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Ma X, Nicole MC, Meteignier LV, Hong N, Wang G, Moffett P. Different roles for RNA silencing and RNA processing components in virus recovery and virus-induced gene silencing in plants. JOURNAL OF EXPERIMENTAL BOTANY 2015; 66:919-32. [PMID: 25385769 DOI: 10.1093/jxb/eru447] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
A major antiviral mechanism in plants is mediated by RNA silencing, which relies on the cleavage of viral dsRNA into virus-derived small interfering RNAs (vsiRNAs) by DICER-like enzymes. Members of the Argonaute (AGO) family of endonucleases then use these vsiRNA as guides to target viral RNA. This can result in a phenomenon known as recovery, whereby the plant silences viral gene expression and recovers from viral symptoms. Endogenous mRNAs can also be targeted by vsiRNAs in a phenomenon known as virus-induced gene silencing (VIGS). Although related to other RNA silencing mechanisms, it has not been established if recovery and VIGS are mediated by the same molecular mechanisms. We used tobacco rattle virus (TRV) carrying a fragment of the phytoene desaturase (PDS) gene (TRV-PDS) or expressing green fluorescent protein (TRV-GFP) as readouts for VIGS and recovery, respectively, in Arabidopsis ago mutants. Our results demonstrated roles for AGO2 and AGO4 in susceptibility to TRV, whereas VIGS of endogenous genes appeared to be largely mediated by AGO1. However, recovery appeared to be mediated by different components, as all the aforementioned mutants were able to recover from TRV-GFP inoculation. TRV RNAs from recovered plants associated less with ribosomes, suggesting that recovery involves translational repression of viral transcripts. Translationally repressed RNAs often accumulate in RNA processing bodies (PBs), where they are eventually processed by decapping enzymes. Consistent with this, we found that viral recovery induced increased PB formation and that a decapping mutant (DCP2) showed increased VIGS and virus RNA accumulation, indicating an important role for PBs in eliminating viral RNA.
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Affiliation(s)
- Xiaofang Ma
- State Key Laboratory of Agricultural Microbiology, Wuhan, Hubei 430070, PR China College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, PR China Université de Sherbrooke, Département de Biologie, 2500 Boulevard de l'Université, Sherbrooke J1K 2R1, QC, Canada
| | - Marie-Claude Nicole
- Université de Sherbrooke, Département de Biologie, 2500 Boulevard de l'Université, Sherbrooke J1K 2R1, QC, Canada
| | - Louis-Valentin Meteignier
- Université de Sherbrooke, Département de Biologie, 2500 Boulevard de l'Université, Sherbrooke J1K 2R1, QC, Canada
| | - Ni Hong
- State Key Laboratory of Agricultural Microbiology, Wuhan, Hubei 430070, PR China College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, PR China
| | - Guoping Wang
- State Key Laboratory of Agricultural Microbiology, Wuhan, Hubei 430070, PR China College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, PR China
| | - Peter Moffett
- Université de Sherbrooke, Département de Biologie, 2500 Boulevard de l'Université, Sherbrooke J1K 2R1, QC, Canada
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52
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Mochizuki T, Ohki ST. Detection of plant virus in meristem by immunohistochemistry and in situ hybridization. Methods Mol Biol 2015; 1236:275-87. [PMID: 25287510 DOI: 10.1007/978-1-4939-1743-3_20] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Most plant viruses do not infect the shoot apical meristem (SAM) of a host plant, and this virus-free region of meristem tissue has been used to obtain virus-free clones by meristem tip culture. Thus, the validation of viral distribution in meristem tissues is important for ensuring the appropriate excision of virus-free meristem tips. Although immunohistochemical microscopy and in situ hybridization are classical techniques, they allow us to determine the presence or absence of plant viruses in the shoot meristem tissues of a host plant. Briefly, meristem tissues are excised from infected plants, fixed, embedded in paraffin medium, and prepared in semithin sections (10-15 μm). By treating these sections with an antibody against viral protein or with a probe complementary to viral RNA, the viral distribution in the meristem tissue can be clearly observed. Importantly, these procedures are broadly applicable to most virus (and viroid) and host plant combinations.
