Abstract
Circular DNAs derived from single-stranded RNA viruses play important roles in counteracting viral infection. However, whether double-stranded RNA viruses generate functional circular DNAs is still unknown. Using circDNA sequencing, divergent PCR, DNA in situ hybridization and rolling circular amplification, we presently confirmed that in silkworm, Bombyx mori cytoplasmic polyhedrosis virus (BmCPV), a double-stranded RNA virus belonging to cypovirus, is prone to produce a BmCPV-derived circular DNA termed as vcDNA-S7. We have also found that vcDNA-S7 formation is mediated by endogenous reverse transcriptase (RT), and the proliferation of BmCPV can be inhibited by vcDNA-S7 in vitro and in vivo. Moreover, we have discovered that the silkworm RNAi immune pathway is activated by vcDNA-S7, while viral small interfering RNAs (vsiRNAs) derived from transcribed RNA by vcDNA-S7 can be detected by small RNA deep sequencing. These results suggest that BmCPV-derived vcDNA-S7, mediated by RT, can serve as a template for the biogenesis of antiviral siRNAs, which may lead to the repression of BmCPV infection. To our knowledge, this is the first demonstration that a circular DNA, produced by double stranded RNA viruses, is capable of regulating virus infection.
Highlights
Some studies have shown that certain single-stranded RNA viruses can produce viral circular DNAs, mediated by the host retrotransposon, which have an important role in controlling virus infection [8, 9]
Bombyx mori cytoplasmic polyhedrosis virus (BmCPV)-Derived vcDNA-S7 Is Present in BmCPV-Infected Cells circDNAs ubiquitous forms of DNA that are generally found in DNA viruses, bacteria, as well as the mitochondria and chloroplasts of eukaryotes
To explore whether BmCPV infection could affect the generation of extrachromosomal circular DNAs (eccDNAs) in B. mori, we performed circDNA sequencing of midgut from B. mori infected with BmCPV
Summary
Due to its limited genome size and more restricted number of genes, viruses typically depend on host cells to achieve its proper infection and proliferation. Some studies have shown that certain single-stranded RNA viruses can produce viral circular DNAs (vcircDNAs), mediated by the host retrotransposon, which have an important role in controlling virus infection [8, 9]. The genomic RNA of a number of viruses, such as Drosophila C virus (DCV), flow house virus (FHV), Sindbis virus (SNV), and chikungunya virus (CHIKV), can form stable and chimeric vcircDNAs, mediated by retrotransposons. These vcircDNAs have transcriptional ability and can stably (and continuously) transcribe RNAs to produce a higher abundance of vsiRNAs, leading to a persistence of the viral infection by RNAi pathways [8, 9]. It is not yet known whether double stranded RNA viruses can form vcircDNAs during viral infection
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