Movement in the infected plant
TMV uses its movement protein to spread from cell-to-cell through plasmodesmata, which connect plant cells (figure 10). Normally, the plasmodesmata are too small for passage of intact TMV particles.
The movement protein (probably with the assistance of as yet unidentified host proteins) enlarges the plasmodesmatal openings so that TMV RNA can move to the adjacent cells, release the movement protein and host proteins, and initiate a new round of infection. As the virus moves from cell to cell, it eventually reaches the plant's vascular system (veins) for rapid systemic spread through the phloem to the roots and tips of the growing plant.