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Transient Coexpression of Individual Genes Encoded by the Triple Gene Block of Potato mop-top virus Reveals Requirements for TGBp1 Trafficking

August 2004 , Volume 17 , Number  8
Pages  921 - 930

Andrey A. Zamyatnin , Jr. , 1 Andrey G. Solovyev , 2 Eugene I. Savenkov , 1 Anna Germundsson , 1 Maria Sandgren , 1 Jari P. T. Valkonen , 1 , 3 and Sergey Y. Morozov 2

1Department of Plant Biology and Forest Genetics, Swedish University of Agricultural Sciences (SLU), SE-750 07 Uppsala, Sweden; 2A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia; 3Department of Applied Biology, University of Helsinki, Finland

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Accepted 13 April 2004.

TGBp1, TGBp2, and TGBp3, three plant virus movement proteins encoded by the “triple gene block” (TGB), may act in concert to facilitate cell-to-cell transport of viral RNA genomes. Transient expression of Potato mop-top virus (genus Pomovirus) movement proteins was used as a model to reconstruct interactions between TGB proteins. In bombarded epidermal cells of Nicotiana benthamiana, green fluorescent protein (GFP)-TGBp1 was distributed uniformly. However, in the presence of TGBp2 and TGBp3, GFP-TGBp1 was directed to intermediate bodies at the cell periphery, and to cell wall-embedded punctate bodies. Moreover, GFP-TGBp1 migrated into cells immediately adjacent to the bombarded cell. These data suggest that TGBp2 and TGBp3 mediate transport of GFP-TGBp1 to and through plasmodesmata. Mutagenesis of TGBp1 suggested that the NTPase and helicase activities of TGBp1 were not required for its transport to intermediate bodies directed by TGBp2 and TGBp3, but these activities were essential for the protein association with cell wall-embedded punctate bodies and translocation of TGBp1 to neighboring cells. The C-terminal region of TGBp1 was critical for trafficking mediated by TGBp2 and TGBp3. Mutation analysis also suggested an involvement of the TGBp2 C-terminal region in interactions with TGBp1.

Additional keywords: cell-to-cell movement, intracellular trafficking.

© 2004 The American Phytopathological Society