Lapidot, M., Department of Cell Biology, Scripps Research Institute, San Diego, CA 92037, United States
Gafny, R., Department of Cell Biology, Scripps Research Institute, San Diego, CA 92037, United States, Department of Virology, Volcani Center, Box 6, Bet Dagan 50250, Israel
Ding, B., Botany Department, University of California, Davis, CA 95616, United States
Wolf, S., Botany Department, University of California, Davis, CA 95616, United States, Department of Vegetable Crops, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot 76100, Israel
Lucas, W.J., Botany Department, University of California, Davis, CA 95616, United States
Beachy, R.N., Department of Cell Biology, Scripps Research Institute, San Diego, CA 92037, United States

A chimeric gene encoding a dysfunctional tobacco mosaic virus (TMV) movement protein (MP) mutant lacking amino acids 3, 4 and 5 (MPΔ3-5), was expressed in transgenic Nicotlana tabacum Xanthi and Xanthi NN plants. Immunogold labeling studies of tissues from transgenic plants indicated that while wild-type MP accumulated in the plasmodesmata, MPΔ3-5 did not. Tissue fractionation studies confirmed that only a low level of the mutant MP accumulated in the cell wall-enriched fraction compared with the accumulation of the wild-type MP. Dye coupling studies showed that MPΔ3-5 enabled the movement between leaf mesophyll cells of a fluorescently labeled dextran of 3 kDa, while 9.4 kDa molecules failed to move. In contrast, in transgenic plants expressing the wild-type MP gene the 9.4 kDa probe did move from cell to cell. Seedlings from self-fertilized transgenic plants were inoculated with TMV and observed for disease symptoms. Transgenic Xanthi NN plants that expressed the MPΔ3-5gene developed fewer and smaller necrotic local lesions compared with control plants following inoculation with TMV. Transgenic Xanthi nn plants were delayed in the development of systemic symptoms. Inoculating the transgenic plants with TMV-RNA, and the tobamo-viruses TMGMV and SHMV, essentially produced the same results, i.e. inhibition of disease development. These results demonstrate that transgenic plants expressing an inactive MP can inhibit virus disease spread presumably by interfering with its cell-to-cell movement.