TOBAMOVIRUS AND DIANTHOVIRUS MOVEMENT PROTEINS ARE FUNCTIONALLY HOMOLOGOUS

The movement proteins (MPs) of tobacco mosaic tobamovirus (TMV) and re d clover necrotic mosaic dianthovirus (RCNMV) enlarge plasmodesmata si ze exclusion limits, transport RNA from cell to cell, and bind nucleic acids in vitro. Despite these functional similarities, they have no s equence homology. However, they do appear to have similar secondary st ructures. We have used transgenic plants expressing either the TMV MP or the RCNMV MP, and a chimeric TMV that encodes the RCNMV MP as its o nly functional MP gene, to demonstrate that the MPs of TMV and RCNMV a re functionally homologous. Further, both TMV and RCNMV can act as hel per viruses to allow the cell-to-cell movement of the heterologous mov ement-defective viruses. These data support the conclusion that, despi te other differences, such as particle morphology, host range, and seq uence, TMV and RCNMV share a common mechanism for cell-to-cell movemen t. (C) 1995 Academic Press, Inc.