Requirement of the movement protein for long distance spread of tobacco mosaic virus in grafted plants

Systemic spread of tobacco mosaic virus (TMV) that lacks a functional movement protein (TMV Delta MP) was investigated in grafted tobacco (Nicotiana tabacum) plants, Transgenic plants that express the 30-kDa movement protein (MP) gene (MP) under the control of the rolC (phloem-specific) or pal2 (xylem-specific) promoters were unable to support systemic infection by the mutant virus, while plants that express the MP gene from the cauliflower mosaic virus 35S promoter (35S:MP) led to systemic infection, Doubly grafted plants were constructed in which plants containing the 35S:MP gene were used as root stock and plants carrying various MP constructs constituted the middle scion, The upper scion contained the 35S:MP gene in plants that produce a hypersensitive response when systemically infected by TMV, TMV Delta MP moved systemically and produced complete necrosis in the upper scion when expression of MP in the middle scion was under the control of the rolC or 35S promoter, but not when the pal2 promoter was used, When plants expressing a gene encoding a defective MP were used as the middle scion, there was no systemic infection by TMV Delta MP, and a delay in systemic infection by wild-type TMV, In grafted plants with middle scions that expressed the TMV 54 kDa gene sequence there was no apparent systemic infection by TMV Delta MP in the upper scion, The results obtained indicate that the MP has a role in long distance movement, and support the suggestion that replication is necessary for systemic infection of these grafted plants.