Opposite diacylglycerol enantiomeric specificities of Arabidopsis DGAT1 and DGAT2 reveal distinct roles in TAG synthesis

Triacylglycerol (TAG) serves as the primary storage lipid in plants, essential for seed germination and early seedling development. Acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes catalyze the last step in TAG synthesis by converting diacylglycerol (DAG) to TAG. Although functionally conserved across species, DGATs exhibit variations in substrate preference, among their other properties, highlighting their influence on fatty acid (FA) composition in TAG. In this study, we investigated the biochemical properties of Arabidopsis DGATs expressed in yeast with a primary emphasis on understanding the specificity and selectivity of these enzymes on different acyl acceptors and donors. One aim of the study was to investigate if the FA composition of TAG is due to DGAT selectivity in addition to being influenced by the distinct DAG pools (spatially separated de novo synthesized and phosphatidylcholine [PC]-derived DAG). Our findings showed that Arabidopsis (Arabidopsis thaliana) DGAT1 preferentially selects PC-derived DAGs. Further, we also report a new method for synthesizing sn-2,3-DAG that we used to study DGAT enantiomeric specificity. The results revealed that DGAT1 is specific toward the sn-1,2-DAG enantiomer whereas DGAT2 only utilizes sn-2,3-DAG, a substrate that is not directly involved in the Kennedy pathway. DGAT2 has so far not shown significant involvement in de novo TAG synthesis and thus our findings indicate a possible function for DGAT2 in Arabidopsis in TAG remodeling.