Bombyx mori cypovirus (BmCPV) is one of the most infectious pathogen in sericulture and a member of the family Reoviridae. It specifically infects the midgut of silkworm. The BmCPV genome consists of 10 dsRNAs segments (S1-S10)， which have generally been assumed to be monocistronic. In this study， a small open reading frame encoding the peptide S5-sORF， containing 27 amino acid residues， was predicted in a region of the negative (-) strand of BmCPV segment S5. An immunofluorescence assay detected S5-sORF in the cytoplasm and nuclei of BmCPV-infected cells， and it was also detected in the virion with western blotting， suggesting that S5-sORF may be assembled into the BmCPV virion. Viral gene expressi... More
Bombyx mori cypovirus (BmCPV) is one of the most infectious pathogen in sericulture and a member of the family Reoviridae. It specifically infects the midgut of silkworm. The BmCPV genome consists of 10 dsRNAs segments (S1-S10)， which have generally been assumed to be monocistronic. In this study， a small open reading frame encoding the peptide S5-sORF， containing 27 amino acid residues， was predicted in a region of the negative (-) strand of BmCPV segment S5. An immunofluorescence assay detected S5-sORF in the cytoplasm and nuclei of BmCPV-infected cells， and it was also detected in the virion with western blotting， suggesting that S5-sORF may be assembled into the BmCPV virion. Viral gene expression was inhibited by overexpressed S5-sORF， and viral multiplication was dose-dependently suppressed by the S5-sORF peptide. A viable recombinant virus， BmCPV-S5-sORF， in which the start codon (ATG) of S5-sORF was mutated to a stop codon (TGA)， was generated with reverse genetics. The proliferation of BmCPV was increased by the abolition of S5-sORF expression. Furthermore， the RNA transcript of S5-sORF and small peptide of S5-sORF were involved in BmCPV replication. The expression of genes related to the innate immune pathways and apoptosis in the silkworm were not significantly affected by S5-sORF overexpression. Our results suggest that a viral nucleotide sequence is utilized by the host to generate an antiviral peptide， which may be a novel strategy protecting the host from viral infection.
