Catalyzes the conversion of phosphatidic acid (PA) to CDP-diacylglycerol (CDP-DAG), an essential intermediate in the synthesis of phosphatidylglycerol, cardiolipin and phosphatidylinositol. Exhibits almost no acyl chain preference for PA, showing no discrimination for the sn-1/sn-2 acyl chain composition of PAs. Plays an important role in regulatinng the growth of lipid droplets which are storage organelles at the center of lipid and energy homeostasis. Positively regulates the differentiation and development of adipocytes 