The 1b gene of raspberry bushy dwarf virus is a virulence component that facilitates systemic virus infection in plants.

A product translated from the 1b gene of raspberry bushy dwarf virus (RBDV) was specifically detected in RBDV-infected Nicotiana benthamiana plants by immunoblot analysis. To analyze the effects of the 1b gene on virus infection in host plants, an RBDV deletion mutant virus (RB∆1bstop), which is unable to express the 1b gene, was constructed and inoculated to N. benthamiana plants. The results showed that accumulation of the virus genomic (g) RNAs 1 and 2 decreased in inoculated leaves, and that systemic virus spread was delayed compared with wild-type RBDV. In contrast, accumulation of the viral gRNAs 1 and 2 was elevated in RB∆1bstop-infected leaf tissues during ectopic expression of the 1b gene. Furthermore, we found that the 1b has weak RNA silencing suppressor activity.