Membrane lipids comprise diverse molecular species, and their composition differs from membrane to membrane. In addition, membrane lipid composition changes in response to internal and external cues. Furthermore, within a membrane, there may be microdomains with distinct lipid constituents and particular functions. However, it is not understood how these distinct compositions and their dynamics are generated and what their functions are in the cell. The objectives of this project are to use a metabolomic approach to determine cellular membrane lipid composition and to understand the regulation and role of membrane lipid compositional dynamics in plant responses to stresses. A highly sensitive approach based on electrospray ionization tandem mass spectrometry (ESI-MS/MS) will be established. ESI-MS/MS will be employed to profile membrane lipid molecular species and to determine the compositional dynamics in Arabidopsis plants undergoing temperature and drought stresses. To understand how lipid changes are regulated, this project will investigate enzymes involved in generating the membrane lipid compositional dynamics. Arabidopsis lines, abrogated of various isoforms of phospholipase D, the major lipolytic enzyme family, will be instrumental in the analysis. In addition, lipid molecular species of the defense mutant ssi2 that is defective in stearoyl-ACP desaturase and its suppressor lines will be profiled to determine the relationship between lipid composition and alterations in defense responses. The capability to combine full lipid profiling with cellular analysis of the machinery that generates compositional changes should yield new information on how cellular machinery and metabolites interact in a dynamic manner in the cellular response to changing environments. Membrane lipids are vital biological constituents, providing structural backbones for biological membranes and crucial resources for producing second messengers in regulating cellular and organismal functions. Membrane lipids comprise diverse molecular species, and the composition differs from membrane to membrane. The lipid composition changes in response to internal and external cues. However, it is not understood how these distinct compositions and their dynamics are generated and what their functions are in the cell. This project will establish a highly effective approach based on electrospray ionization tandem mass spectrometry and use it to determine cellular membrane lipid composition and the role of membrane lipid compositional changes in plant responses to stresses. Extensive profiling of membrane lipids and their metabolites will yield unprecedented information on how cellular machinery and metabolites interact in a dynamic manner in the cellular response to changing environments.
