The role of phospholipase D in vesicle fusion

During sporulation in the budding yeast Saccharomyces cerevisiae, the spindle poles serve as sites for the de novo assembly of new intracellular membranes termed prospore membranes. Prospore membranes engulf daughter nuclei produced by the meiotic divisions and ultimately serve as plasma membranes for the newly formed spores. The initial fusion of precursor vesicles to create prospore membranes occurs on the surface of the spindle pole body. Translocation of the phospholipase D Spo14 from its endosomal/cytoplasmic localization in vegetative cells to these precursor vesicles and the catalytic activity of the enzyme are essential for precursor vesicle fusion. Spo14‐generated phosphatidic acid (PA) plays multiple roles in stimulating vesicle fusion. Elevated PA levels are necessary to recruit one of the subunits of a prospore membrane‐specific SNARE complex to the membrane. Independent of SNARE recruitment, PA within the membrane also enhances the ability of this SNARE complex to mediate fusion. However, additional roles for PA are indicated by the observation that SPO14 is still essential for precursor vesicle fusion even in the presence of a modified SNARE that can bypass both of these PA requirements. The additional role(s) of phospholipase D in regulating this fusion event, as well as the mechanism by which Spo14 is translocated to precursor vesicles will be discussed.