1. Section of Plant Physiology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, NL-1098XH, Amsterdam, The Netherlands
2. Department of Plant Molecular Biology, University of Lausanne-Sorge, Lausanne 1015, Switzerland
3. Present address: Department of Plant and Microbial Biology, University of Zürich, Zürich 8008, Switzerland.
4. Section of Plant Cell Biology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, NL-1098XH, Amsterdam, The Netherlands
5. Section of Molecular Cytology, Swammerdam Institute for Life Sciences (SILS), University of Amsterdam, NL-1098XH, Amsterdam, The Netherlands
6. Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA