SP014 separation of function mutants define unique roles for PLD in secretion and cellular differentiation in Saccharomyces cerevisiae

in Saccharomyces cervisiae, phospholipase D (PLD), encoded by the SPO14 gene, catalyzes the hydrolysis of phosphatidylcholine, producing choline and phosphatidic acid, SPO14 is essential for cellular differentiation during meiosis and is required for Golgi function when the normal secretory apparatus is perturbed (Sec14-independent secretion). We isolated specific alleles of SPO14 that support Sec14-independent secretion but not sporulation. Identification of these separation-of-function alleles indicates that the role of PLD in these two physiological processes is distinct. Analyses of the mutants reveal that the corresponding proteins are stable, phosphorylated, catalytically active in vitro, and can localize properly within the cell dining meiosis. Surprisingly, the separation-of-function mutations map to the consened catalytic region of the PLD protein. Choline and phosphatidic acid molecular species profiles during Sec14-independent secretion and meiosis reveal that while strains harboring one of these alleles, spo14S-11, hydrolyze phosphatidylcholine in Sec14-independent secretion, they fail to do so during sporulation or normal vegetative growth. These results demonstrate that Spo14 PLD catalytic activity and cellular function can be differentially regulated at the level of phosphatidylcholine hydrolysis.