The Rice stripe virus (RSV) pc4 has been determined as the viral movement protein (MP). In this study, the pc4 gene was cloned into a movement-deficient Tobacco mosaic virus (TMV). The resulting hybrid TMV-pc4, in addition to spreading cell to cell in Nicotiana tabacum, moved systemically and induced foliar necrosis in Nicotiana benthamiana, indicating novel functions of the RSV MP. A systematic alanine-scanning mutagenesis study established the region K(122)-D(258) of the pc4 substantially associated with cell-to-cell movement, and mutants by replacement of KGR(122-124), D(135), ED(170-171), ER(201-202), EFE(218-220) or ELD(256-258) with alanine(s) no longer moved cell to cell. However, only one amino acid group KGR(122-124) was linked with long-distance movement. The region D(17)-K(33) was recognized as a crucial domain for leaf necrosis response, and mutagenesis of DD(17-18) or RK(32-33) greatly attenuated necrosis. The overall data suggested manifold roles of the pc4 during the RSV infection in its experimental host N. benthamiana.
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