Regulation of plant phospholipid biosynthesis

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Phospholipids are essential for the construction of eukaryotic cell membranes, which play a fundamental role in compartmentalising the biochemistry of life. The quantity and composition of phospholipids are tightly regulated during growth and development, and in response to environmental change, so that membranes always maintain their structure and function. Research in mammals and yeast (Saccharomyces cerevisiae) has uncovered elegant metabolite signaling mechanisms, both transcriptional and post-translational, that allow the cell to sense changes in key lipid intermediates and adjust phospholipid synthesis (and turnover) accordingly. Analogous mechanisms are also likely to exist in plants but surprisingly they have not been elucidated. Because phospholipids are essential, genetic analysis of their regulation through loss-of-function is problematic. However, we have recently isolated an Arabidopsis thaliana double mutant in two phosphatidate phosphatases (pah1 pah2) that produces approximately twice as much phospholipid in its leaves as wild type plants. To our knowledge this is the first plant mutant to over-produce phospholipids and the gain-of-function phenotype provides a unique tool. The objective of this grant proposal is to use the pah1 pah2 mutant (and corresponding genes) to discover how phospholipid biosynthesis is regulated in Arabidopsis and to investigate how it is coordinated with cell cycle progression, which requires membrane biogenesis. This discovery will be of fundamental scientific interest, particularly as there is already evidence to show that many key elements of the regulatory mechanism(s) in plants must differ from those described in mammals or yeast.