1. Weill Institute for Cell and Molecular Biology and Section of Plant Biology, School of Integrative Plant Science; Cornell University, Ithaca, New York 14853, USA;, ,
2. Reproduction et Développement des Plantes, Université de Lyon, ENS de Lyon, UCB Lyon 1, INRA, CNRS, 69364 Lyon CEDEX 07, France;, ,
3. Current affiliation: Department for Biosystems Science and Engineering, ETH Zurich, 4058 Basel, Switzerland;
4. Theoretical Biology Laboratory, RIKEN, Wako, Saitama 351-0198, Japan;
5. Department of Mathematics, Stockholm University, 106 91 Stockholm, Sweden;