1. Department of Plant Sciences, Hebrew University of Jerusalem, Jerusalem, Givat-Ram 91904, Israel (T.S.P., A.L.)
2. Department of Microbiology and Molecular Genetics, University of Vermont, 202 Stafford Hall, Burlington, Vermont 05405 (C.C.C., D.I.J.)
3. Section of Plant Biology, University of California, One Shields Avenue, Davis, California 95616–8537 (D.P.D.)