1. Department of Biology, McGill University, Montréal, Québec, H3A 1B1, Canada
2. Institut National de la Recherche Scientifique-Institut Armand-Frappier, Laval, Québec, H7V 1B7, Canada
3. Department of Plant and Microbial Biology, University of California, Berkeley, California 94720
4. Facility for Electron Microscopy Research, McGill University, Montréal, Québec, H3A 0C7, Canada
5. Department of Anatomy & Cell Biology, McGill University, Montréal, Québec, H3A 0C7, Canada