TMV Movement Protein Targets Cell-Cell Channels in Plants and Prokaryotes: Possible Roles of Tubulin- and FtsZ-Based Cytoskeletons
Cell-to-cell communication in plants occurs via plasmodesmata (Pd), dynamic membrane-lined pores in the plant cell wall that provide symplasmic continuity between adjacent cells. Communication through Pd involves the trafficking of protein and RNA macromolecules, and also includes the trafficking of viruses. Virus movement depends on virus-encoded movement proteins (MP), of which the MP of Tobacco mosaic virus (TMV) has been most thoroughly studied. The many cellular activities of this protein include the interaction with Pd, which results in the deposition of fibrous material in the Pd cavity as well as in an increased size-exclusion limit of the channel. The protein also interacts with plant microtubules and actin filaments, and the alignment of the protein to microtubules has been correlated with the function of this protein. Intriguingly, the protein also interacts with the cell junctions of the multicellular cyanobacterium Anabaena suggesting a degree of functional analogy between intercellular communication mechanisms of multicellular prokaryotes and plants. In Anabaena, MP induces the formation of MP-associated filaments which traverse the intercellular septa and which may be similar in nature to the fibrous MP-associated material localized to Pd in MP-expressing plants. These observations may suggest the involvement of conserved cytoskeletal elements in the MP-dependent modification and plasticity of intercellular connections in evolutionary divergent species.