Abstract
RNA interference (RNAi), especially the small interfering RNA (siRNA) and microRNA (miRNA) pathways, plays an important role in defending against viruses in plants and insects. However, how insect-transmitted phytoviruses regulate the RNAi-mediated antiviral response in vector insects has barely been uncovered. In this study, we explored the interaction between rice stripe virus (RSV) and the miRNA and siRNA pathways of the small brown planthopper, which is a vector insect. The transcript and protein levels of key genes in the two RNAi pathways did not change during the RSV infection process. When the expression of insect Ago1, Ago2, or Translin was silenced by the injection of double-stranded RNAs targeting these genes, viral replication was promoted with Ago2 silencing but inhibited with Translin silencing. Protein-protein binding assays showed that viral NS2 and RNA-dependent RNA polymerase interacted with insect Ago2 and Translin, respectively. When NS2 was knocked down, the transcript level of Ago2 increased and viral replication was inhibited. Therefore, viral NS2 behaved like an siRNA suppressor in vector insects. This protein-binding regulation of insect RNAi systems reflects a complicated and diverse coevolution of viruses with their vector insects.
Highlights
RNA interference (RNAi) is a sequence-specific gene silencing phenomenon in eukaryotes and is usually induced by small RNA molecules, including small interfering RNAs, microRNAs, and piwi-interacting RNAs [1,2]
To determine if rice stripe virus (RSV) infection led to transcriptomic changes in 8 key genes of the miRNA and small interfering RNA (siRNA) pathways, infected planthoppers were used to measure transcript levels via quantitative real-time PCR
RSV crude preparations from viruliferous planthoppers were injected into nonviruliferous planthoppers, viral replication was observed from 6 d after injection (DAI) as shown by an increase in nucleocapsid protein (NP) RNA levels (Figure 1A, F(4, 35) = 43.5, p < 0.0001)
Summary
RNA interference (RNAi) is a sequence-specific gene silencing phenomenon in eukaryotes and is usually induced by small RNA molecules, including small interfering RNAs (siRNAs), microRNAs (miRNAs), and piwi-interacting RNAs (piRNAs) [1,2]. RNAi plays an important role in natural defense against viruses, which act as initiators and as targets of gene silencing, especially in plants and insects [3,4]. The siRNA pathway is activated to target viral genomes for direct degradation or to target host genes for the regulation of viral replication [4,5]. MiRNAs are produced to regulate the expression of host genes or viral genes through miRNA-viral RNA interactions that affect viral replication [6,7]. Several studies exist regarding the RNAi-mediated anti-viral responses against phytoviruses in plants [3,8,9,10,11,12]. The interactions between insect-transmitted phytoviruses and the RNAi pathways of vector insects remain elusive
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