Functional similarities between plant virus movement proteins and approaches to creating transgenic plants that restrict viral movement

Many different plant viruses encode the ability to move from cell-to-cell through cellular plasmodesmatal boundaries. This function is attributed to the viral movement protein (MP). Because a great many viruses share similar cell-to-cell movement functions, engineered interference with viral movement is a mechanism by which multivirus resistance can be obtained in transgenic plants. Transgenic plants that express a tobacco mosaic tobamovirus (TMV) MP gene engineered to be dysfunctional were resistant to the infection of TMV, tobacco rattle tobravirus, peanut chlorotic streak caulimovirus, tobacco ringspot nepovirus, alfalfa mosaic alfamovirus and cucumber mosaic cucumovirus (CMV). Conversely, the expression of a functional TMV MP gene in transgenic plants enhanced symptoms and/or increased the accumulation of the same viruses. These studies contribute to the understanding of a multivirus resistance mechanism that blocks viral movement and reveal that synergistic viral infections can be caused by MPs.;While broad, the analysis of MPs and their interactions with components of the plant cell are incongruous. In an attempt to unite the broad generalizations previously made for two MPs, the subcellular localization of the TMV and CMV MPs from transgenic and infected tissue was examined using a single fractionation method. Transgenic TMV and CMV MPs were found in the cell wall subcellular fractions whereas, in infected tissue, the TMV MP was detected in the organelle fraction and the CMV MP was detected in fractions containing the detergent soluble components of the cell wall. This simple study shows common biological characteristics of the MPs, but it also resolves unique traits that contribute to the identities of the viral MPs themselves.;Finally, the complementary effects of the TMV and CMV MPs on the opposing viral genomes were examined. Transgenic plants that expressed a CMV MP gene could not complement the cell-to-cell movement of a movement-defective TMV. However, transgenic plants that expressed a TMV MP gene could complement the cell-to-cell movement of a movement-defective CMV. This study may help predict the extent to which MPs will be most effective in achieving the broadest and most effective form of resistance that blocks a movement mechanism that most viruses share.