To obtain evidence on the importance of eEF1Bc in TBSV replication in the natural plant hosts, we knocked down the expression of the eEF1Bc gene in Nicotiana bethamiana leaves via VIGS (virus-induced gene silencing). Efficient knocking down of eEF1Bc mRNA level in N. benthamiana ( Figure 7B ) only resulted in slightly reduced growth of the plants without other phenotypic effects ( Figure 7A ). The accumulation of TBSV genomic RNA, however, was dramatically reduced in both inoculated ( Figure 7B , lanes 1-5) and the systemically-infected young leaves ( Figure 7C , lanes 1-4) when compared with the control plants infected with the 'empty' Tobacco rattle virus (TRV) vector. The lethal necrotic symptoms caused by TBSV in N. benthamiana were also greatly attenuated in the eEF1Bc knock-down plants ( Figure 7A ). Therefore, we conclude that eEF1Bc is essential for TBSV genomic RNA accumulation in N. bethamiana.