Roles of polyunsaturated fatty acids, from mediators to membranes

Polyunsaturated fatty acids (PUFAs), such as arachidonic acid and docosahexaenoic acid, are recognized as important biomolecules, but understanding their precise roles and modes of action remains challenging. PUFAs are precursors for a plethora of signaling lipids, for which knowledge about synthetic pathways and receptors has accumulated. However, due to their extreme diversity and the ambiguity concerning the identity of their cognate receptors, the roles of PUFA-derived signaling lipids require more investigation. In addition, PUFA functions cannot be explained just as lipid mediator precursors, since they are also critical for the regulation of membrane biophysical properties. The presence of PUFAs in membrane lipids also affects the functions of transmembrane proteins and peripheral membrane proteins. Although the roles of PUFAs as membrane lipid building blocks were difficult to analyze, the discovery of lysophospholipid acyltransferases, which are critical for their incorporation, advanced our understanding. Recent studies unveiled how lysophospholipid acyltransferases affect PUFA levels in membrane lipids, and their genetic manipulation became an excellent strategy to study the roles of PUFA-containing lipids. In this review, we will provide an overview of metabolic pathways regulating PUFAs as lipid mediator precursors and membrane components, and update recent progress about their functions. Some issues to be solved for future research will also be discussed.

Characterization and expression analysis of GPAT gene family in maize

Glycerol-3-phosphate acyltransferase (GPAT) catalyzes the initial step of glycerolipids biosynthesis and contributes to oil production, membrane stabilization, and stress responses in plants. In major field crops, little information on the GPAT gene family and their potential stress-related functions were available. In this study, 15 GPAT gene family members were identified from the maize genome and designated as ZmGPAT1–ZmGPAT14 and ZMS1. The ZmGPAT proteins contained 371–557 amino acids and had a molecular weight between 42.7 and 61.2 kDa. Phylogenetic analysis revealed that ZmGPATs fell into four clusters. All 15 ZmGPAT proteins possessed conserved PlsC/LPLAT (phosphate acyltransferases/lysophospholipid acyltransferases) domains and featured multiple acyltransferase motifs. The expression profiles of ZmGPAT genes were different in various tissues of maize and the elevated expression of several ZmGPAT genes occurred at early seed developmental stages. In response to environmental stresses, differential expression of ZmGPATs had been observed, highlighted by the significant induction of transcripts accumulation of some ZmGPATs under cold treatment. This study will help to better understand the potential roles of GPAT in oil production and development and abiotic stress responses in field crops.

Regulation of the yeast triacylglycerol lipases Tgl4p and Tgl5p by the presence/absence of nonpolar lipids

Tgl3p, Tgl4p, and Tgl5p are the major triacylglycerol lipases of the yeast Saccharomyces cerevisiae. Recently we demonstrated that properties of Tgl3p are regulated by the formation of nonpolar lipids. The present study extends these investigations to the two other yeast triacylglycerol lipases, Tgl4p and Tgl5p. We show that Tgl4p and Tgl5p, which are localized to lipid droplets in wild type, are partially retained in the endoplasmic reticulum in cells lacking triacylglycerols and localize exclusively to the endoplasmic reticulum in a mutant devoid of lipid droplets. In cells lacking steryl esters, the subcellular distribution of Tgl4p and Tgl5p is unaffected, but Tgl5p becomes unstable, whereas the stability of Tgl4p increases. In cells lacking nonpolar lipids, Tgl4p and Tgl5p lose their lipolytic activity but retain their side activity as lysophospholipid acyltransferases. To investigate the regulatory network of yeast triacylglycerol lipases in more detail, we also examined properties of Tgl3p, Tgl4p, and Tgl5p, respectively, in the absence of the other lipases. Surprisingly, lack of two lipases did not affect expression, localization, and stability of the remaining Tgl protein. These results suggest that Tgl3p, Tgl4p, and Tgl5p, although they exhibit similar functions, act as independent entities.