scholarly journals Antiviral Defense Involves AGO4 in an Arabidopsis–Potexvirus Interaction

2016 ◽  
Vol 29 (11) ◽  
pp. 878-888 ◽  
Author(s):  
Chantal Brosseau ◽  
Mohamed El Oirdi ◽  
Ayooluwa Adurogbangba ◽  
Xiaofang Ma ◽  
Peter Moffett
Keyword(s):  
Gene Expression ◽  
Nuclear Localization ◽  
Rna Silencing ◽  
Defense Mechanism ◽  
Rna Viruses ◽  
Antiviral Defense ◽  
Double Stranded Rna ◽  
Micro Rnas ◽  
Plantago Asiatica ◽  
Antiviral Activities

In plants, RNA silencing regulates gene expression through the action of Dicer-like (DCL) and Argonaute (AGO) proteins via micro RNAs and RNA-dependent DNA methylation (RdDM). In addition, RNA silencing functions as an antiviral defense mechanism by targeting virus-derived double-stranded RNA. Plants encode multiple AGO proteins with specialized functions, including AGO4-like proteins that affect RdDM and AGO2, AGO5, and AGO1, which have antiviral activities. Here, we show that AGO4 is also required for defense against the potexvirus Plantago asiatica mosaic virus (PlAMV), most likely independent of RdDM components such as DCL3, Pol IV, and Pol V. Transient assays showed that AGO4 has direct antiviral activity on PlAMV and, unlike RdDM, this activity does not require nuclear localization of AGO4. Furthermore, although PlAMV infection causes a decrease in AGO4 expression, PlAMV causes a change in AGO4 localization from a largely nuclear to a largely cytoplasmic distribution. These results indicate an important role for AGO4 in targeting plant RNA viruses as well as demonstrating novel mechanisms of regulation of and by AGO4, independent of its canonical role in regulating gene expression by RdDM.

scholarly journals The Suppressor of Transgene RNA Silencing Encoded by Cucumber mosaic virus Interferes with Salicylic Acid-Mediated Virus Resistance

2001 ◽  
Vol 14 (6) ◽  
pp. 715-724 ◽  
Author(s):  
Liang-Hui Ji ◽  
Shou-Wei Ding
Keyword(s):  
Salicylic Acid ◽  
Cucumber Mosaic Virus ◽  
Mosaic Virus ◽  
Virus Resistance ◽  
Rna Silencing ◽  
Defense Mechanism ◽  
Antiviral Defense ◽  
Oxidase Gene ◽  
Systemic Spread ◽  
Systemic Infections

The Cucumber mosaic virus (CMV)-encoded 2b protein (Cmv2b) is a nuclear protein that suppresses transgene RNA silencing in Nicotiana benthamiana. Cmv2b is an important virulence determinant but nonessential for systemic spread in N. glutinosa, in contrast to its indispensable role for systemic infections in cucumber. Here, we report that Cmv2b became essential for systemic infections in older N. glutinosa plants or in young seedlings pre-treated with salicylic acid (SA). Expression of Cmv2b from the genome of either CMV or Tobacco mosaic virus significantly reduced the inhibitory effect of SA on virus accumulation in inoculated leaves and systemic leaves. A close correlation is demonstrated between Cmv2b expression and a reduced SA-dependent induction of the alternative oxidase gene, a component of the recently proposed SA-regulated antiviral defense. These results collectively reveal a novel activity of Cmv2b in the inhibition of SA-mediated virus resistance. We used a N. tabacum line expressing a bacterial nahG transgene that degrades SA to provide evidence for a Cmv2b-sensitive antiviral defense mechanism in tobacco in which SA acts as a positive modifier but not as an essential component. We propose that SA induces virus resistance by potentiating a RNA-silencing antiviral defense that is targeted by Cmv2b.

scholarly journals Computational analysis of microRNA-mediated interactions in SARS-CoV-2 infection

2020 ◽  
Author(s):  
Müşerref Duygu Saçar Demirci ◽  
Aysun Adan
Keyword(s):  
Gene Expression ◽  
Computational Analysis ◽  
Defense Mechanism ◽  
Function Analysis ◽  
Antiviral Defense ◽  
Cellular Processes ◽  
Human Mirnas ◽  
Human Genes ◽  
Viral Genes ◽  
Gene Function Analysis

AbstractMicroRNAs (miRNAs) are post-transcriptional regulators of gene expression that have been found in more than 200 diverse organisms. Although it is still not fully established if RNA viruses could generate miRNAs that would target their own genes or alter the host gene expression, there are examples of miRNAs functioning as an antiviral defense mechanism. In the case of Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), there are several mechanisms that would make miRNAs impact the virus, like interfering with replication, translation and even modulating the host expression. In this study, we performed a machine learning based miRNA prediction analysis for the SARS-CoV-2 genome to identify miRNA-like hairpins and searched for potential miRNA – based interactions between the viral miRNAs and human genes and human miRNAs and viral genes. Our PANTHER gene function analysis results indicate that viral derived miRNA candidates could target various human genes involved in crucial cellular processes including transcription. For instance, a transcriptional regulator, STAT1 and transcription machinery might be targeted by virus-derived miRNAs. In addition, many known human miRNAs appear to be able to target viral genes. Considering the fact that miRNA-based therapies have been successful before, comprehending mode of actions of miRNAs and their possible roles during SARS-CoV-2 infections could create new opportunities for the development and improvement of new therapeutics.

