Plant Phospholipid Diversity: Emerging Functions in Metabolism and Protein–Lipid Interactions

In recent years, plant phospholipid research was greatly advanced by the characterization of numerous mutants affected in phospholipid biosynthesis. Now, we have an almost complete version of the phospholipid metabolic map including genes for each reaction step. In addition to the primary classification of phospholipids according to the structure of the polar head group, the secondary classification based on the hydrophobic acyl tails adds a further level of complexity. This spatiotemporally diverse and dynamic molecular profile of phospholipids determines the physical properties of the membranes, and thus affects the structure and function of each organellar membrane. An increasing number of lipid-binding proteins reported in recent years have rendered protein–lipid interaction analyses an emerging field of ‘interactome research’ in plant biology. Some phospholipid molecular species show oscillation in response to diurnal condition. This may create an oscillatory profile of protein–lipid binding and regulate protein functions by the oscillation of interacting phospholipid. Phospholipids are essential components of biological membranes and signal transduction cascades in plants. In recent years, plant phospholipid research was greatly advanced by the characterization of numerous mutants affected in phospholipid biosynthesis and the discovery of a number of functionally important phospholipid-binding proteins. It is now accepted that most phospholipids to some extent have regulatory functions, including those that serve as constituents of biological membranes. Phospholipids are more than an inert end product of lipid biosynthesis. This review article summarizes recent advances on phospholipid biosynthesis with a particular focus on polar head group synthesis, followed by a short overview on protein–phospholipid interactions as an emerging regulatory mechanism of phospholipid function in arabidopsis (Arabidopsis thaliana). Phospholipids are essential components of biological membranes and signal transduction cascades in plants. In recent years, plant phospholipid research was greatly advanced by the characterization of numerous mutants affected in phospholipid biosynthesis and the discovery of a number of functionally important phospholipid-binding proteins. It is now accepted that most phospholipids to some extent have regulatory functions, including those that serve as constituents of biological membranes. Phospholipids are more than an inert end product of lipid biosynthesis. This review article summarizes recent advances on phospholipid biosynthesis with a particular focus on polar head group synthesis, followed by a short overview on protein–phospholipid interactions as an emerging regulatory mechanism of phospholipid function in arabidopsis (Arabidopsis thaliana). phospholipids contain long-chain acyl group(s) esterified to a hydroxyl group of glycerol backbone. The acyl groups establish the hydrophobic (nonpolar) tails of the phospholipid. It should be noted that the acyl groups show structural variability within the same lipid class. In arabidopsis, typical fatty acids contain 16 or 18 carbon atoms with 0–3 double bonds. The fatty acid composition differs among different glycerolipid classes, and among different organelles, cell types, tissues, or organs. Since the choice and the positional specificity of the acyl groups considerably affect the physical property of a glycerolipid molecule, the fatty acid composition is as important as the polar head group in discussing glycerolipid function. a group of lipid molecules categorized by a common functional group. In phospholipids, they are commonly categorized by the polar, phosphate-containing head group. Therefore, for example, PC and PE are different ‘lipid classes’ that belong to the phospholipids. glycerolipids are lipids that contain a glycerol backbone and at least one acyl group esterified to one of the three hydroxyl groups. Polar glycerolipids harbor a polar head group esterified via phosphoester bonds to the hydroxyl group at the sn-3 position of glycerol. Because two acyl groups are esterified at the other two hydroxyl bonds of glycerol (at sn-1 and sn-2 positions; only one acyl group in case of the lyso-glycerolipid), the polar glycerolipid has both hydrophilic and hydrophobic parts that are important for the formation of the lipid bilayer. Phospholipids are the major classes of membrane glycerolipids in many organisms. However, in photosynthetic membranes, galactolipids (MGDG and DGDG) and sulfolipids (SQDG) are abundant, which have a sugar but not a phosphoalcohol in the polar head group. An example of a nonpolar glycerolipid is triacylglycerol, which is not a membrane lipid but a storage lipid typically found in a lipid droplet.