h). Results We observed changes in the cell numbers, OD750, Fv/Fm, and total chlorophyll content of photoautotrophy and heterotrophy during 10 days and they were significantly different. These indicators were further analyzed between photoautotrophy 12h (P12h) and heterotrophy 12h (H12h), and the P12h group was significantly higher than the H12h group. The transcriptome data demonstrated that a total of 2,970 differentially expressed genes (DEGs) were identified between the P12h and H12h groups. There were 10 DEGs involved in the photosynthesis and carbon fixation metabolic pathway, 18 DEGs involved in the glycolysis and the TCA cycle metabolic pathway, 8 DEGs related to the pyruvate metabolic pathway, and 17 DEGs related to the oxidative phosphorylation. To explore the relationship between DEGs and the major metabolic pathways, the relative expression levels of marker genes and key enzyme activities were examined. The relative expression levels of MDH, SDH, ATPase and SSS were increased significantly from P12h and H12h. NAD-MDH and SDH activity of the H12h group was significantly higher than the P12h group. Conclusions Our study exhibited characteristics of early fermentation in Chlamydomonas reinhardtii. Based on analysis of transcriptome and biochemical, we speculated the nutrient and energy metabolism models and partly elucidated the molecular mechanism of both the heterotrophic and autotrophic Chlamydomonas reinhardtii. Our study provides preliminary evidence for the differences in the growth of photoautotrophy and heterotrophy in algae.