1. , Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique Centre Versailles, F‐78026 Versailles Cedex, France,, Institut Biologie II, Albert‐Ludwigs‐Universität Freiburg, Schänzlestr. 1, D‐79104 Freiburg, Germany, and, Biology Department, University of Waterloo, ON, Canada N2L 3G1