The roles of chloroplast membrane lipids in abiotic stress responses

Figures & data

Figure 1. ER-chloroplast interacts in the process of lipid biosynthesis, including: exporting fatty acids from plastids, thylakoid lipid biosynthesis. Acyl-ACP is released from the fatty acid synthase complex (FAS) and hydrolyzed into free fatty acids (FFA), using the FAX1/LACS mechanism to export FFA, reactivated into the acyl-CoA in the outer membrane of the chloroplast, through the Kennedy pathway or acyl.The editing approach incorporates acyl-CoA into the ER lipid. TGD regulates the transport of lipids (mainly PA) across the inner and outer chloroplast membranes into the chloroplast. MGDG is synthesized from chloroplast-derived lipids and ER-derived lipids, which can then be desaturated by chloroplast-specific FAD. The blue arrow shows the lipid assembly reaction of the plastid pathway, the red arrow shows the ER pathway reaction, and the yellow arrow shows the common reaction, mainly the biosynthesis of MGDG and DGDG. The biosynthesis of MGDG occurs on the surface of the inner envelope, and the biosynthesis of DGDG occurs on the cytoplasmic surface of the outer envelope. FADs fatty acid desaturases, DGD1 digalactosyldiacylglycerol synthase 1, MGD1 monogalactosyldiacylglycerol synthase 1, PAP phosphatidic acid phosphatase, LPAAT lyso-phosphatidic acid acyltransferase, GPAT glycerol-phosphate acyltransferase, DGAT diac glycerol acyltransferase, TGD trigalactosyldiacylglycerol, LACS long-chain acyl-CoA synthetases, FAX1 fatty acid export 1, PA phosphatidic acid, PC phosphatidylcholine, MGDG monogalactosyldiacylglycerol, DGDG digalactosyldiacylglycerol

Figure 2. In thylakoids, MGDG, DGDG, SQDG and PG are synthesized by PA through different pathways. MGDG is synthesized by MGD synthetase, which catalyzes the transfer of galactose from UDP-Gal to the DAG. DGD synthase transfers a second galactose from UDP-Gal to MGDG to form DGDG; MGDG synthesizes DGDG through DGD1/DGD2 pathway, and then forms TGDG from SFR2

Table 1. Typical functions of membrane lipids

Lipid species	Description	Related references
MGDG	In the mgd1 mutant, the electrical conductivity of the thylakoid membrane increased, thereby weakening the photoprotective effect of the thylakoid membrane.	100–102
DGDG	DGDG confers thermotolerance to plants due to its bilayer-stabilizing properties as demonstrated by the failure of DGDG-defi cient dgd1 mutant plants to adapt to high growth temperatures.	103,104
SQDG	SQDG is a negatively charged glycolipid, composed of more saturated fatty acids, and contains different numbers of eukaryotic and prokaryotic species according to plant species.	106–109
PG	PGs are the major phospholipid in thylakoid membranes of higher plants and can be used as a precursor of cardiolipins located on the inner mitochondrial membrane that are required for proper functioning of the oxidative phosphorylation enzymes.	115,118

Abbreviations: MGDG, monogalactosyldiacylglycerol; DGDG, digalactosyldiacylglycerol; SQDG, sulfoquinovosyldiacylglycerol; PG, phosphatidylglycerol.

Figure 3. (a) Fatty acid biosynthetic pathway and regulating mechanism of fatty acid desaturases in response to stress. (b) Under abiotic stress, the ω-3 fatty acid desaturase gene FAD3 catalyzes 18:2 to 18:3 in phospholipids, giving plants resistance to stress

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