Plays an essential role in cell-to-cell movement and long-distance transport of the viral genome. Mechanistically, movement protein is recruited by viral replicase complexes formed on RNA1 to punctate structures on the host cortical endoplasmic reticulum. In turn, interacts with the viral genome and mediates virion movement from cell to cell. Acts also as a suppressor of RNA-mediated gene silencing, also known as post-transcriptional gene silencing (PTGS), a mechanism of plant viral defense that limits the accumulation of viral RNAs. Interacts with host glyceraldehyde 3-phosphate dehydrogenase-A/NbGAPDH-A; this interaction plays a positive role in cell-to-cell movement of the virus. Targeting of virus movement protein to the host endoplasmic reticulum membrane is associated with the replication of viral RNA-1 but not that of RNA-2. The C-terminal domain is essential for localization to cortical punctate structures at an early stage of infection.