Intracellular and intercellular movement of maize streak geminivirus V1 and V2 proteins transiently expressed as green fluorescent protein fusions

Transient expression of the maize streak geminivirus virion-sense proteins V1 and V2 (movement protein, MP, and coat protein, CP, respectively) in mai ze leaves allowed investigation of their roles in inter- and intracellular movement. Bombardment of a construct directing expression of a V1:green flu orescent protein (GFP) fusion product resulted in significantly increased s pread of fluorescence from the bombarded cell to adjacent cells compared to that obtained following expression of free GFP. A mutant V1:GFP fusion pro duct exhibited markedly less movement than the V1:GFP protein. Thus, the MS V V1 protein moves from cell to cell in the absence of other viral proteins . However, V1:GFP did not localize to plasmodesmata in maize or tobacco lea ves although a tobacco mosaic virus MP:GFP fusion protein was shown to do s o in tobacco. The CP:GFP fusion product targeted exclusively to the nucleus and did not move from cell to cell or exit the nucleus when expressed alon e. When coexpressed with V1, some CP:GFP fluorescence was seen at the cell periphery in a proportion of cells, but in no case was cell-to-cell movemen t of CP:GFP detected. The likely roles of V1 and CP in MSV movement are dis cussed. (C) 2000 Academic Press.