1. Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan
2. Japan Science and Technology Agency, PRESTO, Kawaguchi-shi, Saitama 332-0012, Japan
3. Genome Center and Department of Plant Biology, University of California, Davis, California 95616
4. Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan