Characterization of Chlamydomonas reinhardtii phosphatidylglycerophosphate synthase in Synechocystis sp. PCC 6803

Abstract

Phosphatidylglycerol (PG) is an indispensable phospholipid class with photosynthetic function in plants and cyanobacteria. However, its biosynthesis in eukaryotic green microalgae is poorly studied. Here, we report the isolation and characterization of two homologs (CrPGP1 and CrPGP2) of phosphatidylglycerophosphate synthase (PGPS), the rate-limiting enzyme in PG biosynthesis, in Chlamydomonas reinhardtii. Heterologous complementation of Synechocystis sp. PCC 6803 pgsA mutant by CrPGP1 and CrPGP2 rescued the PG-dependent growth phenotype, but the PG level and its fatty acid composition were not fully rescued in the complemented strains. As well, oxygen evolution activity was not fully recovered, although electron transport activity of photosystem II was restored to the wild-type level. Gene expression study of CrPGP1 and CrPGP2 in nutrient-starved C. reinhardtii showed differential response to phosphorus and nitrogen deficiency. Taken together, these results highlight the distinct and overlapping function of PGPS in cyanobacteria and eukaryotic algae.

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

“…PG is synthesized from PA through the action of enzymes including phosphatidylglycerophosphate synthase (PGPS). Two PGPS gene isoforms in C. reinhardtii are down-regulated during P starvation (Hung et al, 2015), presumably as part of the strategy to compensate for low P availability by reducing phospholipid biosynthesis (Riekhof et al, 2003). Thus, in the GPD3-OE cells, despite increased PA synthesis, if PGPS activity is repressed, PG content will not increase.…”

“…PG is thought to be mostly synthesized in the chloroplast from prokaryotic pathway PA, although additional synthesis in the ER cannot be discounted (Boudière et al, 2014;Li-Beisson et al, 2015). Indeed the localization of either PGPS isoform is unknown, with one predicted to be chloroplastic and the other nonchloroplastic (Hung et al, 2015;Li-Beisson et al, 2015). It is unclear whether the PG inhibition within the GPD3-OE lines is due to reduced chloroplastderived PG, perhaps due to up-regulated and overcompensated eukaryotic pathway activity or reduced ER-derived PG.…”

“…6). C. reinhardtii mutants that have lower PG content display reduced chlorophyll abundance, chlorophyll fluorescence, and PSII activity due to the absence of PSII core proteins, which can lead to reduced cell growth (Maroc et al, 1987;Pineau et al, 2004;Hung et al, 2015).…”

The lipid biochemistry of eukaryotic algae

“…Putative genes for phosphatidate cytidylyltransferase, phosphatidylglycerolphosphate (PGP) synthase and phosphatidylinositol synthase were described in C. reinhardtii [56,251] and one for phosphatidylglycerol synthase noted in P. tricornutum [37] but, until recently, there has been a dearth of work on the synthesis of such anionic phospholipids in eukaryotic algae except for indirect studies on inoculum size in altering phosphoglyceride profiling [272] and the work on both PGP synthase and PGP phosphatase 1 from C. reinhardtii [273,274]. Two homologues of PGP synthase (CrPGP1 and CrPGP2) were isolated and characterised from C. reinhardtii [273]. Their function was demonstrated by complementation of a mutant of Synechocystis sp.…”

Isolation and characterization of a mutant defective in triacylglycerol accumulation in nitrogen-starved Chlamydomonas reinhardtii

“…ChlamydomonasResource Center (St. Paul, MN) and used as a wild type.Cells were grown in Tris-acetate-phosphate (TAP) medium (Gorman and Levine, 1965)or high salt (HS) medium (Sueoka, 1960)supplemented with 50 mg L -1 of arginine with air bubbling under 50~60µmol continuous white light at 22°C by stirringat 200rpm. C. reinhardtii strain CC-4351 transformed with empty pChlamiRNA2 plasmid (Molnar et al, 2009) was used as empty vector control strain (Hung et al, 2015). Cell numberwas counted by automatic cell counter (Cellometer ® AutoT4, Nexcelom Bioscience, Lawrence, MA).…”