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Cell-to-Cell Movement of Potexviruses: Evidence for a Ribonucleoprotein Complex Involving the Coat Protein and First Triple Gene Block Protein

September 2000 , Volume 13 , Number  9
Pages  962 - 974

Tony J. Lough , 1 , 3 Natalie E. Netzler , 1 Sarah J. Emerson , 1 Paul Sutherland , 1 Fiona Carr , 2 David L. Beck , 1 William J. Lucas , 1 , 3 and Richard L. S. Forster 1

1Horticulture and Food Research Institute of New Zealand, Plant Health and Development Group, Private Bag 92 169, Auckland, New Zealand; 2Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, U.K.; 3Section of Plant Biology, Division of Biological Sciences, University of California, Davis 95616, U.S.A.

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Accepted 11 May 2000.

The triple gene block proteins (TGBp1-3) and coat protein (CP) of potexviruses are required for cell-to-cell movement. Separate models have been proposed for inter-cellular movement of two of these viruses, transport of intact virions, or a ribonucleoprotein complex (RNP) comprising genomic RNA, TGBp1, and the CP. At issue therefore, is the form(s) in which RNA transport occurs and the roles of TGBp1-3 and the CP in movement. Evidence is presented that, based on microprojectile bombardment studies, TGBp1 and the CP, but not TGBp2 or TGBp3, are co-translocated between cells with viral RNA. In addition, cell-to-cell movement and encapsidation functions of the CP were shown to be separable, and the rate-limiting factor of potexvirus movement was shown not to be virion accumulation, but rather, the presence of TGBp1-3 and the CP in the infected cell. These findings are consistent with a common mode of transport for potex-viruses, involving a non-virion RNP, and show that TGBp1 is the movement protein, whereas TGBp2 and TGBp3 are either involved in intracellular transport or interact with the cellular machinery/docking sites at the plasmodesmata.

© 2000 The American Phytopathological Society