1. Centre for Plant Molecular Biology (ZMBP) University of Tübingen 72076 Tübingen Germany
2. Department of Biology Colorado State University Fort Collins CO 80523‐1878 USA
3. Department of Biology University of North Carolina Chapel Hill NC 27599 USA
4. Laboratoire Reproduction et Développement des Plantes (RDP) Université de Lyon ENS de Lyon UCB Lyon 1 CNRS INRAE 69264 Lyon France
5. Howard Hughes Medical Institute University of North Carolina Chapel Hill NC 27599 USA