SPO14 separation-of function mutations define unique roles for phospholipase D in secretion and cellular differentiation in Saccharomyces cerevisiae

in Saccharomyces cervisiae, phospholipase D (PLD), encoded by the SPO14 gen e, catalyzes the hydrolysis of phosphatidylcholine, producing choline and p hosphatidic acid, SPO14 is essential for cellular differentiation during me iosis and is required for Golgi function when the normal secretory apparatu s is perturbed (Sec14-independent secretion). We isolated specific alleles of SPO14 that support Sec14-independent secretion but not sporulation. Iden tification of these separation-of-function alleles indicates that the role of PLD in these two physiological processes is distinct. Analyses of the mu tants reveal that the corresponding proteins are stable, phosphorylated, ca talytically active in vitro, and can localize properly within the cell dini ng meiosis. Surprisingly, the separation-of-function mutations map to the c onsened catalytic region of the PLD protein. Choline and phosphatidic acid molecular species profiles during Sec14-independent secretion and meiosis r eveal that while strains harboring one of these alleles, spo14S-11, hydroly ze phosphatidylcholine in Sec14-independent secretion, they fail to do so d uring sporulation or normal vegetative growth. These results demonstrate th at Spo14 PLD catalytic activity and cellular function can be differentially regulated at the level of phosphatidylcholine hydrolysis.