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Affiliation(s)
- Tomofumi Mochizuki
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka, 599-8531, Japan,
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Lukhovitskaya NI, Vetukuri RR, Sama I, Thaduri S, Solovyev AG, Savenkov EI. A viral transcription factor exhibits antiviral RNA silencing suppression activity independent of its nuclear localization. J Gen Virol 2014; 95:2831-2837. [PMID: 25143075 DOI: 10.1099/vir.0.067884-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Viral suppressors of RNA silencing (VSRs) are critical for the success of virus infection and efficient accumulation of virus progeny. The chrysanthemum virus B p12 protein acts as a transcription factor to regulate cell size and proliferation favourable for virus infection. Here, we showed that the p12 protein suppressed RNA silencing and was able to complement a VSR-deficient unrelated virus. Moreover, p12 counter-silencing activity could be uncoupled from its function as a transcription factor in the nucleus. The altered p12 protein, which lacked a nuclear localization signal and was not imported into the nucleus, was able to suppress RNA silencing as efficiently as the native protein. The data revealed new aspects of p12 functioning and identified a novel role for this viral zinc-finger transcription factor. The results provided a general insight into one of the activities of the p12 protein, which appeared to possess more than one function.
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Affiliation(s)
- Nina I Lukhovitskaya
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Box 7080, 75007 Uppsala, Sweden
| | - Ramesh R Vetukuri
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Box 7080, 75007 Uppsala, Sweden
| | - Indu Sama
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Box 7080, 75007 Uppsala, Sweden
| | - Srinivas Thaduri
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Box 7080, 75007 Uppsala, Sweden
| | - Andrey G Solovyev
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119992 Moscow, Russia
| | - Eugene I Savenkov
- Department of Plant Biology, Uppsala BioCenter, Swedish University of Agricultural Sciences, Linnean Center for Plant Biology, Box 7080, 75007 Uppsala, Sweden
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54
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How does the genome structure and lifestyle of a virus affect its population variation? Curr Opin Virol 2014; 9:39-44. [DOI: 10.1016/j.coviro.2014.09.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Revised: 09/02/2014] [Accepted: 09/03/2014] [Indexed: 11/20/2022]
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Atsumi G, Tomita R, Yamashita T, Sekine KT. A novel virus transmitted through pollination causes ring-spot disease on gentian (Gentiana triflora) ovaries. J Gen Virol 2014; 96:431-439. [PMID: 25351517 DOI: 10.1099/vir.0.071498-0] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this study, we identified a novel virus from gentian (Gentiana triflora) that causes ring-spots on ovaries. Furthermore, the virus causes unusual symptoms, ring-spots that appear specifically on the outer surface of the ovarian wall after pollination. Pollen grains carrying the virus were used to infect host plants by hand-pollination. RNA extracted from purified virions indicated that the virus had two segments, RNA1 and RNA2. The full-length cDNA sequence indicated that RNA1 had two ORFs: ORF1 had methyltransferase and helicase motifs, and ORF2 had an RNA-dependent RNA polymerase motif. RNA2 had five ORFs encoding a coat protein, triple gene block proteins 1-3 and a cysteine-rich protein. The length of RNA1 was 5519 bases and that of RNA2 was 3810 bases not including a polyU/polyA region between the first and second ORFs. Viral RNA does not have a polyA tail at the 3' end. Sequence similarity and phylogenetic analysis suggested that the virus is closely related to members of the genera Pecluvirus and Hordeivirus but distinct from them. These combined results suggest that the causal agent inducing ring-spot symptoms on gentian ovaries is a new virus belonging to the family Virgaviridae but not to any presently known genus. We tentatively name the virus gentian ovary ring-spot virus.
