Major contributor to triacylglycerol (TAG) synthesis and oil accumulation in developing seeds. Catalyzes the acylation of the sn-3 hydroxy group of sn-1,2-diacylglycerol using acyl-CoA (PubMed:23322364, PubMed:27345221). Has a marked preference for oleoyl-CoA (18:1) and sn-1,2-dioleoylglycerol over vernoloyl-CoA and sn-1,2-divernoloylglycerol (PubMed:23322364). Can use oleoyl-CoA, linoleoyl-CoA and linolenoyl-CoA as substrates (PubMed:27345221). a 1,2-diacyl-sn-glycerol + an acyl-CoA = a triacyl-sn-glycerol + CoA Glycerolipid metabolism; triacylglycerol biosynthesis. Highly expressed in flowers and pods. Expressed at low levels in roots, stems and leaves. During seed development, expressed from 15 to 55 days after flowering (DAF), with a peak at 35 DAF. Induced by heat shock, insect biting and abscisic acid (ABA). Down-regulated by cold stress and treatment with jasmonate. Belongs to the membrane-bound acyltransferase family. Sterol o-acyltransferase subfamily.