A lipid viewpoint on the plant endoplasmic reticulum stress response

This review discusses the plant unfolded protein response from the perspective of membrane phospholipids in comparison with the respective systems in other model organisms. Organisms, including humans, seem to be constantly exposed to various changes, which often have undesirable effects, referred to as stress. To keep up with these changes, eukaryotic cells may have evolved a number of relevant cellular processes, such as the endoplasmic reticulum (ER) stress response. Owing to presumably intimate links between human diseases and the ER function, the ER stress response has been extensively investigated in various organisms for a few decades. Based on these studies, we now have a picture of the molecular mechanisms of the ER stress response, one of which, the unfolded protein response (UPR), is highly conserved among yeasts, mammals, higher plants, and green algae. In this review, we attempt to highlight the plant UPR from the perspective of lipids, especially membrane phospholipids. Phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) are the most abundant membrane phospholipids in eukaryotic cells. The ratio of PtdCho to PtdEtn and the unsaturation of fatty acyl tails in both phospholipids may be critical factors for the UPR, but the pathways responsible for PtdCho and PtdEtn biosynthesis are distinct in animals and plants. We discuss the plant UPR in comparison with the system in yeasts and animals in the context of membrane phospholipids.