DEFECTIVE MOVEMENT OF VIRUSES IN THE FAMILY BROMOVIRIDAE IS DIFFERENTIALLY COMPLEMENTED IN NICOTIANA-BENTHAMIANA EXPRESSING TOBAMOVIRUS OR DIANTHOVIRUS MOVEMENT PROTEINS

Taxonomically distinct tobacco mosaic tobamovirus (TMV), red clover ne crotic mosaic dianthovirus (RCNMV), cucumber mosaic cucumovirus (CMV), brome mosaic bromovirus (BMV), and cowpea chlorotic mottle bromovirus (CCMV) exhibit differences in their host range. Each of these viruses encodes a functionally similar nonstructural movement protein (MP) th at is essential for cell-to-cell movement of a progeny virus. Despite the lack of significant amino acid identity among the MPs of CMV, TMV, and RCNMV, movement-defective CMV (CMVFny Delta MP-Delta KPN) was abl e to move locally and systemically in transgenic Nicotiana benthamiana expressing either TMV MP (NB-TMV-MP(+)) or RCNMV MP (NB-RCNMV-MP(+)). These observations contrast with those of previous studies in which t ransgenic N. tabacum cv. Xanthi plants expressing TMV MP supported onl y the cell-to-cell movement of CMVFny Delta MP-Delta KPN. To verify wh ether similar complementation could be observed for movement-defective bromoviruses, NB-TMV-MP(+) and NB-RCNMV-MP(+) plants were inoculated independently with movement-defective variants of BMV (B3 Delta MP) an d CCMV (CC3 Delta MP). Neither NB-TMV-MP(+) nor NB-RCNMV-MP(+) was abl e to rescue the defective cell-to-cell and long-distance movement of B 3 Delta MP. In contrast, NB-RCNMV-MP(+) complemented the cell-to-cell, but not the long-distance, movement of CC3 Delta MP. Taken together, these studies suggest that virus movement is a complex process and tha t, in some cases, the host species plays a major role in determining t he long-distance movement function of a virus.