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Affiliation(s)
- Go Atsumi
- Iwate Biotechnology Research Center, Kitakami 024-0003, Iwate, Japan
| | - Reiko Tomita
- Iwate Biotechnology Research Center, Kitakami 024-0003, Iwate, Japan
| | | | - Ken-Taro Sekine
- Iwate Biotechnology Research Center, Kitakami 024-0003, Iwate, Japan
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56
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Baulcombe DC, Dean C. Epigenetic regulation in plant responses to the environment. Cold Spring Harb Perspect Biol 2014; 6:a019471. [PMID: 25183832 DOI: 10.1101/cshperspect.a019471] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In this article, we review environmentally mediated epigenetic regulation in plants using two case histories. One of these, vernalization, mediates adaptation of plants to different environments and it exemplifies processes that are reset in each generation. The other, virus-induced silencing, involves transgenerationally inherited epigenetic modifications. Heritable epigenetic marks may result in heritable phenotypic variation, influencing fitness, and so be subject to natural selection. However, unlike genetic inheritance, the epigenetic modifications show instability and are influenced by the environment. These two case histories are then compared with other phenomena in plant biology that are likely to represent epigenetic regulation in response to the environment.
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Affiliation(s)
- David C Baulcombe
- Department of Plant Science, University of Cambridge, Cambridge CB2 3EA, United Kingdom
| | - Caroline Dean
- Department of Cell and Developmental Biology, John Innes Centre, Norwich NR4 7UH, United Kingdom
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57
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Ramegowda V, Mysore KS, Senthil-Kumar M. Virus-induced gene silencing is a versatile tool for unraveling the functional relevance of multiple abiotic-stress-responsive genes in crop plants. FRONTIERS IN PLANT SCIENCE 2014; 5:323. [PMID: 25071806 PMCID: PMC4085877 DOI: 10.3389/fpls.2014.00323] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 06/19/2014] [Indexed: 05/03/2023]
Abstract
Virus-induced gene silencing (VIGS) is an effective tool for gene function analysis in plants. Over the last decade, VIGS has been successfully used as both a forward and reverse genetics technique for gene function analysis in various model plants, as well as crop plants. With the increased identification of differentially expressed genes under various abiotic stresses through high-throughput transcript profiling, the application of VIGS is expected to be important in the future for functional characterization of a large number of genes. In the recent past, VIGS was proven to be an elegant tool for functional characterization of genes associated with abiotic stress responses. In this review, we provide an overview of how VIGS is used in different crop species to characterize genes associated with drought-, salt-, oxidative- and nutrient-deficiency-stresses. We describe the examples from studies where abiotic stress related genes are characterized using VIGS. In addition, we describe the major advantages of VIGS over other currently available functional genomics tools. We also summarize the recent improvements, limitations and future prospects of using VIGS as a tool for studying plant responses to abiotic stresses.
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Affiliation(s)
- Venkategowda Ramegowda
- Department of Crop Physiology, University of Agricultural Sciences, GKVKBangalore, India
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58
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Harper S, Cowell S, Robertson C, Dawson W. Differential tropism in roots and shoots infected by Citrus tristeza virus. Virology 2014; 460-461:91-9. [DOI: 10.1016/j.virol.2014.04.035] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Revised: 04/06/2014] [Accepted: 04/19/2014] [Indexed: 10/25/2022]
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59