scholarly journals Homologous recombination is an intrinsic defense against antiviral RNA interference

2018 ◽  
Vol 115 (39) ◽  
pp. E9211-E9219 ◽  
Author(s):  
Lauren C. Aguado ◽  
Tristan X. Jordan ◽  
Emily Hsieh ◽  
Daniel Blanco-Melo ◽  
John Heard ◽  
...  
Keyword(s):  
Rna Interference ◽  
Homologous Recombination ◽  
Virus Replication ◽  
Defense Mechanism ◽  
Selective Pressure ◽  
Rna Viruses ◽  
Antiviral Defense ◽  
Dynamic Relationship ◽  
Pathogen Prevalence ◽  
Genomic Material

RNA interference (RNAi) is the major antiviral defense mechanism of plants and invertebrates, rendering the capacity to evade it a defining factor in shaping the viral landscape. Here we sought to determine whether different virus replication strategies provided any inherent capacity to evade RNAi in the absence of an antagonist. Through the exploitation of host microRNAs, we recreated an RNAi-like environment in vertebrates and directly compared the capacity of positive- and negative-stranded RNA viruses to cope with this selective pressure. Applying this defense against four distinct viral families revealed that the capacity to undergo homologous recombination was the defining attribute that enabled evasion of this defense. Independent of gene expression strategy, positive-stranded RNA viruses that could undergo strand switching rapidly excised genomic material, while negative-stranded viruses were effectively targeted and cleared upon RNAi-based selection. These data suggest a dynamic relationship between host antiviral defenses and the biology of virus replication in shaping pathogen prevalence.

scholarly journals Multiple Functions of Rice Dwarf Phytoreovirus Pns10 in Suppressing Systemic RNA Silencing

2010 ◽  
Vol 84 (24) ◽  
pp. 12914-12923 ◽  
Author(s):  
Bo Ren ◽  
Yuanyuan Guo ◽  
Feng Gao ◽  
Peng Zhou ◽  
Feng Wu ◽  
...  
Keyword(s):  
Nicotiana Benthamiana ◽  
Rna Silencing ◽  
Rna Stability ◽  
Antiviral Defense ◽  
Double Stranded Rna ◽  
Systemic Spread ◽  
Dsrna Viruses ◽  
Systemic Rna ◽  
Interfering Rna ◽  
Diverse Groups

ABSTRACT RNA silencing is a potent mechanism of antiviral defense response in plants and other organisms. For counterdefense, viruses have evolved a variety of suppressors of RNA silencing (VSRs) that can inhibit distinct steps of a silencing pathway. We previously identified Pns10 encoded by Rice dwarf phytoreovirus (RDV) as a VSR, the first of its kind from double-stranded RNA (dsRNA) viruses. In this study we investigated the mechanisms of Pns10 function in suppressing systemic RNA silencing in the widely used Nicotiana benthamiana model plant. We report that Pns10 suppresses local and systemic RNA silencing triggered by sense mRNA, enhances viral replication and/or viral RNA stability in inoculated leaves, accelerates the systemic spread of viral infection, and enables viral invasion of shoot apices. Mechanistically, Pns10 interferes with the perception of silencing signals in recipient tissues, binds double-stranded small interfering RNA (siRNAs) with two-nucleotide 3′ overhangs, and causes the downregulated expression of RDR6. These results significantly deepen our mechanistic understanding of the VSR functions encoded by a dsRNA virus and contribute additional evidence that binding siRNAs and interfering with RDR6 expression are broad mechanisms of VSR functions encoded by diverse groups of viruses.

scholarly journals Differential Inductions of RNA Silencing among Encapsidated Double-Stranded RNA Mycoviruses in the White Root Rot Fungus Rosellinia necatrix

2016 ◽  
Vol 90 (12) ◽  
pp. 5677-5692 ◽  
Author(s):  
Hajime Yaegashi ◽  
Takeo Shimizu ◽  
Tsutae Ito ◽  
Satoko Kanematsu
Keyword(s):  
Rna Silencing ◽  
Defense Mechanism ◽  
Fluorescent Protein ◽  
Constitutive Expression ◽  
Phytopathogenic Fungus ◽  
Rosellinia Necatrix ◽  
Double Stranded Rna ◽  
Content Type ◽  
Molecular Features ◽  
Fungal Viruses

