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Arabidopsis GPAT9 contributes to synthesis of intracellular glycerolipids but not surface lipids.

ABSTRACT: GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE (GPAT) genes encode enzymes involved in glycerolipid biosynthesis in plants. Ten GPAT homologues have been identified in Arabidopsis. GPATs 4-8 have been shown to be involved in the production of extracellular lipid barrier polyesters. Recently, GPAT9 was reported to be essential for triacylglycerol (TAG) biosynthesis in developing Arabidopsis seeds. The enzymatic properties and possible functions of GPAT9 in surface lipid, polar lipid and TAG biosynthesis in non-seed organs, however, have not been investigated. Here we show that Arabidopsis GPAT9 exhibits sn-1 acyltransferase activity with high specificity for acyl-coenzyme A, thus providing further evidence that this GPAT is involved in storage lipid biosynthesis. We also confirm a role for GPAT9 in seed oil biosynthesis and further demonstrate that GPAT9 contributes to the biosynthesis of both polar lipids and TAG in developing leaves, as well as lipid droplet production in developing pollen grains. Conversely, alteration of constitutive GPAT9 expression had no obvious effects on surface lipid biosynthesis. Taken together, these studies expand our understanding of GPAT9 function to include modulation of several different intracellular glycerolipid pools in plant cells.

SUBMITTER: Singer SD

PROVIDER: S-EPMC4973736 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Arabidopsis GPAT9 contributes to synthesis of intracellular glycerolipids but not surface lipids.

Singer Stacy D SD Chen Guanqun G Mietkiewska Elzbieta E Tomasi Pernell P Jayawardhane Kethmi K Dyer John M JM Weselake Randall J RJ

Journal of experimental botany 20160620 15

GLYCEROL-3-PHOSPHATE ACYLTRANSFERASE (GPAT) genes encode enzymes involved in glycerolipid biosynthesis in plants. Ten GPAT homologues have been identified in Arabidopsis. GPATs 4-8 have been shown to be involved in the production of extracellular lipid barrier polyesters. Recently, GPAT9 was reported to be essential for triacylglycerol (TAG) biosynthesis in developing Arabidopsis seeds. The enzymatic properties and possible functions of GPAT9 in surface lipid, polar lipid and TAG biosynthesis in ...[more]

PMID: 27325892

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Project description:Plants and microalgae have the ability to harness sunlight into energy dense molecules such as triacylglycerols (TAGs). TAGs hold great importance for human and animal nutrition, and are also a source for renewable energy. Acyl-CoA-dependent TAG synthesis by diacylglycerol acyltransferases (DGATs) in oilseeds has been well characterized, but how the ectopic introduction of TAG synthesis in vegetative tissues of plants affects metabolism is largely unknown. Here we report the identification and characterization of several Chlamydomonas reinhardtii Diacylglycerol Acyltransferase Type Two (DGTT) enzymes and their use in engineering TAG biosynthesis in plant vegetative tissues. Focusing on DGTT2 we demonstrate that it can accept a broad range of substrates. Production of DGTT2 in Arabidopsis results in distinct seedling phenotypes and accumulation of TAG with very long chain fatty acids (VLCFA), in both seedlings (23.4-fold increase) and in the leaves of soil-grown plants (13.3-fold increase). Levels of surface lipids, such as waxes and cutins, are decreased in DGTT2-producing lines, consistent with a decreased carbon/acyl flux to the surface lipid pathway. Global transcript analysis showed that very few genes had altered expression. Little to no change in the transcripts of wax/cutin pathway genes was observed in response to altered carbon partitioning into TAGs in the leaves suggesting that the supply of acyl groups for surface lipid biosynthesis is not transcriptionally adjusted in the transgenic lines. As an indication that the DGTT2-producing plants are richer in feed value, the generalist herbivore Spodoptera exigua reared on the transgenic plants gained more weight. Apparently, the substrate specificity of DGTT2 from Chlamydomonas when produced in the Arabidopsis cells leads to diversion of carbon from surface compounds in TAGs and enhances the nutritional value of leaves. 4 biological replicates DGTT2 transgenic plants are compared to 4 biological replicates of wild type

Project description:The intracellular unbound drug concentration (Cu,cell) drives pharmacological and toxicological responses for targets inside cells. We have previously shown that Cu,cell is not always equal to extracellular unbound drug concentrations (e.g. plasma concentrations). However, the underlying mechanisms that drive cellular drug binding are poorly understood. The aim of this study was to evaluate drug binding to individual cellular components, such as neutral lipids (NL) and phospholipids (PL). The fibroblastic 3T3-L1 cell line was used as a cellular model. The cells were either used as wild-type (WT cells) or were treated with a differentiation cocktail that induced an adipocyte-like phenotype with large NL droplets (NL+PL+ cells), or treated with propranolol to induce accumulation of PL (PL+ cells). The three cell types were analysed for morphology, global protein expression, lipid content, cellular volume and lysosomal appearance. The cells were exposed to 23 drugs with diverse physicochemical properties, e.g., with regard to lipophilicity, charge, molecular weight and polar surface area. The cellular binding (fu,cell) and the total accumulation ratio (Kp) were measured and used to obtain the intracellular bioavailability (Fic)—defined as the unbound fraction of the drug concentration added to the cells that is available for intracellular target interaction. The NL+PL+ cells had an adipocyte-like morphology, whereas the PL+ were not visually distinguishable from WT cells. Analysis of the global proteome combined with pathway analysis supported the morphological appearances and confirmed the adipocyte-like phenotype of NL+PL+ cells and the normal morphology of PL+ cells. Fic was significantly altered in both treated cell types as compared to WT. A strong negative correlation between fu,cell and PL content in the cell homogenates was observed, whereas the increased NL content in the NL+PL+ cells did not increase binding further. The importance of PLs for drug binding was confirmed by affinities to beads coated with purified PLs. The NL+PL+ cells lacked acidic subcellular compartments (i.e., endo-lysosomal space), which further influenced the subcellular distribution of cationic drugs. In conclusion, our results suggest that PL content, but not NL content, is a major determinant of drug binding in cells, and that PL beads may constitute a simple alternative to more cumbersome cell distribution studies.

Dataset Information

Arabidopsis GPAT9 contributes to synthesis of intracellular glycerolipids but not surface lipids.

Publications

Arabidopsis GPAT9 contributes to synthesis of intracellular glycerolipids but not surface lipids.

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