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Santovito E, Mascia T, Siddiqui SA, Minutillo SA, Valkonen JPT, Gallitelli D. Infection cycle of Artichoke Italian latent virus in tobacco plants: meristem invasion and recovery from disease symptoms. PLoS One 2014; 9:e99446. [PMID: 24911029 PMCID: PMC4050035 DOI: 10.1371/journal.pone.0099446] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Accepted: 05/14/2014] [Indexed: 11/18/2022] Open
Abstract
Nepoviral infections induce recovery in fully expanded leaves but persist in shoot apical meristem (SAM) by a largely unknown mechanism. The dynamics of infection of a grapevine isolate of Artichoke Italian latent virus (AILV-V, genus Nepovirus) in tobacco plants, including colonization of SAM, symptom induction and subsequent recovery of mature leaves from symptoms, were characterized. AILV-V moved from the inoculated leaves systemically and invaded SAM in 7 days post-inoculation (dpi), remaining detectable in SAM at least up to 40 dpi. The new top leaves recovered from viral symptoms earliest at 21 dpi. Accumulation of viral RNA to a threshold level was required to trigger the overexpression of RDR6 and DCL4. Consequently, accumulation of viral RNA decreased in the systemically infected leaves, reaching the lowest concentration in the 3rd and 4th leaves at 23 dpi, which was concomitant with recovery of the younger, upper leaves from disease symptoms. No evidence of virus replication was found in the recovered leaves, but they contained infectious virus particles and were protected against re-inoculation with AILV-V. In this study we also showed that AILV-V did not suppress initiation or maintenance of RNA silencing in transgenic plants, but was able to interfere with the cell-to-cell movement of the RNA silencing signal. Our results suggest that AILV-V entrance in SAM and activation of RNA silencing may be distinct processes since the latter is triggered in fully expanded leaves by the accumulation of viral RNA above a threshold level rather than by virus entrance in SAM.
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Affiliation(s)
- Elisa Santovito
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy
| | - Tiziana Mascia
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy
- Istituto di Virologia vegetale del Consiglio Nazionale della Ricerca, Unità Operativa di Supporto di Bari, Bari, Italy
| | - Shahid A. Siddiqui
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland
| | - Serena Anna Minutillo
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy
| | - Jari P. T. Valkonen
- Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland
| | - Donato Gallitelli
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy
- Istituto di Virologia vegetale del Consiglio Nazionale della Ricerca, Unità Operativa di Supporto di Bari, Bari, Italy
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60
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Bilichak A, Yao Y, Kovalchuk I. Transient down-regulation of the RNA silencing machinery increases efficiency of Agrobacterium-mediated transformation of Arabidopsis. PLANT BIOTECHNOLOGY JOURNAL 2014; 12:590-600. [PMID: 24472037 DOI: 10.1111/pbi.12165] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Accepted: 12/15/2013] [Indexed: 06/03/2023]
Abstract
Agrobacterium tumefaciens is a plant pathogen that is widely used in plant transformation. As the process of transgenesis includes the delivery of single-stranded T-DNA molecule, we hypothesized that transformation rate may negatively correlate with the efficiency of the RNA-silencing machinery. Using mutants compromised in either the transcriptional or post-transcriptional gene-silencing pathways, two inhibitors of stable transformation were revealed-AGO2 and NRPD1a. Furthermore, an immunoprecipitation experiment has shown that NRPD1, a subunit of Pol IV, directly interacts with Agrobacterium T-DNA in planta. Using the Tobacco rattle virus (TRV)--based virus-induced gene silencing (VIGS) technique, we demonstrated that the transient down-regulation of the expression of either AGO2 or NRPD1a genes in reproductive organs of Arabidopsis, leads to an increase in transformation rate. We observed a 6.0- and 3.5-fold increase in transformation rate upon transient downregulation of either AGO2 or NRPD1a genes, respectively. This is the first report demonstrating the increase in the plant transformation rate via VIGS-mediated transient down-regulation of the components of epigenetic machinery in reproductive tissue.
