Characterization of cucumber mosaic virus. IV. Movement protein and coat protein are both essential for cell-to-cell movement of cucumber mosaic virus.

摘要

The 3a movement protein (MP) and coat protein (CP) of the cucumber mosaic cucumovirus (CMV) are needed for viral movement from cell to cell. In order to further investigate their role, modified cDNA constructs of CMV RNA 3 which could express the jellyfish green fluorescent protein (GFP) were prepared. GFP was expressed in one of 3 ways: in place of either CP or MP; fused to either the N-terminal or the C-terminal of MP (designated GFP-MP and MP-GFP, respectively); or in addition to both CP and MP(i.e. from a separate open reading frame). The constructs were inoculated into Nicotiana benthamiana epidermis. Neither of the constructs in which CP or MP had been replaced were able to mediate cell-to-cell movement on their own, but were able to do sowhen co-expressed, suggesting that both proteins were essential for CMV movement. When the fusion proteins GFP-MP and MP-GFP were expressed in N. benthamiana or N. tabacum, fluorescence was restricted to single cells, although their distribution within the cells was different. MP-GFP was confined to the cell wall, while GFP-MP was scattered throughout the cytoplasm as well as associated with the cell wall. Cells were injected with 10 kDa fluorescent dextran in order to examine the ability of the inoculato increase plasmodesmatal permeability. Cells expressing MP plus free GFP, as well as those expressing MP-GFP (but not GFP-MP), showed movement of the dextran even though no viral movement was observed. It is suggested that the mechanism by which MP transports viral RNA is separate from that by which it transports other molecules.