Dual Role for Phospholipid:Diacylglycerol Acyltransferase: Enhancing Fatty Acid Synthesis and Diverting Fatty Acids from Membrane Lipids to Triacylglycerol in Arabidopsis Leaves

Biosciences Department, Brookhaven National Laboratory, Upton, New York 11973.
The Plant Cell (Impact Factor: 9.34). 09/2013; 25(9). DOI: 10.1105/tpc.113.117358
Source: PubMed


There is growing interest in engineering green biomass to expand the production of plant oils as feed and biofuels. Here, we show that PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) is a critical enzyme involved in triacylglycerol (TAG) synthesis in leaves. Overexpression of PDAT1 increases leaf TAG accumulation, leading to oil droplet overexpansion through fusion. Ectopic expression of oleosin promotes the clustering of small oil droplets. Coexpression of PDAT1 with oleosin boosts leaf TAG content by up to 6.4% of the dry weight without affecting membrane lipid composition and plant growth. PDAT1 overexpression stimulates fatty acid synthesis (FAS) and increases fatty acid flux toward the prokaryotic glycerolipid pathway. In the trigalactosyldiacylglycerol1-1 mutant, which is defective in eukaryotic thylakoid lipid synthesis, the combined overexpression of PDAT1 with oleosin increases leaf TAG content to 8.6% of the dry weight and total leaf lipid by fourfold. In the plastidic glycerol-3-phosphate acyltransferase1 mutant, which is defective in the prokaryotic glycerolipid pathway, PDAT1 overexpression enhances TAG content at the expense of thylakoid membrane lipids, leading to defects in chloroplast division and thylakoid biogenesis. Collectively, these results reveal a dual role for PDAT1 in enhancing fatty acid and TAG synthesis in leaves and suggest that increasing FAS is the key to engineering high levels of TAG accumulation in green biomass.

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Available from: Xuebin Zhang, Jul 14, 2014
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    • "and free fatty acids ( FFAs ) in the presence of limiting amounts of divalent cations ( Sakaki et al . , 1990b ) . Because fatty acid synthesis is markedly enhanced in both tgd1 - 1 ( Fan et al . , 2013a ) and tgd5 mutants , and the majority of the de novo - synthesized fatty acids are exported into the cytosol to enter the b - oxidation pathway ( Fan et al . , 2013b ) , an attractive possibility is that GGGT is activated due to the passage of increased amounts of FFAs through the outer envelope membrane . In support of this , both oligogalactolipids and FFAs have also been reported to accumulate in isolated chloroplasts following prolonged incubation ( Ongun and Mudd , 1968 ; Heemskerk et al . , 19"
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    ABSTRACT: The biogenesis of photosynthetic membranes in the plastids of higher plants requires an extensive supply of lipid precursors from the endoplasmic reticulum (ER). Four TRIGALACTOSYLDIACYLGLYCEROL (TGD) proteins (TGD1,2,3,4) have thus far been implicated in this lipid transfer process. While TGD1, TGD2, and TGD3 constitute an ATP binding cassette transporter complex residing in the plastid inner envelope, TGD4 is a transmembrane lipid transfer protein present in the outer envelope. These observations raise questions regarding how lipids transit across the aqueous intermembrane space. Here, we describe the isolation and characterization of a novel Arabidopsis thaliana gene, TGD5. Disruption of TGD5 results in similar phenotypic effects as previously described in tgd1,2,3,4 mutants, including deficiency of ER-derived thylakoid lipids, accumulation of oligogalactolipids, and triacylglycerol. Genetic analysis indicates that TGD4 is epistatic to TGD5 in ER-to-plastid lipid trafficking, whereas double mutants of a null tgd5 allele with tgd1-1 or tgd2-1 show a synergistic embryo-lethal phenotype. TGD5 encodes a small glycine-rich protein that is localized in the envelope membranes of chloroplasts. Coimmunoprecipitation assays show that TGD5 physically interacts with TGD1, TGD2, TGD3, and TGD4. Collectively, these results suggest that TGD5 facilitates lipid transfer from the outer to the inner plastid envelope by bridging TGD4 with the TGD1,2,3 transporter complex.
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    • "The LPC generation in the pah and pah lpcat mutants may also involve other enzymes, notably PDAT. PDAT1 was crucial in mediating TAG synthesis when the eukaryotic pathway for chloroplast lipid synthesis was disrupted in the tgd1-1 mutant (Fan et al., 2013). The role of PDAT1 has been previously suggested to be associated with LPCAT activity in the AS11/dgat1 mutant (Xu et al., 2012), which is deficient in the TAG biosynthesis enzyme diacylglycerol acyltransferase (Hobbs et al., 1999; Routaboul et al., 1999; Zou et al., 1999). "
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