Cucumovirus- and bromovirus-encoded movement functions potentiate cell-to-cell movement of tobamo- and potexviruses

Abstract

Cucumber mosaic virus (CMV, a cucumovirus) and Brome mosaic virus (BMV, a bromovirus) require the coat protein (CP) in addition to the 3a movement protein (MP) for cell-to-cell movement, while Cowpea chlorotic mottle virus (CCMV, a bromovirus) does not. Using bombardment-mediated transcomplementation assays, we investigated whether the movement functions encoded by these viruses potentiate cell-to-cell movement of movement-defective Tomato mosaic virus (ToMV, a tobamovirus) and Potato virus X (PVX, a potexvirus) mutants in Nicotiana benthamiana. Coexpression of CMV 3a and CP, but neither protein alone, complemented the defective movement of ToMV and PVX. A C-terminal deletion in CMV 3a (3a Delta C33) abolished the requirement of CP in transporting the ToMV genome. The action of 3a Delta C33 was inhibited by coexpression of wild-type 3a. These findings were confirmed in tobacco with ToMV-CMV chimeric viruses. Either BMV 3a or CCMV 3a alone efficiently complemented the movement-defective phenotype of the ToMV mutant. Therefore, every 3a protein examined intrinsically possesses the activity required to act as MP. In transcomplementation of the PVX mutant, the activities of BMV 3a, CCMV 3a, and CMV 3a Delta C33 were very low. The activities of the bromovirus 3a proteins were enhanced by coexpression of the cognate CP but the activity of CMV 3a Delta C33 was not. Based on these results, possible roles of cucumo- and bromovirus CPs in cell-to-cell movement are discussed.

The influence of the N- and C- terminal modifications of Potato virus X coat protein on virus properties

“…It was also confirmed that the cellto-cell movement of Potato virus X can be compensated by the TMV MP as published previously (Fedorkin et al 2001, Tamai et al 2003. However, the C-terminus of the XCP probably plays a role in the particle assembly and assembly-deficient virus failed to move into systemic leaves in N. benthamiana MP.…”

Suppression of local RNA silencing is not sufficient to promote cell-to-cell movement ofTurnip crinkle virusinNicotiana benthamiana

“…18 Cucumovirus-and bromovirus-encoded movement functions facilitate the cell-to-cell movement of tobamo-and potex-viruses. 19 Tobamo-and potex-viruses can also complement each other in their cell-to-cell and long-distance movement functions. 20 Plant viral silencing suppressors possess diverse amino acid sequences and target various stages of RNA silencing.…”

Cellular pathways for viral transport through plasmodesmata

“…Interestingly, seemingly similar structures are formed in TMV-infected protoplasts suggesting that even TMV, the paradigm for non-tubule-mediated transport of viral ribonucleoprotein complexes (vRNPs), may have the option for different movement strategies (Heinlein et al 1998a). Common biochemical properties and flexible movement strategies may contribute to the ability of MPs to complement the movement deficiency of unrelated viruses (Lewandowski and Adkins 2005;Morozov et al 1997;Rao et al 1998;Sanchez-Navarro et al 2006;Tamai et al 2003). …”