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: 9.58). 09/2013; DOI: 10.1105/tpc.113.117358
Source: PubMed

ABSTRACT 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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    ABSTRACT: Triacylglycerol (TAG) metabolism is a key aspect of intracellular lipid homeostasis in yeast and mammals, but its role in vegetative tissues of plants remains poorly defined. We previously reported that PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) is crucial for diverting fatty acids (FAs) from membrane lipid synthesis to TAG and thereby protecting against FA-induced cell death in leaves. Here, we show that overexpression of PDAT1 enhances the turnover of FAs in leaf lipids. Using the trigalactosyldiacylglycerol1-1 (tgd1-1) mutant, which displays substantially enhanced PDAT1-mediated TAG synthesis, we demonstrate that disruption of SUGAR-DEPENDENT1 (SDP1) TAG lipase or PEROXISOMAL TRANSPORTER1 (PXA1) severely decreases FA turnover, leading to increases in leaf TAG accumulation, to 9% of dry weight, and in total leaf lipid, by 3-fold. The membrane lipid composition of tgd1-1 sdp1-4 and tgd1-1 pxa1-2 double mutants is altered, and their growth and development are compromised. We also show that two Arabidopsis thaliana lipin homologs provide most of the diacylglycerol for TAG synthesis and that loss of their functions markedly reduces TAG content, but with only minor impact on eukaryotic galactolipid synthesis. Collectively, these results show that Arabidopsis lipins, along with PDAT1 and SDP1, function synergistically in directing FAs toward peroxisomal β-oxidation via TAG intermediates, thereby maintaining membrane lipid homeostasis in leaves.
    The Plant Cell 10/2014; 26(10). DOI:10.1105/tpc.114.130377 · 9.58 Impact Factor
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    ABSTRACT: Phosphatidylcholine (PC) is a key intermediate in the metabolic network of glycerolipid biosynthesis. Lysophosphatidylcholine acyltransferase (LPCAT) and phosphatidic acid phosphatase (PAH) are two key enzymes of PC homeostasis. We report that LPCAT activity was markedly induced in the Arabidopsis pah mutant. A quadruple mutant pahlpcat, with dual defects in PAH and LPCAT, had a level of lysophosphatidylcholine (LPC) much higher than lpcat and a PC content surpassing pah. Comparative molecular profile analysis of monogalactosyldiacylglycerol and digalactosyldiacylglycerol revealed that both pah and pahlpcat had increased proportions of 34:6 from the prokaryotic pathway despite of contrasting levels of LPCAT activity. We show that a decreased representation of C16:0C18:2 diacylglycerol (DAG) moiety in PC was a shared feature of pah and pahlpcat, and that this PC metabolic profile change was correlated with the increased prokaryotic contribution to chloroplast lipid synthesis. We detected increased PC deacylation in pahlpcat that was attributable at least in part to the induced phospholipases (PLAs). An elevated LPC generation was also evident in pah but the PLAs were not induced, raising the possibility that PC deacylation was mediated by the reverse reaction of LPCAT. We discuss possible roles of LPCAT and PAH in PC turnover that impacts lipid pathway coordination for chloroplast lipid synthesis.This article is protected by copyright. All rights reserved.
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    ABSTRACT: Phospholipid:diacylglycerol acyltransferase (PDAT) is an enzyme that catalyzes the transfer of a fatty acyl moiety from the sn-2-position of a phospholipid to the sn-3-position of sn-1, 2-diacylglyerol, thus forming triacylglycerol (TAG) and a lyso-phospholipid. Although the importance of PDAT in TAG biosynthesis has been illustrated in some previous studies, the evolutionary relationship of plant PDATs has not been studied in detail. In this study, we investigated the evolutionary relationship of the PDAT gene family across the green plants using a comparative phylogenetic framework. We found that the PDAT candidate genes are present in all examined green plants, including algae, lowland plants (a moss and a lycophyte), monocots and eudicots. Phylogenetic analysis revealed the evolutionary division of the PDAT gene family into seven major clades. The separation is supported by the conservation and variation in the gene structure, protein properties, motif patterns and/or selection constraints. We further demonstrated that there is a eudicot-wide PDAT gene expansion, which appears to have been mainly caused by the eudicot-shared ancient gene duplication and subsequent species-specific segmental duplications. In addition, selection pressure analyses show that different selection constraints have acted on three core eudicot clades, which might enable paleo-duplicated PDAT paralogs to either become non-functionalized or develop divergent expression pattern during evolution. Overall, our study provides important insights into the evolution of the plant PDAT gene family and explores the evolutionary mechanism underlying the functional diversification among the core eudicot PDAT paralogs. Copyright © 2015, American Society of Plant Biologists.
    Plant physiology 01/2015; DOI:10.1104/pp.114.253658 · 7.39 Impact Factor


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Jul 14, 2014