THE PLANT CELL, Vol 2, Issue 6 559-567, Copyright © 1990 by American Society of Plant Biologists
Local and Systemic Spread of Tobacco Mosaic Virus in Transgenic Tobacco
L. A. Wisniewski, P. A. Powell, R. S. Nelson and R. N. Beachy
Biology Department, Washington University, St. Louis, Missouri 63130
Expression of a chimeric gene encoding the coat protein (CP) of tobacco
mosaic virus (TMV) in transgenic tobacco plants confers resistance to
infection by TMV. We investigated the spread of TMV within the inoculated
leaf and throughout the plant following inoculation. Plants that expressed
the CP gene [CP(+)] and those that did not [CP(-)] accumulated equivalent
amounts of virus in the inoculated leaves after inoculation with TMV-RNA,
but the CP(+) plants showed a delay in the development of systemic symptoms
and reduced virus accumulation in the upper leaves. Tissue printing
experiments demonstrated that if TMV infection became systemic, spread of
virus occurred in the CP(+) plants essentially as it occurred in the CP(-)
plants although at a reduced rate. Through a series of grafting
experiments, we showed that stem tissue with a leaf attached taken from
CP(+) plants prevented the systemic spread of virus. Stem tissue without a
leaf had no effect on TMV spread. All of these findings indicate that
protection against systemic spread in CP(+) plants is caused by one or more
mechanisms that, in correlation with the protection against initial
infection upon inoculation, result in a phenotype of resistance to TMV.
