9513582 Dewey Biological membranes are complex assemblies of protein and lipid, held together primarily through noncovalent interactions. Of the numerous lipid species found within eukaryotic membranes, phosphatidylcholine (PC) predominates. In higher plants, PC is important not only because of its role as the primary phospholipid constituent of most cellular membranes, but also because it serves as a source of polyunsaturated fatty acids for both membrane lipids and seed storage oils. Although numerous studies have been conducted describing the biochemical pathways responsible for PC production in plants, relatively little is understood about the genes that encode the enzymes involved, or the processes by which cells are able to monitor and maintain appropriate PC levels. The primary objective of this proposal involves the utilization of the soybean Ckase- and CCTase- homologous cDNAs to facilitate a detailed characterization of these genes and their protein products, and better understand their role in the biosynthesis and regulation of PC. The other major objective of this study involves examining the possibility that SEC14p-like proteins in higher plants function as molecular sensors in monitoring and regulating phospholipid content of cellular membranes as has been reported in yeast. The detailed study of genes encoding enzymes of the CDP-choline pathway outlined in this proposal will generate valuable insights into the molecular basis of PC biosynthesis and regulation in higher plants that have not been previously attainable. Furthermore, by characterizing and establishing the function of SEC14p-like proteins in soybean, it may then be possible to begin to answer some of the fundamental questions regarding the mechanisms by which plant cells are able to monitor and regulate the phospholipid content of specific biological membranes.
