The genome segment S5 of rice black-streaked dwarf virus (genus Fijivirus, family Reoviridae) is functionally bicistronic in infected plants. It has a conserved second ORF (P5-2) partially overlapping the major ORF in a different reading frame, but its function remains unknown. P5-2 was detected in infected plants, but not in purified viral particles by Western blotting, indicating that it is a non-structural protein. In immunoelectron microscopy, polyclonal antibodies against P5-2 specifically labelled chloroplasts of infected rice plants. When P5-2 fused with green fluorescent protein was transiently expressed in leaves of Nicotiana benthamiana, fluorescence was also co-localized with chloroplasts. Experiments with deletion mutants of P5-2 showed that its N-terminal part was responsible for its targeting to chloroplasts.
