Catalytic subunit of the alternative triglyceride biosynthesis pathway, which mediates formation of triacylglycerol from diacylglycerol and membrane phospholipids. Synthesizes triacylglycerol at the expense of membrane phospholipids, such as phosphatidylcholine (PC) and its ether-linked form (ePC), thereby altering the composition of membranes. The alternative triglyceride biosynthesis pathway is probably required to provide the energy required for rapid growth when fuel sources are limiting. It maintains mitochondrial function during periods of extracellular lipid starvation. Can also use acyl-CoA as donor: acts as a acyl-CoA:monoacylglycerol acyltransferase (MGAT), but also shows acyl-CoA:diacylglycerol acyltransferase (DGAT) activity