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Review
. 2021 Feb 5;22(4):1621.
doi: 10.3390/ijms22041621.

Molecular Control of Oil Metabolism in the Endosperm of Seeds

Romane Miray  1 , Sami Kazaz  1 , Alexandra To  1 , Sébastien Baud  1
Affiliations
Review

Molecular Control of Oil Metabolism in the Endosperm of Seeds

Romane Miray et al. Int J Mol Sci. .

Abstract

In angiosperm seeds, the endosperm develops to varying degrees and accumulates different types of storage compounds remobilized by the seedling during early post-germinative growth. Whereas the molecular mechanisms controlling the metabolism of starch and seed-storage proteins in the endosperm of cereal grains are relatively well characterized, the regulation of oil metabolism in the endosperm of developing and germinating oilseeds has received particular attention only more recently, thanks to the emergence and continuous improvement of analytical techniques allowing the evaluation, within a spatial context, of gene activity on one side, and lipid metabolism on the other side. These studies represent a fundamental step toward the elucidation of the molecular mechanisms governing oil metabolism in this particular tissue. In particular, they highlight the importance of endosperm-specific transcriptional controls for determining original oil compositions usually observed in this tissue. In the light of this research, the biological functions of oils stored in the endosperm of seeds then appear to be more diverse than simply constituting a source of carbon made available for the germinating seedling.

Keywords: endosperm; fatty acid; metabolism; oil; seed.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Overview of fatty acid metabolism in maturing seeds of Elaeis guineensis and Arabidopsis thaliana. The scheme depicts the different pathways involved in the synthesis and elongation of fatty acids in maturing seeds. Enzymatic steps transcriptionally induced in the endosperm with respect to the embryo are denoted in red and highlighted in white boxes. 1, pyruvate dehydrogenase; 2, acetyl-coenzyme A carboxylase; 3, malonyl-coenzyme A:acyl carrier protein S-malonyltransferase; 4, fatty acid synthase complex comprising 3-ketoacyl-ACP synthase III; 5, fatty acid synthase complex comprising 3-ketoacyl-ACP synthase I; 6, fatty acid synthase complex comprising 3-ketoacyl-ACP synthase II; 7, Δ9 stearoyl-acyl carrier protein desaturase; 8, Δ9 palmitoyl-acyl carrier protein desaturase; 9, FatA fatty acyl-ACP thioesterase; 10, FatB fatty acyl-ACP thioesterase; 11, Specialized FatB fatty acyl-ACP thioesterase releasing medium-chain fatty acids; 12, long-chain acyl-coenzyme A synthetase; 13, fatty acid elongase complex. Abbreviations: ACP, acyl carrier protein; CoA, coenzyme A; LCFA, long-chain fatty acid; VLCFA, very-long-chain fatty acid.
Figure 2
Figure 2
Overview of oil metabolism in maturing seeds of Elaeis guineensis and Ricinus communis. The scheme depicts the different pathways involved in the assembly of storage lipids in maturing seeds. Enzymatic steps transcriptionally induced in the endosperm with respect to the embryo are denoted in red and highlighted in white boxes. Blue dashed arrows denote enzymatic steps transcriptionally repressed in the endosperm. 12, long-chain acyl-coenzyme A synthetase; 14, Δ12 fatty acid desaturase; 15, Δ15 fatty acid desaturase; 16, Δ12 fatty acid hydroxylase; 17, acyl-coenzyme A:sn-glycerol-3-phosphate acyltransferase; 18, acyl-coenzyme A:lysophosphatidic acid acyltransferase; 19, phosphatidic acid phosphohydrolase; 20, acyl-coenzyme A:1,2-diacyl-sn-glycerol acyltransferase; 21, CDP-choline:1,2-sn-diacylglycerol choline phosphotransferase; 22, phosphatidylcholine:1,2-sn-diacylglycerol choline phosphotransferase; 23, phospholipid:1,2-sn-diacylglycerol acyltransferase; 24, phospholipase A2; 25, acyl-coenzyme A: lysophosphatidylcholine acyltransferase. Abbreviations and symbols: *, acyl-CoA; CoA, coenzyme A; DAG, diacylglycerol; ER, endoplasmic reticulum; FA, fatty acid; LPA, lysophosphatidic acid; LPC, lysophosphatidylcholine; PA, phosphatidic acid; PC, phosphatidylcholine; TAG, triacylglycerol; VLCFA, very-long-chain fatty acid.
Figure 3
Figure 3
Fatty acid composition of endosperm and embryo oils in seeds of different species. (A). Argania spinosa. (B). Paeonia ostii. (C). Elaeis guineensis. (D). Arabidopsis thaliana. For each species considered, a pie chart presents the repartition of seed oil between embryo and endosperm tissues. Circular charts present the relative proportions of the main fatty acid species comprising endosperm and embryo oils, respectively. The relative abundance of unusual fatty acids in each compartment is indicated in the center of the circular charts. FA, fatty acid; MCFA, medium-chain fatty acid.
Figure 4
Figure 4
Overview of oil metabolism in germinating seeds. The scheme depicts the different pathways involved in the mobilization of storage lipids in germinating seeds. 12, long-chain acyl-CoA synthetase; 26, triacylglycerol lipase; 27, acyl-CoA oxidase; 28, multifunctional protein 2-trans-enoyl-CoA hydratase; 28′, multifunctional protein 1,3-hydroxyacyl-CoA dehydrogenase; 29, 3-ketoacyl-CoA thiolase; 30, citrate synthase; 31, aconitase; 32, isocitrate lyase; 33, malate synthase; 34, malate dehydrogenase; 35, succinate dehydrogenase; 36, fumarase; 37, phosphoenolpyruvate carboxykinase; 38, glycerol kinase; 39, glycerol-3-phosphate dehydrogenase. Abbreviations: CoA, coenzyme A; DAG, diacylglycerol; FA, fatty acid; MAG, monoacylglycerol; TAG, triacylglycerol.
Figure 5
Figure 5
Oil mobilization in germinating seeds. The schemes illustrate different strategies for the mobilization of storage lipids and the allocation of carbon to the seedling. (A). In the aleurone layer of cereal grains, lipid mobilization supports the synthesis of α-amylases that are secreted into the dead starchy endosperm to mobilize starch, releasing nutrients that are absorbed by the scutellum. (B). In non-cereal monocots in the family Aracaceae, fatty acids released from triacylglycerol by lipases in the endosperm are thought to be transported to the haustorium, where enzymes of ß-oxidation are located. (C). In seeds of oleaginous dicots, triacylglycerol mobilization and gluconeogenesis take place in the endosperm and sugars are transported to the seedling. (D). Although this hypothesis remains to be validated, direct supply of triacylglycerol from the endosperm to the seedling was also proposed. Abbreviations: α-Am, α-amylase; ß-ox., ß-oxidation; FA, fatty acid; SUC, sucrose; TAG, triacylglycerol.
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