1. Department of Plant Biology (W.F.B., H.W.S., Y.J.I., I.Y.P.) and Department of Microbiology (A.M.G.), North Carolina State University, Raleigh, North Carolina, 27695; Robert H. Smith Institute for Plant Sciences and Genetics in Agriculture, Robert H. Smith Faculty of Agriculture, Food and Environment, Hebrew University of Jerusalem, Rehovot 76100, Israel (N.M.)