Turnip mosaic virus NIb weakens the function of eukaryotic translation initiation factor 6 facilitating viral infection in Nicotiana benthamiana.

Viruses rely completely on host translational machinery to produce the proteins encoded by their genes. Controlling translation initiation is important for gaining translational advantage in conflicts between the host and virus. The eukaryotic translation initiation factor 4E (eIF4E) has been reported to be hijacked by potyviruses for virus multiplication. The role of translation regulation in defence and anti-defence between plants and viruses is not well understood. We report that the transcript level of eIF6 was markedly increased in turnip mosaic virus (TuMV)-infected Nicotiana benthamiana. TuMV infection was impaired by overexpression of N. benthamiana eIF6 (NbeIF6) either transiently expressed in leaves or stably expressed in transgenic plants. Polysome profile assays showed that overexpression of NbeIF6 caused the accumulation of 40S and 60S ribosomal subunits, the reduction of polysomes, and also compromised TuMV UTR-mediated translation, indicating a defence role for upregulated NbeIF6 during TuMV infection. However, the polysome profile in TuMV-infected leaves was not identical to that in leaves overexpressing NbeIF6. Further analysis showed that TuMV NIb protein, the RNA-dependent RNA polymerase, interacted with NbeIF6 and interfered with its effect on the ribosomal subunits, suggesting that NIb might have a counterdefence role. The results propose a possible regulatory mechanism at the translation level during plant-virus interaction.