The cytoskeleton and the secretory pathway are not involved in targeting the cowpea mosaic virus movement protein to the cell periphery

The movement protein (MP) of cowpea mosaic virus (CPMV) forms tubules on infected protoplasts and through plasmodesmata in infected plants. In protoplasts the MP fused to GFP (MP-GFP) was shown to localize in peripheral punctate structures and in long tubular structures extending from the protoplast surface. Using cytoskeletal assembly inhibitors (latrunculin B and oryzalin) and an inhibitor of the secretory pathway (brefeldin A), targeting of the MP to the peripheral punctate structures was demonstrated not to be dependent on an intact cytoskeleton or functional secretion pathway. Furthermore it was shown that a disrupted cytoskeleton had no effect on tubule formation but that the addition of brefeldin A severely inhibited tubule formation. The results presented in this paper suggest a role for a plasma membrane host factor in tubule formation of plant viral MPs.