Functional analysis of antisense long non-coding RNAs transcribed from the Bombyx mori (Lepidoptera: Bombycidae) nucleopolyhedrovirus genome

Although some viruses have been shown to encode long non-coding RNAs (lncRNAs), how they function during their infection cycles remains elusive. We previously found an unexpectedly large number of novel transcripts, including putative lncRNAs, which were expressed from the genome of the baculovirus Bombyx mori nucleopolyhedrovirus (BmNPV). To investigate the function of baculoviral antisense lncRNAs, we selected 15 BmNPV lncRNAs expressed from the baculovirus early or late promoter motif, and constructed the corresponding promoter knockout (PKO) viruses in which nucleotide substitutions were introduced at the transcription start sites of lncRNAs. We investigated the production of budded viruses (BVs) and occlusion bodies (OBs) in PKO virus-infected cultured cells and silkworm larvae. No defects in BV and OB production were observed for most of the PKO viruses, whereas KO122AS, in which an antisense lncRNA in the Bm122 locus was disrupted, produced fewer OBs than the wild-type or repair virus both in cultured cells and in silkworm larvae. Northern blot analysis revealed that loss of this antisense lncRNAs reduced the amounts of the corresponding sense mRNA. These results suggest that the lncRNA transcribed from the Bm122 locus might contribute to virus propagation by regulating viral gene expression. This is the first study to characterize the properties and functions of baculoviral lncRNAs.