title: A viral suppressor of RNA silencing differentially regulates the accumulation of short interfering RNAs and micro-RNAs in tobacco.
abstract: Two major classes of small noncoding RNAs have emerged as important regulators of gene expression in eukaryotes, the short interfering RNAs (siRNAs) associated with RNA silencing and endogenous micro-RNAs (miRNAs) implicated in regulation of gene expression. Helper component-proteinase (HC-Pro) is a viral protein that blocks RNA silencing in plants. Here we examine the effect of HC-Pro on the accumulation of siRNAs and endogenous miRNAs. siRNAs were analyzed in transgenic tobacco plants silenced in response to three different classes of transgenes: sense-transgenes, inverted-repeat transgenes, and amplicon-transgenes. HC-Pro suppressed silencing in each line, blocking accumulation of the associated siRNAs and allowing accumulation of transcripts from the previously silenced loci. HC-Pro-suppression of silencing in the inverted-repeat- and amplicon-transgenic lines was accompanied by the apparent accumulation of long double-stranded RNAs and proportional amounts of small RNAs that are larger than the siRNAs that accumulate during silencing. Analysis of these results suggests that HC-Pro interferes with silencing either by inhibiting siRNA processing from double-stranded RNA precursors or by destabilizing siRNAs. In contrast to siRNAs, the accumulation of endogenous miRNAs was greatly enhanced in all of the HC-Pro-expressing lines. Thus, our results demonstrate that accumulation of siRNAs and miRNAs in plants can be differentially regulated by a viral protein. The fact that HC-Pro affects the miRNA pathway raises the possibility that this pathway is targeted by plant viruses as a means to control gene expression in the host.
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia 29208, USA.
authors.forename: Allison C
authors.initials: AC
authors.lastname: Mallory
authors.forename: Brenda J
authors.initials: BJ
authors.lastname: Reinhart
authors.forename: David
authors.initials: D
authors.lastname: Bartel
authors.forename: Vicki B
authors.initials: VB
authors.lastname: Vance
authors.forename: Lewis H
authors.initials: LH
authors.lastname: Bowman
mesh_terms: D005966:Glucuronidase / Q000235:genetics; D030821:Plants, Genetically Modified; D034622:RNA Interference / Q000502:physiology*; D012330:RNA, Double-Stranded / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics*; D014026:Nicotiana / Q000235:genetics* / Q000821:virology
chemical_list: D012330:RNA, Double-Stranded; D018749:RNA, Plant; D034741:RNA, Small Interfering; D005966:Glucuronidase