ABSTRACTRNA silencing acts as a defense mechanism against virus infection in a wide variety of organisms. Here, we investigated inductions of RNA silencing against encapsidated double-stranded RNA (dsRNA) fungal viruses (mycoviruses), including a partitivirus (RnPV1), a quadrivirus (RnQV1), a victorivirus (RnVV1), a mycoreovirus (RnMyRV3), and a megabirnavirus (RnMBV1) in the phytopathogenic fungusRosellinia necatrix. Expression profiling of RNA silencing-related genes revealed that a dicer-like gene, an Argonaute-like gene, and two RNA-dependent RNA polymerase genes were upregulated by RnMyRV3 or RnMBV1 infection but not by other virus infections or by constitutive expression of dsRNA inR. necatrix. Massive analysis of viral small RNAs (vsRNAs) from the five mycoviruses showed that 19- to 22-nucleotide (nt) vsRNAs were predominant; however, their ability to form duplexes with 3′ overhangs and the 5′ nucleotide preferences of vsRNAs differed among the five mycoviruses. The abundances of 19- to 22-nt vsRNAs from RnPV1, RnQV1, RnVV1, RnMyRV3, and RnMBV1 were 6.8%, 1.2%, 0.3%, 13.0%, and 24.9%, respectively. Importantly, the vsRNA abundances and accumulation levels of viral RNA were not always correlated, and the origins of the vsRNAs were distinguishable among the five mycoviruses. These data corroborated diverse interactions between encapsidated dsRNA mycoviruses and RNA silencing. Moreover, a green fluorescent protein (GFP)-based sensor assay inR. necatrixrevealed that RnMBV1 infection induced silencing of the target sensor gene (GFP gene and the partial RnMBV1 sequence), suggesting that vsRNAs from RnMBV1 activated the RNA-induced silencing complex. Overall, this study provides insights into RNA silencing against encapsidated dsRNA mycoviruses.IMPORTANCEEncapsidated dsRNA fungal viruses (mycoviruses) are believed to replicate inside their virions; therefore, there is a question of whether they induce RNA silencing. Here, we investigated inductions of RNA silencing against encapsidated dsRNA mycoviruses (a partitivirus, a quadrivirus, a victorivirus, a mycoreovirus, and a megabirnavirus) inRosellinia necatrix. We revealed upregulation of RNA silencing-related genes inR. necatrixinfected with a mycoreovirus or a megabirnavirus but not with other viruses, which was consistent with the relatively high abundances of vsRNAs from the two mycoviruses. We also showed common and different molecular features and origins of the vsRNAs from the five mycoviruses. Furthermore, we demonstrated the activation of RNA-induced silencing complex by mycoviruses inR. necatrix. Taken together, our data provide insights into an RNA silencing pathway against encapsidated dsRNA mycoviruses which is differentially induced among encapsidated dsRNA mycoviruses; that is, diverse replication strategies exist among encapsidated dsRNA mycoviruses.

scholarly journals Evidence that RNA silencing functions as an antiviral defense mechanism in fungi

2007 ◽  
Vol 104 (31) ◽  
pp. 12902-12906 ◽  
Author(s):  
G. C. Segers ◽  
X. Zhang ◽  
F. Deng ◽  
Q. Sun ◽  
D. L. Nuss
Keyword(s):  
Rna Silencing ◽  
Defense Mechanism ◽  
Antiviral Defense

scholarly journals Viral Class 1 RNase III Involved in Suppression of RNA Silencing

2005 ◽  
Vol 79 (11) ◽  
pp. 7227-7238 ◽  
Author(s):  
Jan F. Kreuze ◽  
Eugene I. Savenkov ◽  
Wilmer Cuellar ◽  
Xiangdong Li ◽  
Jari P. T. Valkonen
Keyword(s):  
Nicotiana Benthamiana ◽  
Rna Silencing ◽  
Rna Virus ◽  
Antiviral Defense ◽  
Rnase Iii ◽  
Double Stranded Rna ◽  
Class 1 ◽  
Heterologous Virus ◽  
Silencing Suppression ◽  
Interfering Rna

ABSTRACT Double-stranded RNA (dsRNA)-specific endonucleases belonging to RNase III classes 3 and 2 process dsRNA precursors to small interfering RNA (siRNA) or microRNA, respectively, thereby initiating and amplifying RNA silencing-based antiviral defense and gene regulation in eukaryotic cells. However, we now provide evidence that a class 1 RNase III is involved in suppression of RNA silencing. The single-stranded RNA genome of sweet potato chlorotic stunt virus (SPCSV) encodes an RNase III (RNase3) homologous to putative class 1 RNase IIIs of unknown function in rice and Arabidopsis. We show that RNase3 has dsRNA-specific endonuclease activity that enhances the RNA-silencing suppression activity of another protein (p22) encoded by SPCSV. RNase3 and p22 coexpression reduced siRNA accumulation more efficiently than p22 alone in Nicotiana benthamiana leaves expressing a strong silencing inducer (i.e., dsRNA). RNase3 did not cause intracellular silencing suppression or reduce accumulation of siRNA in the absence of p22 or enhance silencing suppression activity of a protein encoded by a heterologous virus. No other known RNA virus encodes an RNase III or uses two independent proteins cooperatively for RNA silencing suppression.

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