Aspects of the invention provide methods for differential regulation of fatty acid unsaturation in seed oil and membrane lipids of plants based on modulation of a previously unknown biosynthetic pathway involving a novel phosphatidylcholine: diacylglycerol cholinephosphotransferase (PDCT) that regulates phosphatidylcholine biosynthesis in developing oil seed plants. Specific aspects relate to inventive PDCT polypeptides including, for example, variants, deletions, muteins, fusion proteins, and orthologs thereof (collectively PDCT proteins), to nucleic acids encoding same, to plants comprising such PDCT sequences or proteins or devoid or depleted of such PDCT proteins or sequences, and to methods for generating plants having altered or no PDCT expression and/or activity, including but not limited to methods comprising mutagenesis, recombinant DNA, transgenics, etc.