1. Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
2. Computational Biology Department, School of Computer Science, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
3. Genomic Analysis Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
4. Howard Hughes Medical Institute (HHMI), Salk Institute for Biological Studies, La Jolla, CA 92037, USA.