Examination of carbohydrate and lipid metabolic changes during Haematococcus pluvialis non-motile cell germination using transcriptome analysis

During the complex Haematococcus pluvialis life cycle, germination from non-motile cells to motile cells is the key stage for cell recovery from resting spores. Three phases can be recognized: first, repeated mitotic events; next, cytokinesis to form the zoospore; and finally, a fast release of motile cells. After HiSeq 2000 sequencing of RNA collected at four time points during non-motile cell germination, a total of 2202 differentially expressed genes (DEGs) were identified. In the expression profiles, there is a consistent increase in the expression level of α-amylase and ACAA1 in the entire process, indicating starch and lipid mobilization. In phase 1, two down-regulated genes (fructose-1, 6-bisphosphate aldolase (FBA) and pyruvate kinase (PK)) of glycolysis limited the provision of acetyl-CoA for the TCA cycle, which could be compensated by fatty acid degradation (up-regulation of ACAA1) in the glyoxysome. In phase 2, nine and eight up-regulated enzymes of carbohydrate (glycolysis, TCA cycle, and pentose phosphate pathway) and lipid (fatty acid synthesis and degradation) metabolism, respectively, would increase the metabolic rate and come into a balance between production and consumption of starch and lipid. Till phase 3, the expression of the vast majority of carbohydrate metabolism-related DEGs remained high, while lipid metabolism did not. This suggested that the carbon flux centered on carbohydrate metabolism in this phase. In addition, several isozymes of FBA, GAPDH, PK, and so on were separated by SMART analysis and are postulated to serve different actions during H. pluvialis non-motile cell germination.