Complementation of the movement-deficient mutations in potato virus X: potyvirus coat protein mediates cell-to-cell trafficking of C-terminal truncation but not deletion mutant of potexvirus coat protein.

The cell-to-cell movement of the GUS-tagged potato virus X (PVX) coat protein (CP) movement-deficient mutant was restored by potyviral CPs of potato virus A (PVA) and potato virus Y (PVY) in Nicotiana benthamiana leaves in transient cobombardment experiments. Viral cell-to-cell movement of PVX CP mutant was complemented in Nicotiana tabacum cv. SR1 transgenic plants expressing PVY CP: PVX RNA and polymerase were detected in the PVX CP mutant-inoculated leaves of transgenic plants. These findings demonstrated the ability of the PVX CP-deficient mutant to move from cell to cell but not long distances in the transgenic plants and suggest that CPs of potex- and potyviruses display complementary activities in the movement process. Potyviral CP alone is not able to carry out these activities, since the mutated PVX CP is indispensable for restored movement. No trans-encapsidation between potyviral CP and PVX RNA was observed. Therefore, potyviral CP facilitates the PVX CP mutant movement by the mechanism that cannot be explained by coat protein substitution. Our data also suggest that CP functioning in cell-to-cell movement is not restricted to a simple passive role in forming virions.