Identification and characterization of two novel genomic RNA segments of fig mosaic virus, RNA5 and RNA6.

Fig mosaic virus (FMV), a negative-strand RNA virus, is recognized as a causal agent of fig mosaic disease. We performed RT-PCR for 14 FMV isolates collected from symptomatic fig plants in Japan and Serbia using primers corresponding to the conserved 13 nt stretches found at the termini of FMV genomic segments. The resulting simultaneous amplification of all FMV genomic segments yielded four previously identified segments of FMV and two novel segments. These novel FMV genomic RNA segments were found in each of the 14 FMV isolates analysed. In Northern blot studies, both the sense and antisense strands of these novel RNA molecules accumulated in FMV-infected fig leaves but not in uninfected fig leaves, confirming that they replicate as FMV genomic segments. Sequence analysis showed that the novel RNA segments are similar, in their structural organization and molecular evolutionary patterns, to those of known FMV genomic RNA segments. Our findings thus indicate that these newly discovered RNA segments are previously unidentified FMV genomic segments, which we have designated RNA5 and RNA6.