Abstract
Studies during the last 25 years have provided increasing evidence for the ability of plants to support the cell-to-cell and systemic transport of RNA molecules and that this process plays a role in plant development and in the systemic orchestration of cellular responses against pathogens and other environmental challenges. Since RNA viruses exploit the cellular RNA transport machineries for spreading their genomes between cells they represent convenient models to investigate the underlying mechanisms. In this regard, the intercellular spread of Tobacco mosaic virus (TMV) has been studied for many years. The RNA of TMV moves cell-to-cell in a non-encapsidated form in a process depending on virus-encoded movement protein (MP). Here, we discuss the current state of the art in studies using TMV and its MP as a model for RNA transport. While the ability of plants to transport viral and cellular RNA molecules is consistent with RNA transport phenomena in other systems, further studies are needed to increase our ability to visualize viral RNA (vRNA) in vivo and to distinguish RNA-transport related processes from those involved in antiviral defense.
Highlights
Tobacco mosaic virus (TMV) is a rod-shaped virus with a positivesensed RNA genome that encodes 126 kD and 183 kD subunits of replicase, a 30 kD movement protein (MP) and a 17.5 kD coat protein (CP)
Based on experimental evidence suggesting that the replicase is involved in virus movement (Hirashima and Watanabe, 2001; Guenoune-Gelbart et al, 2008) and that the virus moves in the form of replication complexes (Kawakami et al, 2004), the vRNP may be associated with several viral and host proteins in addition to viral RNA (vRNA) and MP
(≥3 days), either by exposure to actin or myosin antagonists, or by silencing actin or myosin expression (Kawakami et al, 2004; Liu et al, 2005; Harries et al, 2009a,b). In this case, it remains to be seen whether this result implies a direct role of actin and myosin in viral replication complexes (VRC) transport along the endoplasmic reticulum (ER) membrane or whether this observation could be explained by indirect effects, for example by compromising the role of the actin cytoskeleton in maintaining the dynamic structural integrity of the ER (Wright et al, 2007; Hofmann et al, 2009; Sparkes et al, 2009b)
Summary
Tobacco mosaic virus (TMV) is a rod-shaped virus with a positivesensed RNA genome that encodes 126 kD and 183 kD subunits of replicase, a 30 kD movement protein (MP) and a 17.5 kD coat protein (CP). The virus provides a valuable tool to study RNA transport as the spread of infection does not require CP and the vRNA moves cell-to-cell in a nonencapsidated form.
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