Cell-to-cell movement of the 25K protein of Potato virus X is regulated bythree other viral proteins

The 25K, 12K, and 8K proteins and coat protein (CP) of Potato virus X (PVX) are required for virus cell-to-cell movement. In this study, experiments w ere conducted to determine whether the PVX 25K: protein moves cell to cell and to explore potential interactions between the PVX 25K, 12K, and 8K prot eins acid CP. The PVX 25K gene was fused to the green fluorescent protein ( GFP) gene and inserted into plasmids adjacent to the cauliflower mosaic vir us 35S promoter, These plasmids were introduced by biolistic bombardment to transgenic tobacco expressing the PVX 12K, 8K, and CP genes. The GFP:25K f used proteins moved cell to cell on nontransgenic tobacco and tobacco expre ssing either the 12K or 8K proteins, However, the GFP:25K proteins did not move on transgenic tobacco expressing the combined 12K/8K genes or the CP g ene. Thus, movement of the PVX 25K protein through plasmodesmata may be reg ulated by interactions with other PVX proteins.