Plant virus-specific transport function. I. Virus genetic control required for systemic spread.
Complementation of tobacco mosaic virus (TMV) mutant LS1 which is temperature-sensitive (ts) in virus transport function was studied in two model systems. The first one was aimed at complementing LS1 cell-to-cell spread through the tissues of the plant systemically preinfected with a temperature-resistant (tr) virus. Two different experiments were performed in this model system. (a) Use was made of a host plant which reacted differently to LS1 (local lesions) and to the helper virus (systemic reaction) at a permissive (24 degrees) temperature. Complementation occurred in a mixedly infected plant at a temperature which is nonpermissive for LS1 (32 degrees), when the necrotic reaction of the host was switched off; the complementation could be revealed upon the temperature shift treatment (TST) (24 --> 32 --> 24 degrees ). (b) Transport of LS1 from cell to cell in the presence of the helper virus was tested directly by immunofluorescent microscopy. In the second model system, the effect of virus transport from the conducting tissues of the stem into the cells of the leaf mesophyll, preinfected with the helper virus, was studied. It was shown that ts mutant LS1, imbibed through the stem, can move into and replicate in the mesophyll cells of the leaf which was preinfected with a tr-helper virus. This was true both at 24 and 32 degrees . On the other hand, LS1 itself could serve as a helper virus only at 24, but not at 32 degrees . In both model systems, it was demonstrated that ts transport can be complemented not only by a related tr TMV strain, but also by an unrelated virus-potato virus X. It has been suggested that a virus-specific transport function performed by the helper virus "opens the gates" for the dependent virus by an unknown modification of host cells.
Taliansky
M E
ME
Department of Virology and A. N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, Moscow 117234, USSR.
Malyshenko
S I
SI
Pshennikova
E S
ES
Kaplan
I B
IB
Ulanova
E F
EF
Atabekov
J G
JG