1. Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305 (E.M., N.d.K., H.-I.N., K.P., S.Y.R.);
2. Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique Centre de Versailles-Grignon, 78026 Versailles Cedex, France (E.M., E.F.); and
3. Department of Biology, Stanford University, Stanford, California 94305 (J.-G.K., M.B.M.)