Acyl-CoA-dependent and acyl-CoA-independent pathways for TAG biosynthesis in plants

Schematic representation of acyl-CoA-dependent and acyl-CoA-independent pathways for TAG biosynthesis in plants. The Kennedy pathway involving acyl-CoA-dependent acyltransferases (GPAT, LPAT, and DGAT) includes an intervening PA intermediate that is hydrolyzed by PAP to form DAG. Two DGAT classes operate in plant TAG synthesis, and the relative contribution may be dependent upon the plant species and the specific types of FAs stored in TAG. Labeling studies of soybeans indicate that much of the newly synthesized FA supplied from the plastids rapidly enters an acyl-CoA pool that is incorporated into PC by acyl-editing reactions presumably via LPCAT. Acyl groups are desaturated or modified (e.g. hydroxylation) while esterified to PC and then released back to the acyl-CoA pool, where they may co-mingle with newly synthesized acyl-CoAs and are incorporated into glycerolipids by Kennedy pathway enzymes on a slower time course. The rapidly labeled PC pool is used to generate DAG (and vice versa) via PDCT (or CPT). TAG also can be synthesized from DAG and PC by PDAT, yielding lyso-PC, which can be reacylated to form PC. Net synthesis of PC from DAG is accomplished by CPT. PC can be hydrolyzed to PA by phospholipase D (PLD) or to DAG by phospholipase C (PLC; not shown) for TAG synthesis. This diagram does not account for separate pools of intermediates, which are likely. The relative contribution and combination of these alternative pathways to the overall flux to TAG in plants are tissue- and species-specific. Cho, choline; LPA, lysophosphatidic acid; LPC, lyso-PC; PLA, phospholipase A.

Publication

Compartmentation of Triacylglycerol Accumulation in Plants. (2012) Kent D. Chapman, et al. J Biol Chem. 2012 Jan 20;287(4):2288-2294. Figure: F2. All organisms Homo sapiens Drosophila melanogaster

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