Roles of lipids as signaling molecules and mitigators during stress response in plants.

Lipids are the major constituents of biological membranes that can sense extracellular conditions. Lipid-mediated signaling occurs in response to various environmental stresses, such as temperature change, salinity, drought and pathogen attack. Lysophospholipid, fatty acid, phosphatidic acid, diacylglycerol, inositol phosphate, oxylipins, sphingolipid, and N-acylethanolamine have all been proposed to function as signaling lipids. Studies on these stress-inducible lipid species have demonstrated that each lipid class has specific biological relevance, biosynthetic mechanisms and signaling cascades, which activate defense reactions at the transcriptional level. In addition to their roles in signaling, lipids also function as stress mitigators to reduce the intensity of stressors. To mitigate particular stresses, enhanced syntheses of unique lipids that accumulate in trace quantities under normal growth conditions are often observed under stressed conditions. The accumulation of oligogalactolipids and glucuronosyldiacylglycerol has recently been found to mitigate freezing and nutrition-depletion stresses, respectively, during lipid remodeling. In addition, wax, cutin and suberin, which are not constituents of the lipid bilayer, but are components derived from lipids, contribute to the reduction of drought stress and tissue injury. These features indicate that lipid-mediated defenses against environmental stress contributes to plant survival.