1. Division of Plant Sciences and National Center for Soybean Biotechnology (X.-C.Z., X.W., S.F., J.W., M.L., H.T.N., G.S.) and Division of Biochemistry, Department of Molecular Microbiology and Immunology (G.S.), University of Missouri, Columbia, Missouri 65211; and United States Department of Agriculture-Agricultural Research Service and Department of Agronomy, Iowa State University, Ames, Iowa 50