Abstract: Triacylglycerols (TAGs) represent the most efficient form of energy storage in eukaryotic cells. TAGs in plants are major sources of essential polyunsaturated fatty acids in the human diet and in renewable feedstock for the chemical industry. Diacylglycerol transacylase, which is encoded by the TAG1 gene, regulates TAG biosynthesis. The Arabidopsis thaliana mutant as11 has a mutation in TAG1. In this review, we summarize the recent progress in the biological characterization of as11 and the lipid biosynthesis regulation by TAG1.