Two Glycerol-3-Phosphate Dehydrogenases from Chlamydomonas Have Distinct Roles in Lipid Metabolism

Abstract

The metabolism of glycerol-3-phosphate (G3P) is important for environmental stress responses by eukaryotic microalgae. G3P is an essential precursor for glycerolipid synthesis and the accumulation of triacylglycerol (TAG) in response to nutrient starvation. G3P dehydrogenase (GPDH) mediates G3P synthesis, but the roles of specific GPDH isoforms are currently poorly understood. Of the five GPDH enzymes in the model alga Chlamydomonas reinhardtii, GPD2 and GPD3 were shown to be induced by nutrient starvation and/or salt stress. Heterologous expression of GPD2, a putative chloroplastic GPDH, and GPD3, a putative cytosolic GPDH, in a yeast gpd1D mutant demonstrated the functionality of both enzymes. C. reinhardtii knockdown mutants for GPD2 and GPD3 showed no difference in growth but displayed significant reduction in TAG concentration compared with the wild type in response to phosphorus or nitrogen starvation. Overexpression of GPD2 and GPD3 in C. reinhardtii gave distinct phenotypes. GPD2 overexpression lines showed only subtle metabolic phenotypes and no significant alteration in growth. In contrast, GPD3 overexpression lines displayed significantly inhibited growth and chlorophyll concentration, reduced glycerol concentration, and changes to lipid composition compared with the wild type, including increased abundance of phosphatidic acids but reduced abundance of diglycerides, triglycerides, and phosphatidylglycerol lipids. This may indicate a block in the downstream glycerolipid metabolism pathway in GPD3 overexpression lines. Thus, lipid engineering by GPDH modification may depend on the activities of other downstream enzyme steps. These results also suggest that GPD2 and GPD3 GPDH isoforms are important for nutrient starvation-induced TAG accumulation but have distinct metabolic functions.

Novel insights into salinity-induced lipogenesis and carotenogenesis in the oleaginous astaxanthin-producing alga Chromochloris zofingiensis: a multi-omics study

“…This is generally consistent with the results under ND conditions that Cz04g17090 was up-regulated [15], indicative of its critical role in G3P production for glycerolipid assembly. Interestingly, in C. reinhardtii, the chloroplastic GPDH genes rather than the cytosolic ones were up-regulated by ND or salt stress, and played a role in TAG accumulation [98,104]. This may partially explain that under TAG induction conditions, C. zofingiensis activates transcriptional up-regulation of the extrachloroplastic GPAT (Fig.…”

Multiomics analysis reveals a distinct mechanism of oleaginousness in the emerging model alga Chromochloris zofingiensis

“…and one LCAS (Cz11g20120) were upregulated substantially (Table S5), which are potential targets to enhance the production of acyl‐CoAs ready for TAG assembly. In addition to acyl‐CoAs, G3P is the other precursor providing the glycerol backbone for TAG assembly, which is derived mainly from DHAP catalyzed by GPDH (Yao et al ., ; Driver et al ., ). One of the four GPDH genes in C. zofingiensis , Cz04g17090, was considerably upregulated by ND and correlated well with TAG accumulation (Table S11), therefore representing a promising engineering target.…”

Chlorella vulgaris genome assembly and annotation reveals the molecular basis for metabolic acclimation to high light conditions

“…In addition to de novo fatty acid biosynthesis, enzymes involved in the supply of glycerol backbones and TAG packaging were upregulated in HL. Two G3P dehydrogenase (GPD) enzymes were indeed identified in the C. vulgaris 211/11P genome, but only the non‐chloroplastic GPD2 was upregulated in HL: this enzyme has been reported in C. reinhardtii to be involved in supplying G3P for TAG synthesis and accumulation in nutrient starvation (Driver et al ., ).…”