Involvement of phosphatidate phosphatase in the biosynthesis of triacylglycerols in Chlamydomonas reinhardtii

Lipid biosynthesis is essential for eukaryotic cells, but the mechanisms of the process in microalgae remain poorly understood. Phosphatidic acid phosphohydrolase or 3-sn-phosphatidate phosphohydrolase(PAP) catalyzes the dephosphorylation of phosphatidic acid to form diacylglycerols and inorganic orthophosphates. This reaction is integral in the synthesis of triacylglycerols. In this study, the mRNA level of the PAP isoform CrPAP2 in a species of Chlamydomonas was found to increase in nitrogen-free conditions. Silencing of the CrPAP2 gene using RNA interference resulted in the decline of lipid content by 2.4%–17.4%. By contrast, over-expression of the CrPAP2 gene resulted in an increase in lipid content by 7.5%–21.8%. These observations indicate that regulation of the CrPAP2 gene can control the lipid content of the algal cells. In vitro CrPAP2 enzyme activity assay indicated that the cloned CrPAP2 gene exhibited biological activities.

Engineering industrial fatty acids in oilseeds

More than 300 types of modified fatty acids （mFA） are produced in triacylglycerols （TAG） by various plant species, with many of these unusual structures rendering unique physical and chemical properties that are desirable for a variety of bio-based industrial uses. Attempts to produce these mFA in crop species have thus far failed to reach the desired levels of production and highlighted the need to better understand how fatty acids are synthesized and accumulated in seed oils. In this review we discuss how some of the progress made in recent years, such as the improved TAG synthesis model to include acyl editing and new enzymes such as PDCT, may be utilized to achieve the goal of effectively modifying plant oils for industrial uses. Co-expressing several key enzymes may circumvent the bottlenecks for the accumulation of mFA in TAG through efficient removal of mFA from phosphatidylchofine. Other approaches include the prevention of feedback inhibition of fatty acid synthesis and improving primary enzyme activity in host transgenic plants. In addition, genomic approaches are providing unprecedented power to discover more factors that may facilitate engineering mFA in oilseeds. Based on the results of the last 20 years, creating a high mFA accumulating plant will not be done by simply inserting one or two genes; it is necessary to stack genes encoding enzymes with favorable kinetic activity or specificity along with additional complementary transgenes in optimized plant backgrounds to produce industrial fatty acids at desirable levels. Finally, we discuss the potential of Camelina as an industrial oilseed platform.