1. Division of Biological Sciences, University of California San Diego, La Jolla, CA 92093, USA.
2. Department of Plant Pathology and Microbiology, Iowa State University, Ames, IA 50011, USA.
3. Plant Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
4. Genomic Analysis Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
5. Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE 68583, USA.
6. Howard Hughes Medical Institute, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA.