1. Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology, Ghent University, B-9000 Gent, Belgium
2. Molecular Genetics Department, John Innes Centre, Norwich NR4 7UH, United Kingdom
3. Bayer CropScience NV, B-9000 Gent, Belgium
4. Department of Plant Biology, University of Illinois, Urbana, Illinois 61801