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The N-Terminal Domain of PMTV TGB1 Movement Protein Is Required for Nucleolar Localization, Microtubule Association, and Long-Distance Movement

November 2010 , Volume 23 , Number  11
Pages  1,486 - 1,497

Kathryn M. Wright,1 Graham H. Cowan,1 Nina I. Lukhovitskaya,2 Jens Tilsner,1 Alison G. Roberts,1 Eugene I. Savenkov,2 and Lesley Torrance1

1Plant Pathology Programme, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, U.K.; 2Department of Plant Biology and Forest Genetics, Uppsala BioCenter SLU, Box 7080, SE-750 07 Uppsala, Sweden

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Accepted 11 June 2010.

The triple-gene-block (TGB)1 protein of Potato mop-top virus (PMTV) was fused to fluorescent proteins and expressed in epidermal cells of Nicotiana benthamiana under the control of the 35S promoter. TGB1 fluorescence was observed in the cytoplasm, nucleus, and nucleolus and occasionally associated with microtubules. When expressed from a modified virus (PMTV.YFP-TGB1) which formed local lesions but was not competent for systemic movement, yellow fluorescent protein (YFP)-TGB1 labeled plasmodesmata in cells at the leading edge of the lesion and plasmodesmata, microtubules, nuclei, and nucleoli in cells immediately behind the leading edge. Deletion of 84 amino acids from the N-terminus of unlabeled TGB1 within the PMTV genome abolished movement of viral RNA to noninoculated leaves. When the same deletion was introduced into PMTV.YFP-TGB1, labeling of microtubules and nucleoli was abolished. The N-terminal 84 amino acids of TGB1 were fused to green fluorescent protein (GFP) and expressed in epidermal cells where GFP localized strongly to the nucleolus (not seen with unfused GFP), indicating that these amino acids contain a nucleolar localization signal; the fusion protein did not label microtubules. This is the first report of nucleolar and microtubule association of a TGB movement protein. The results suggest that PMTV TGB1 requires interaction with nuclear components and, possibly, microtubules for long-distance movement of viral RNA.

© 2010 The American Phytopathological Society