Plant seed triacylglycerol (oil) biosynthesis module

A taxon-neutral decomposition of plant seed storage-oil (triacylglycerol, TAG) assembly as a recursively decomposable module. In developing oilseeds, acyl groups (produced by plastidial fatty acid synthesis and activated as acyl-CoA) are assembled onto a glycerol backbone at the endoplasmic reticulum by the glycerol-phosphate (Kennedy) pathway and packaged into cytosolic oil bodies (lipid droplets) stabilized by oleosins. The module separates (1) acylation of glycerol-3-phosphate to lysophosphatidic acid (GPAT), (2) acylation of LPA to phosphatidic acid (LPAAT), (3) dephosphorylation of PA to diacylglycerol (PAP), (4) the final acyl transfer to DAG forming TAG by two alternative routes - acyl-CoA-dependent (DGAT1/DGAT2) and acyl-CoA-independent (PDAT, using phospholipid acyl donors) - and (5) oil-body biogenesis and oleosin stabilization. It is phrased as functions and pathway segments rather than a fixed gene list so it can represent Arabidopsis and crop oilseeds (soybean, rapeseed/canola, oil palm, camelina); concrete UniProt members are Arabidopsis exemplars, not species-restricting claims. Plastidial de novo fatty acid synthesis, acyl-chain desaturation/modification, and TAG catabolism (lipolysis/beta-oxidation) are upstream/downstream and out of scope. As a bioenergy module, total TAG flux (DGAT/PDAT capacity), the acyl-CoA pool, and oil-body number/size (oleosin dosage) are the principal engineering levers for raising seed-oil yield for biodiesel and oleochemical feedstocks.

Identifiers are grounded only where verified against the local GO term cache or UniProt; descriptors without a `term` (e.g. acyl-CoA donor, glycerolipid intermediates) are deliberate rather than oversights. The final TAG step is represented as a variant set because plants use two mechanistically distinct routes - acyl-CoA-dependent DGAT1/DGAT2 and acyl-CoA-independent PDAT1 - that are genetically redundant in Arabidopsis (dgat1 pdat1 double mutants are pollen/seed lethal for oil). Some DAG can also be recruited from the phosphatidylcholine acyl-editing pool rather than solely de novo PAP output; that acyl-editing cycle is acknowledged but not expanded here. Representative UniProt members are concrete Arabidopsis exemplars for orientation, not exhaustive or species-restricting; crop oilseeds use orthologous machinery.