GSE118760
Transcriptomic and lipidomic analysis of an EPA-containing Nannochloropsis sp. PJ12 in response to nitrogen deprivation
Oleaginous microalgae Nannochloropsis spp. are considered to be promissing species   for production of biofuels and biomaterials. Nevertheless, its biofuel production remains to  be economically unviable. Hence, further improvement of cultivation conditions and genetic  traits for high-lipid contents without affecting growth is required. To understand genes  involved in neutral lipid accumulation upon nitrogen deprivation (ND) in a novel isolate of  Nannochloropsis sp. PJ12, we performed comparative transcriptomic and lipidomic analyses  of cells under ND and NR (nitrogen replete) conditions. Transcriptomic profiling indicated  that, while enzymes involved in TCA cycle in PJ12 under ND condition were upregulated  compared to that under NR condition, those involved in Calvin cycle and glycolysis under  ND condition were downregulated, consistent with the observation that quantum yield was  reduced under ND condition. Furthermore, we showed that enzymes involved in fatty acid  synthesis and glycerolipid synthesis were downregulated but not b-oxidation. Lipidomic  profiling indicated that, while the level of neutral lipids in ND cells was increased compared  to that of NR cells, level of photosynthetic membrane-lipids DGDG and MGDG was  decreased. Taken together, our analysis indicated that TAG accumulation is attributed to the  modification of membrane lipids derived primarily from “prokaryotic” pathway and  secondarily from “eukaryotic” pathway based on the 16:X or 18:X fatty acid at the sn2  position of the glycerol backbone. We propose that two-phase (NR-ND) growth is ideal for  biomass and biofuel production because ND reduces cell growth rate due to the loss of  photosynthetic membrane and decreased quantum yield. Overall design: Examination of transcriptional profiling of PJ12 cells in response to nitrogen replete and nitrogen deprivation.