Tobacco mosaic virus movement protein associates with the cytoskeleton in tobacco cells.

Abstract

Tobacco mosaic virus movement protein P30 complexes with genomic viral RNA for transport through plasmodesmata, the plant intercellular connections. Although most research with P30 focuses on its targeting to and gating of plasmodesmata, the mechanisms of P30 intracellular movement to plasmodesmata have not been defined. To examine P30 intracellular localization, we used tobacco protoplasts, which lack plasmodesmata, for transfection with plasmids carrying P30 coding sequences under a constitutive promoter and for infection with tobacco mosaic virus particles. In both systems, P30 appears as filaments that colocalize primarily with microtubules. To a lesser extent, P30 filaments colocalize with actin filaments, and in vitro experiments suggested that P30 can bind directly to actin and tubulin. This association of P30 with cytoskeletal elements may play a critical role in intracellular transport of the P30-viral RNA complex through the cytoplasm to and possibly through plasmodesmata.

Cell-cell interactions during plant development.

“…Similar conclusions were reached by antibody colocalization of the P30 movement protein and microtubule proteins in protoplasts, as well as by in vitro binding studies (McLean et al 1995). Colocalization of actin and P30 was also documented, but to a lesser degree (McLean et al 1995). Support for an association of actin with plasmodesmata comes from the finding that the SEL is increased following injections of actin inhibitors such as cytochalasin D (Ding et al 1996).…”

“…Similar conclusions were reached by antibody colocalization of the P30 movement protein and microtubule proteins in protoplasts, as well as by in vitro binding studies (McLean et al 1995). Colocalization of actin and P30 was also documented, but to a lesser degree (McLean et al 1995).…”

Tobacco mosaic virus: a pioneer to cell–to–cell movement

“…How, then, do these complexes arrive at plasmodesmata prior to cell-tocell movement ? Recent data suggest that P30 interacts with microtubules and, to a lesser extent, with actin micro¢laments (Heinlein et al 1995;McLean et al 1995). This interaction was inferred from colocalization of P30, transiently expressed in tobacco protoplasts, with tubulin as well as with actin ¢laments (McLean et al 1995).…”

“…To date, four biological activities have been postulated for P30: (i) binding to TMV RNA, forming an extended P30-RNA complex that can penetrate the plasmodesmatal channel (Citovsky et al 1990(Citovsky et al , 1992a; (ii) interacting with cytoskeletal elements to facilitate transport of the P30-TMV RNA complexes from the cell cytoplasm to plasmodesmata (Heinlein et al 1995;McLean et al 1995); (iii) increasing the size exclusion limit of plasmodesmata (Wolf et al 1989); and (iv) interacting with a cell-wall-associated receptor, which then phosphorylates the bound movement protein, inactivating its ability to dilate plasmodesmata. Here, we examine these P30 activities and integrate them into a model for P30-mediated intercellular transport of TMV RNA.…”

Cell-to-cell movement of three genera (+) ss RNA plant viruses

“…If MP is incorporated in ER, cell-to-cell transport takes place via MP-vRNA complex diffusion to PD desmotubules lipid matrix under the action of concentration gradient between healthy and infected cells (LippincottSchwartz et al 2000;Runions et al 2006). The MP presence in ER or in ER vesicles as well as the relation with microtubules (Heinlein et al 1995) and microfilaments (McLean et al 1995) suggests that elements of the cytoskeleton are an important component engaged in the transport to PD and in cell-to-cell movement of the viral ribonucleic complex . Actins and myosins are present inside PD and are responsible for the ER membrane translocation (Blackman and Overall 1998;Yokota et al 2009).…”