Abstract
The tobacco mosaic virus (TMV) movement protein (MP) required for the cell-to-cell spread of viral RNA interacts with the endoplasmic reticulum (ER) as well as with the cytoskeleton during infection. Whereas associations of MP with ER and microtubules have been intensely investigated, research on the role of actin has been rather scarce. We demonstrate that Nicotiana benthamiana plants transgenic for the actin-binding domain 2 of Arabidopsis (Arabidopsis thaliana) fimbrin (AtFIM1) fused to green fluorescent protein (ABD2:GFP) exhibit a dynamic ABD2:GFP-labeled actin cytoskeleton and myosin-dependent Golgi trafficking. These plants also support the movement of TMV. In contrast, both myosin-dependent Golgi trafficking and TMV movement are dominantly inhibited when ABD2:GFP is expressed transiently. Inhibition is mediated through binding of ABD2:GFP to actin filaments, since TMV movement is restored upon disruption of the ABD2:GFP-labeled actin network with latrunculin B. Latrunculin B shows no significant effect on the spread of TMV infection in either wild-type plants or ABD2:GFP transgenic plants under our treatment conditions. We did not observe any binding of MP along the length of actin filaments. Collectively, these observations demonstrate that TMV movement does not require an intact actomyosin system. Nevertheless, actin-binding proteins appear to have the potential to exert control over TMV movement through the inhibition of myosin-associated protein trafficking along the ER membrane.
Highlights
The tobacco mosaic virus (TMV) movement protein (MP) required for the cell-to-cell spread of viral RNA interacts with the endoplasmic reticulum (ER) as well as with the cytoskeleton during infection
Actin filaments were effectively visualized in agroinfiltrated Nicotiana benthamiana leaves, where the coexpression of actin-binding domain 2 (ABD2):GFP with ABD2 fused to red fluorescent protein (ABD2: RFP) resulted in exactly coinciding patterns of greenand red-labeled filaments (Fig. 1, F–H)
The pattern of actin filaments in agroinfiltrated leaf tissues was similar to the pattern detected in ABD2:GFP transgenic plants (Fig. 1, I–M); the fluorescence emitted from ABD2:GFP in the agrotransfected tissues increased over time
Summary
The tobacco mosaic virus (TMV) movement protein (MP) required for the cell-to-cell spread of viral RNA interacts with the endoplasmic reticulum (ER) as well as with the cytoskeleton during infection. We demonstrate that Nicotiana benthamiana plants transgenic for the actin-binding domain 2 of Arabidopsis (Arabidopsis thaliana) fimbrin (AtFIM1) fused to green fluorescent protein (ABD2:GFP) exhibit a dynamic ABD2:GFP-labeled actin cytoskeleton and myosin-dependent Golgi trafficking These plants support the movement of TMV. ER membranes are continuous between cells through PD (Ding et al, 1992b; Heinlein and Epel, 2004) and represent a potential pathway for the movement of membrane-associated replication complexes from the infected cells into adjacent cells This model of TMV movement is supported by observations indicating that ER membrane proteins can laterally diffuse within the membrane (Runions et al, 2006; GuenouneGelbart et al, 2008) and move from cell to cell (Guenoune-Gelbart et al, 2008)
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