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MESH Headings
- Agrobacterium/physiology
- Arabidopsis/genetics
- Arabidopsis/microbiology
- Arabidopsis Proteins/metabolism
- Blotting, Southern
- DNA Breaks, Double-Stranded
- DNA Methylation/genetics
- DNA, Bacterial/genetics
- DNA-Directed RNA Polymerases/metabolism
- Down-Regulation
- Epigenesis, Genetic
- Genes, Plant
- Genetic Loci
- Models, Genetic
- Mutation/genetics
- Plants, Genetically Modified
- Protein Binding
- Protein Subunits/metabolism
- RNA Interference
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Small Interfering/metabolism
- Reverse Genetics
- Transformation, Genetic
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Affiliation(s)
- Andriy Bilichak
- Department of Biological Sciences, University of Lethbridge, Lethbridge, AB, Canada
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61
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Sha A, Zhao J, Yin K, Tang Y, Wang Y, Wei X, Hong Y, Liu Y. Virus-based microRNA silencing in plants. PLANT PHYSIOLOGY 2014; 164:36-47. [PMID: 24296072 PMCID: PMC3875814 DOI: 10.1104/pp.113.231100] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Accepted: 11/30/2013] [Indexed: 05/18/2023]
Abstract
MicroRNAs (miRNAs) play pivotal roles in various biological processes across kingdoms. Many plant miRNAs have been experimentally identified or predicted by bioinformatics mining of small RNA databases. However, the functions of these miRNAs remain largely unknown due to the lack of effective genetic tools. Here, we report a virus-based microRNA silencing (VbMS) system that can be used for functional analysis of plant miRNAs. VbMS is performed through tobacco rattle virus-based expression of miRNA target mimics to silence endogenous miRNAs. VbMS of either miR172 or miR165/166 caused developmental defects in Nicotiana benthamiana. VbMS of miR319 reduced the complexity of tomato (Solanum lycopersicum) compound leaves. These results demonstrate that tobacco rattle virus-based VbMS is a powerful tool to silence endogenous miRNAs and to dissect their functions in different plant species.
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Affiliation(s)
| | | | | | | | - Yan Wang
- MOE Key Laboratory of Bioinformatics, Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China (A.S., J.Z., K.Y., Y.T., Y.W., X.W., Y.L.)
- Institute of Oil Crops Research, Chinese Academy of Agriculture Sciences, Wuhan 430062, China (A.S.); and
- Research Centre for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China (Y.H.)
| | - Xiang Wei
- MOE Key Laboratory of Bioinformatics, Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China (A.S., J.Z., K.Y., Y.T., Y.W., X.W., Y.L.)
- Institute of Oil Crops Research, Chinese Academy of Agriculture Sciences, Wuhan 430062, China (A.S.); and
- Research Centre for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China (Y.H.)
| | - Yiguo Hong
- MOE Key Laboratory of Bioinformatics, Center for Plant Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China (A.S., J.Z., K.Y., Y.T., Y.W., X.W., Y.L.)
- Institute of Oil Crops Research, Chinese Academy of Agriculture Sciences, Wuhan 430062, China (A.S.); and
- Research Centre for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou 310036, China (Y.H.)
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62
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Shaw J, Love AJ, Makarova SS, Kalinina NO, Harrison BD, Taliansky ME. Coilin, the signature protein of Cajal bodies, differentially modulates the interactions of plants with viruses in widely different taxa. Nucleus 2014; 5:85-94. [PMID: 24637832 PMCID: PMC4028359 DOI: 10.4161/nucl.28315] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2013] [Revised: 02/18/2014] [Accepted: 02/21/2014] [Indexed: 12/28/2022] Open
Abstract
Cajal bodies (CBs) are distinct nuclear bodies physically and functionally associated with the nucleolus. In addition to their traditional function in coordinating maturation of certain nuclear RNAs, CBs participate in cell cycle regulation, development, and regulation of stress responses. A key "signature" component of CBs is coilin, the scaffolding protein essential for CB formation and function. Using an RNA silencing (loss-of-function) approach, we describe here new phenomena whereby coilin also affects, directly or indirectly, a variety of interactions between host plants and viruses that have RNA or DNA genomes. Moreover, the effects of coilin on these interactions are manifested differently: coilin contributes to plant defense against tobacco rattle virus (tobravirus), tomato black ring virus (nepovirus), barley stripe mosaic virus (hordeivirus), and tomato golden mosaic virus (begomovirus). In contrast, with potato virus Y (potyvirus) and turnip vein clearing virus (tobamovirus), coilin serves to increase virus pathogenicity. These findings show that interactions with coilin (or CBs) may involve diverse mechanisms with different viruses and that these mechanisms act at different phases of virus infection. Thus, coilin (CBs) has novel, unexpected natural functions that may be recruited or subverted by plant viruses for their own needs or, in contrast, are involved in plant defense mechanisms that suppress host susceptibility to the viruses.
