This work was supported in part by Grants-in-Aid from the Japan Society for the Promotion of Science (JSPS). We thank Drs I. Suzuki, Y. Shiraiwa, H. Ezura, and T. Mizoguchi (University of Tsukuba, Japan) and Dr. K. Sugimoto (National Institute of Agrobiological Sciences) for their technical suggestions. We thank Dr. S. Terakami (University of Tsukuba, Japan) for his technical assistance with the computational analysis.