Caenorhabditis elegansRIG-I Homolog Mediates Antiviral RNA Interference Downstream of Dicer-Dependent Biogenesis of Viral Small Interfering RNAs.
Dicer enzymes process virus-specific double-stranded RNA (dsRNA) into small interfering RNAs (siRNAs) to initiate specific antiviral defense by related RNA interference (RNAi) pathways in plants, insects, nematodes, and mammals. Antiviral RNAi inCaenorhabditis elegansrequires Dicer-related helicase 1 (DRH-1), not found in plants and insects but highly homologous to mammalian retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), intracellular viral RNA sensors that trigger innate immunity against RNA virus infection. However, it remains unclear if DRH-1 acts analogously to initiate antiviral RNAi inC. elegansHere, we performed a forward genetic screen to characterize antiviral RNAi inC. elegansUsing a mapping-by-sequencing strategy, we uncovered four loss-of-function alleles ofdrh-1, three of which caused mutations in the helicase and C-terminal domains conserved in RLRs. Deep sequencing of small RNAs revealed an abundant population of Dicer-dependent virus-derived small interfering RNAs (vsiRNAs) indrh-1single and double mutant animals after infection with Orsay virus, a positive-strand RNA virus. These findings provide further genetic evidence for the antiviral function of DRH-1 and illustrate that DRH-1 is not essential for the sensing and Dicer-mediated processing of the viral dsRNA replicative intermediates. Interestingly, vsiRNAs produced bydrh-1mutants were mapped overwhelmingly to the terminal regions of the viral genomic RNAs, in contrast to random distribution of vsiRNA hot spots when DRH-1 is functional. As RIG-I translocates on long dsRNA and DRH-1 exists in a complex with Dicer, we propose that DRH-1 facilitates the biogenesis of vsiRNAs in nematodes by catalyzing translocation of the Dicer complex on the viral long dsRNA precursors.IMPORTANCEThe helicase and C-terminal domains of mammalian RLRs sense intracellular viral RNAs to initiate the interferon-regulated innate immunity against RNA virus infection. Both of the domains from human RIG-I can substitute for the corresponding domains of DRH-1 to mediate antiviral RNAi inC. elegans, suggesting an analogous role for DRH-1 as an intracellular dsRNA sensor to initiate antiviral RNAi. Here, we developed a forward genetic screen for the identification of host factors required for antiviral RNAi inC. elegansCharacterization of four distinctdrh-1mutants obtained from the screen revealed that DRH-1 did not function to initiate antiviral RNAi. We show that DRH-1 acted in a downstream step to enhance Dicer-dependent biogenesis of viral siRNAs inC. elegansAs mammals produce Dicer-dependent viral siRNAs to target RNA viruses, our findings suggest a possible role for mammalian RLRs and interferon signaling in the biogenesis of viral siRNAs.
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.|Graduate Program in Genetics, Genomics and Bioinformatics, University of California, Riverside, California, USA.
Stephanie R
SR
Coffman
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.
Jinfeng
J
Lu
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.
Xunyang
X
Guo
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.
Jing
J
Zhong
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.
Hongshan
0000-0002-9605-2467
H
Jiang
Biology Department, University of California, Riverside, California, USA.
Gina
G
Broitman-Maduro
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA.
Wan-Xiang
WX
Li
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana, USA.
Rui
R
Lu
Biology Department, University of California, Riverside, California, USA.
Morris
M
Maduro
Department of Plant Pathology and Microbiology, University of California, Riverside, California, USA shou-wei.ding@ucr.edu.|Graduate Program in Genetics, Genomics and Bioinformatics, University of California, Riverside, California, USA.
Shou-Wei
SW
Ding
D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000276:immunology*; D029742:Caenorhabditis elegans Proteins / Q000378:metabolism*; D053487:DEAD-box RNA Helicases / Q000378:metabolism*; D005820:Genetic Testing; D034622:RNA Interference; D012328:RNA Viruses / Q000276:immunology*; D034741:RNA, Small Interfering / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D034741:RNA, Small Interfering; C461646:DRH-1 protein, C elegans; D053487:DEAD-box RNA Helicases
Caenorhabditis elegans; DRH-1; RNA interference; antiviral defense