Cucumovirus- and bromovirus-encoded movement functions potentiate cell-to-cell movement of tobamo- and potexviruses.
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.
Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Atsushi
A
Tamai
Kenji
K
Kubota
Hideaki
H
Nagano
Motoyasu
M
Yoshii
Masayuki
M
Ishikawa
Kazuyuki
K
Mise
Tetsuo
T
Meshi
D001483:Base Sequence; D017795:Bromovirus / Q000235:genetics* / Q000378:metabolism; D036022:Capsid Proteins / Q000235:genetics / Q000378:metabolism; D017799:Cucumovirus / Q000235:genetics* / Q000378:metabolism; D015967:Gene Expression Regulation, Viral; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018551:Solanum lycopersicum / Q000821:virology; D008969:Molecular Sequence Data; D010935:Plant Diseases / Q000821:virology*; D018515:Plant Leaves / Q000821:virology; D053830:Plant Viral Movement Proteins; D017863:Potexvirus / Q000502:physiology*; D011993:Recombinant Fusion Proteins; D014026:Nicotiana / Q000821:virology; D017898:Tobamovirus / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D036022:Capsid Proteins; D008164:Luminescent Proteins; D053830:Plant Viral Movement Proteins; D011993:Recombinant Fusion Proteins; D014764:Viral Proteins; D049452:Green Fluorescent Proteins