1. Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037 (C.D., B.H., S.M.R., J.F.H.); Biology Department, Washington University, St. Louis, Missouri 63130–4899 (A.I., B.G.P.); Department of Plant Biology, University of New Hampshire, 46 College Road, Durham, New Hampshire 03824 (E.M.H.); and Botany Department, University of Florida, Gainesville, Florida 32611–8526 (