Biosynthesis Of Seed

Genetic engineering has created numerous possibilities for enhancing seed oil content. Prior to entering a discussion of various genetic engineering approaches for enhancing seed oil content, we provide a general overview of the biosynthesis of seed oil based on information from the following detailed reviews on the topic: Stymne and Stobart (1987), Ohlrogge and Browse (1995), Harwood (2005), Weselake (2005), Lung and Weselake (2006), and Cahoon et al. (2007).

Seed oil is predominantly composed of triacylglycerol (TAG), which consists of a glycerol backbone with three esterified fatty acyl groups. A generalized scheme for fatty acid (FA) and TAG biosynthesis in developing seeds of oil crops is shown in Figure 1.1. Enzymes identified as having a key role in enhancing carbon flow into seed oil are indicated with an asterisk. De novo FA biosynthesis occurs in the subcellular organelle known as the plastid through the catalytic action of acetyl-coenzyme A carboxylase (ACCase) and the FA synthase complex. The ACCase-catalyzed reaction provides the malonyl-CoA (coenzyme A) for addition of two-carbon units to the growing FA chain, which is covalently linked to acyl carrier protein (ACP) in the FA synthase complex. A soluble acyl-ACP desaturase catalyzes the formation of monounsaturated FA such as oleate. Acyl-ACP hydrolase (or thioesterase) catalyzes the release of FAs, which in turn move to the outer plastidial membrane, where acyl-CoA synthetase catalyzes their conversion to acyl-CoAs. Molecular species of acyl-CoA derived from plastidial FA can be further elongated and desaturated in the endoplasmic reticulum (ER).

FA synthesis

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