A cypovirus encoded microRNA negatively regulates the NF-κB pathway to enhance viral multiplication in Silkworm, Bombyx mori

MicroRNAs (miRNAs) are small non-coding RNAs that function as novel gene expression regulators at the post transcriptional level. Not with standing that the biogenesis and function of miRNAs are well-understood in eukaryotes, little is known about RNA virus-encoded miRNAs. Bombyx mori cypovirus (BmCPV) is a double stranded RNA virus with a segmented genome that causes cytoplasmic polyhedrosis disease in silkworm larvae. To date, the interaction between BmCPV and silkworm remains largely unclear. 22 candidate BmCPVencoded miRNAs were identified in this study through small RNA sequencing, stem-loop RT-PCR and qRTPCR. Then, generation and function analyses were conducted on one of the candidate miRNAs, BmCPV-miR-1, in the BmN cells and the silkworm larvae by RNA interference, quantitative PCR, dual-luciferase assay. Our results revealed that BmCPV-miR-1 was encoded by BmCPV genome RNA rather than the degraded fragments of the viral genome. Its generation depended on Dicer-1 and might also be correlated with Dicer-2, Argonaute-1 and Argonaute-2. Moreover, BmCPV-miR-1 could suppress the expression of the target gene, B. mori inhibitor of nuclear factor kappa-B kinase subunit beta (BmIKK beta), via binding to the target mRNA 3 & PRIME;-untranslated region, which fine-tuned the host NF -KB signaling pathway and consequently enhanced viral replication. Our results provide new evidence supporting the hypothesis that RNA viruses could generate miRNAs to modulate antiviral host defense.

Automated summary

This study identified and analyzed miRNAs encoded by BmCPV, a double stranded RNA virus. The results showed that these miRNAs are generated by the viral genome and can modulate the host NF-KB signaling pathway to enhance viral replication.