Catalyzes the terminal and only committed step in triacylglycerol synthesis by using diacylglycerol and fatty acyl CoA as substrates. Required for storage lipid synthesis. Upon expression in E.coli functions weakly as a triacylglycerol synthase, making triacylglycerol (TG) from diolein and long-chain fatty acyl-CoA. Has no wax synthase activity to produce wax esters. a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA (9Z)-octadecenoyl-CoA + di-(9Z)-octadecenoylglycerol = 1,2,3-tri-(9Z-octadecenoyl)-glycerol + CoA Glycerolipid metabolism; triacylglycerol biosynthesis. A possible member of the dormancy regulon. Induced in response to reduced oxygen tension (hypoxia) and low levels of nitric oxide (NO). It is hoped that this regulon will give insight into the latent, or dormant phase of infection. Belongs to the long-chain O-acyltransferase family.