Abstract #14

The phospholipase D, Spo14p, and t-SNARE, Sso1p, are required for vesicle fusion in prospore membrane formation. Hideki Nakanishi¹, Masayo Morishita², Cindi L. Schwartz³, Alison Coluccio¹, JoAnne Engebrecht², Aaron M. Neiman¹. 1) Biochemistry and Cell Biology, SUNY Stony Brook, Stony Brook, NY; 2) Section of Molecular and Cellular Biology, UC Davis, Davis, CA; 3) Boulder Laboratory for 3D Electron Microscopy of Cells, University of Colorado, Boulder, CO.
   In sporulation, post-Golgi vesicles are recruited to the spindle pole body (SPB) and fuse together to create the prospore membrane. We found that spo14D and sso1D mutants show a similar defect in prospore membrane formation such that precursor vesicles accumulate on the SPB. Spo14p is a phospholipase D (PLD) producing phosphatidic acid (PA) on the prospore membrane in sporulation. Spo20p, a soluble SNARE protein, is recruited to the prospore membrane through its lipid binding domain. The localization of the lipid binding domain to the prospore membrane is dependent on SPO14, suggesting that Spo14p-generated PA is required for Spo20p recruitment. However, independent localization of Spo20p to the prospore membrane is not sufficient to promote vesicle fusion in absence of SPO14. Thus, PLD has multiple roles in vesicle fusion during prospore membrane formation.
   Sso1p, a syntaxin homologue, has a glutamine residue (Q224) at the center of the SNARE domain. Although the glutamine residue is well conserved in syntaxin family proteins, mutations which change Q224 to any amino acids except P, R, or K did not have effects on Sso1p function in vegetative growth. However, these mutations cause significant sporulation defects, suggesting that the evolutionally conserved glutamine residue has an important role in prospore membrane formation.

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