title: Satellite RNAs interfere with the function of viral RNA silencing suppressors.
abstract: Viral satellite RNAs (satRNAs) are small subviral RNAs and depend on the helper virus for replication and spread. satRNAs can attenuate helper virus-induced symptoms, the mechanism of which remains unclear. Here, we show that two virus-encoded suppressors of RNA silencing (VSRs), Cucumber mosaic virus (CMV) 2b and Tombusvirus P19, suppress hairpin RNA (hpRNA)-induced silencing of a β-glucuronidase (GUS) gene in Nicotiana benthamiana. This suppression can be overcome by CMV Y-satellite RNA (Y-Sat) via the Y-Sat-derived small interfering RNAs (siRNAs), which bind to the VSRs and displace the bound hpGUS-derived siRNAs. We also show that microRNA target gene expression in N. tabacum was elevated by CMV infection, presumably due to function of the 2b VSR, but this upregulation of microRNA target genes was reversed in the presence of Y-Sat. These results suggest that satRNA infection minimizes the effect of VSRs on host siRNA and microRNA-directed silencing. Our results suggest that the high abundance of satRNA-derived siRNAs contributes to symptom attenuation by binding helper virus-encoded VSRs, minimizing the capacity of the VSRs to bind host siRNA and miRNA and interfere with their function.
authors.affiliation: National Citrus Engineering Research Center, Citrus Research Institute, Southwest University Chongqing, China ; Commonwealth Scientific and Industrial Research Organisation Plant Industry Canberra, ACT, Australia.
authors.forename: Wan-Xia
authors.initials: WX
authors.lastname: Shen
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Plant Industry Canberra, ACT, Australia.
authors.forename: Phil Chi Khang
authors.initials: PC
authors.lastname: Au
authors.affiliation: Department of Plant Science, Waite Institute, Adelaide University Glen Osmond, SA, Australia.
authors.forename: Bu-Jun
authors.initials: BJ
authors.lastname: Shi
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Plant Industry Canberra, ACT, Australia.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Smith
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Plant Industry Canberra, ACT, Australia.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Dennis
authors.affiliation: State Key Laboratory of Plant Genomics, Institute of Microbiology, Chinese Academy of Sciences Beijing, China.
authors.forename: Hui-Shan
authors.initials: HS
authors.lastname: Guo
authors.affiliation: National Citrus Engineering Research Center, Citrus Research Institute, Southwest University Chongqing, China.
authors.forename: Chang-Yong
authors.initials: CY
authors.lastname: Zhou
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation Plant Industry Canberra, ACT, Australia.
authors.forename: Ming-Bo
authors.initials: MB
authors.lastname: Wang
keywords: RNA silencing; microRNA expression; satellite RNA; symptom attenuation; virus-encoded suppressor