Phospholipid:Diacylglycerol Acyltransferase Is a Multifunctional Enzyme Involved in Membrane Lipid Turnover and Degradation While Synthesizing Triacylglycerol in the Unicellular Green Microalga Chlamydomonas reinhardtii

摘要

Many unicellular microalgae produce large amounts (∼20 to 50% of cell dry weight) of triacylglycerols () under stress (e.g., nutrient starvation and high light), but the synthesis and physiological role of are poorly understood. We present detailed genetic, biochemical, functional, and physiological analyses of phospholipid:diacylglycerol acyltransferase () in the green microalga Chlamydomonas reinhardtii, which catalyzes synthesis via two pathways: transacylation of diacylglycerol () with acyl groups from phospholipids and galactolipids and : transacylation. We demonstrate that also possesses acyl hydrolase activities using , phospholipids, galactolipids, and cholesteryl esters as substrates. Artificial microRNA silencing of PDAT in C. reinhardtii alters the membrane lipid composition, reducing the maximum specific growth rate. The data suggest that -mediated membrane lipid turnover and synthesis is essential for vigorous growth under favorable culture conditions and for membrane lipid degradation with concomitant production of for survival under stress. The strong lipase activity of with broad substrate specificity suggests that this enzyme could be a potential biocatalyst for industrial lipid hydrolysis and conversion, particularly for biofuel production.