Mutational analysis of the cowpea mosaic virus movement protein

Cowpea mosaic virus moves from cell-to-cell in a virion form through tubula r structures that are assembled in modified plasmodesmata. Similar tubular structures are formed on the surface of protoplasts inoculated with cowpea mosaic virus. The RNA 2-encoded movement protein (MP) is responsible for th e induction and formation of these structures. To define functional domains of the MP, an alanine-substitution mutagenesis was performed on eight posi tions in the MP, including two conserved sequence motifs, the LPL and D mot ifs. Results show that these two conserved motifs as well as the central re gion of the MP are essential for cell-to-cell movement. Several viruses car rying mutations in the N- or C-terminal parts of their MP retained infectiv ity on cowpea plants. Coexpression studies revealed that mutant MPs did not interfere with the activity of wild-type MP and could not: mutually comple ment their defects. (C) 2000 Academic Press.