1. Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907
2. Center for Plant Biology, Purdue University, West Lafayette, IN 47907
3. Plant Ecology and Evolution, Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Uppsala SE-752 36, Sweden
4. Department of Biochemistry, Purdue University, West Lafayette, IN 47907
5. Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO 80523