Dissecting the role of a plant-specific Rab5 small GTPase NbRabF1 in Bamboo mosaic virus infection.

NbRabF1, a small GTPase from Nicotiana benthamiana and a homolog of Arabidopsis thaliana Ara6, plays a key role in regulating Bamboo mosaic virus (BaMV) movement by vesicle transport between endosomal membranes. Reducing the expression of NbRabF1 in N. benthamiana by virus-induced gene silencing decreased the accumulation of BaMV, and with smaller infection foci on inoculated leaves, but had no effect in protoplasts. Furthermore, transient expression of NbRabF1 increased the accumulation of BaMV in inoculated leaves. Thus, NbRabF1 may be involved in the cell-to-cell movement of BaMV. The potential acyl modification sites at the second and third amino acid positions of NbRabF1 were crucial for membrane targeting and BaMV accumulation. The localization of mutant forms of NbRabF1 with the GDP-bound (donor site) and GTP-bound (acceptor site) suggested that NbRabF1 might regulate vesicle trafficking between the Golgi apparatus and plasma membrane. Furthermore, GTPase activity could also be involved in BaMV cell-to-cell movement. Overall, in this study, we identified a small GTPase, NbRabF1, from N. benthamiana that interacts with its activation protein NbRabGAP1 and regulates vesicle transport from the Golgi apparatus to the plasma membrane. We suggest that the BaMV movement complex might move from cell to cell through this vesicle trafficking route.