Phosphatidic acid phosphatase (PAP) catalyses the committed step of triacylglycerol (TAG) biosynthesis and thus regulates the amounts of TAG produced by the cell. TAG is the target of biotechnological processes developed for the production of food lipids or biofuels. These processes are using oleaginous microorganisms like the yeast Yarrowia lipolytica as the TAG producers. Thus manipulating key enzymatic activities like PAP in Y. lipolytica could drive lipid biosynthesis towards TAG production and increase TAG yields. In this study, PAP activity in Y. lipolytica was characterized in detail and its role in lipid biosynthesis was addressed. PAP activity increased 2.5-fold with the addition of Mg (1 mm) in the assay mixture, which means that most of the PAP activity was due to Mg -dependent PAP enzymes (e.g. Pah1, App1). In contrast, N-ethylmaleimide (NEM) potently inhibited PAP activity, indicating the presence of NEM-sensitive PAP enzymes (e.g. App1, Lpp1). Localization studies revealed that the majority of PAP activity resides in the membrane fraction, while the cytosolic fraction harbours only a small amount of activity. PAP activity was regulated in a growth-dependent manner, being induced at the early exponential phase and declining thereafter. PAP activity did not correlate with TAG synthesis, which increased as cells progressed from the exponential phase to the early stationary phase. In stationary phase, TAG was mobilized with the concomitant synthesis of sterols and sterol esters. These results provide the first insights into the role of PAP in lipid biosynthesis by Y. lipolytica. Copyright © 2016 John Wiley & Sons, Ltd.

The PAH1-encoded phosphatidate phosphatase (PAP) catalyzes the Mg 2+ -dependent dephosphorylation of phosphatidate to produce diacylglycerol, which can be acylated to form triacylglycerol (TAG). In the model oleaginous yeast Yarrowia lipolytica, TAG is the major lipid produced, and its biosynthesis requires a continuous supply of diacylglycerol, which can be provided by the PAP reaction. However, the regulation of Pah1 has not been studied in detail in Y. lipolytica, and thus its contribution to the biosynthesis of TAG in this yeast is not well understood. In this work, we examined

Phosphatidate (PA) phosphatase dephosphorylates the membrane phospholipid PA to diacylglycerol (DAG) that can be used for the synthesis of the storage lipid triacylglycerol (TAG). In Yarrowia lipolytica, TAG biosynthesis is induced during the lipogenic phase, which results in the accumulation of this lipid in cells. The accumulation of TAG during lipogenesis requires the supply of DAG, but the source of this DAG is not known in Y. lipolytica. In this study, the regulation of PA phosphatase during lipogenesis and its contribution to TAG biosynthesis was examined in Y. lipolytica. Lipogenesis was triggered by growing cells in high-glucose media, whereas control cultures were grown in low-glucose media. PA phosphatase activity increased in a time-dependent manner as high-glucose cells progressed in the lipogenic phase. In contrast, the activity decreased in low-glucose cells that did not accumulate lipids. An analysis of the subcellular localization of the PA phosphatase activity showed that the membrane-associated activity increased during lipogenesis. The significance of this increase can be explained by the fact that only the membrane-associated PA phosphatase activity is responsible for the production of DAG. Taken together, these results indicate that PA phosphatase is involved in TAG biosynthesis during lipogenesis in Y. lipolytica.

Polyunsaturated fatty acids (PUFAs) have been used as dietary supplements for quite some time with various health claims. Major dietary PUFAs are classified as omega-3 and omega-6 based on their structure, and these fatty acids are considered essential nutrients. The two classes of PUFAs, although structurally similar, present different biological activities that can be beneficial or detrimental to humans. Some of these biological activities have been known for a long time, while others are emerging from the plethora of dietary studies done on PUFAs. Yet many of the health claims for PUFAs are still debated, with the findings being conflicting. This review summarizes our current knowledge on the biological activities of PUFAs and discusses the dietary sources available. In light of new dietary recommendations, PUFA consumption is on the rise, so new dietary sources for these fatty acids are needed.

Phosphatidic acid phosphatase (PAP) catalyzes the conversion of phosphatidic acid to diacylglycerol, which is considered the committed step in triacylglycerol (TAG) biosynthesis. TAG biosynthesis in oleaginous microorganisms like Yarrowia lipolytica is typically triggered by high glucose amounts and results in cells accumulating lipids made mostly of TAGs. The objective of this work was to study the regulation of PAP during lipid accumulation induced by high glucose amounts. We hypothesized that the induction of TAG biosynthesis under these conditions should be mediated by PAP. In this work, we grew Y. lipolytica in a high glucose media (HGM) that favors lipid accumulation and in a low glucose media (LGM) where lipid accumulation is minimal. We measured PAP activity and lipid amounts throughout the cultivation period. Our results showed that, over time, the TAG amounts increased eight‐fold in the HGM cultures, while there was no increase in the LGM cultures. PAP activity was induced during TAG accumulation in HGM, which resulted in a two‐fold increase in activity. In contrast, PAP activity was down‐regulated in the LGM cultures, and that decrease coincided with the complete consumption of glucose in the medium. These results indicate that PAP plays a role in the regulation of lipid accumulation in Y. lipolytica.Support or Funding InformationThis project was supported by the Evans‐Allen Grant no.1005735 and Capacity BuildingGrants Program Grant no.1007503 from the USDA National Institute of Food and Agriculture.