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Affiliation(s)
- Jane Shaw
- Cell and Molecular Sciences; The James Hutton Institute; Dundee, UK
| | - Andrew J Love
- Cell and Molecular Sciences; The James Hutton Institute; Dundee, UK
| | - Svetlana S Makarova
- AN Belozersky Institute of Physico-Chemical Biology; Moscow State University; Moscow, Russia
| | - Natalia O Kalinina
- AN Belozersky Institute of Physico-Chemical Biology; Moscow State University; Moscow, Russia
| | - Bryan D Harrison
- Cell and Molecular Sciences; The James Hutton Institute; Dundee, UK
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63
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Sun L, Andika IB, Shen J, Yang D, Ratti C, Chen J. The CUG-initiated larger form coat protein of Chinese wheat mosaic virus binds to the cysteine-rich RNA silencing suppressor. Virus Res 2013; 177:66-74. [DOI: 10.1016/j.virusres.2013.07.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Revised: 07/16/2013] [Accepted: 07/18/2013] [Indexed: 12/19/2022]
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64
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Farrow SC, Facchini PJ. Dioxygenases catalyze O-demethylation and O,O-demethylenation with widespread roles in benzylisoquinoline alkaloid metabolism in opium poppy. J Biol Chem 2013; 288:28997-9012. [PMID: 23928311 DOI: 10.1074/jbc.m113.488585] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
In opium poppy, the antepenultimate and final steps in morphine biosynthesis are catalyzed by the 2-oxoglutarate/Fe(II)-dependent dioxygenases, thebaine 6-O-demethylase (T6ODM) and codeine O-demethylase (CODM). Further investigation into the biochemical functions of CODM and T6ODM revealed extensive and unexpected roles for such enzymes in the metabolism of protopine, benzo[c]phenanthridine, and rhoeadine alkaloids. When assayed with a wide range of benzylisoquinoline alkaloids, CODM, T6ODM, and the functionally unassigned paralog DIOX2, renamed protopine O-dealkylase, showed novel and efficient dealkylation activities, including regio- and substrate-specific O-demethylation and O,O-demethylenation. Enzymes catalyzing O,O-demethylenation, which cleave a methylenedioxy bridge leaving two hydroxyl groups, have previously not been reported in plants. Similar cleavage of methylenedioxy bridges on substituted amphetamines is catalyzed by heme-dependent cytochromes P450 in mammals. Preferred substrates for O,O-demethylenation by CODM and protopine O-dealkylase were protopine alkaloids that serve as intermediates in the biosynthesis of benzo[c]phenanthridine and rhoeadine derivatives. Virus-induced gene silencing used to suppress the abundance of CODM and/or T6ODM transcripts indicated a direct physiological role for these enzymes in the metabolism of protopine alkaloids, and they revealed their indirect involvement in the formation of the antimicrobial benzo[c]phenanthridine sanguinarine and certain rhoeadine alkaloids in opium poppy.
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Affiliation(s)
- Scott C Farrow
- From the Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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65
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Agüero J, Vives MC, Velázquez K, Ruiz-Ruiz S, Juárez J, Navarro L, Moreno P, Guerri J. Citrus leaf blotch virus invades meristematic regions in Nicotiana benthamiana and citrus. MOLECULAR PLANT PATHOLOGY 2013; 14:610-6. [PMID: 23560714 PMCID: PMC6638833 DOI: 10.1111/mpp.12031] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
To invade systemically host plants, viruses need to replicate in the infected cells, spread to neighbouring cells through plasmodesmata and move to distal parts of the plant via sieve tubes to start new infection foci. To monitor the infection of Nicotiana benthamiana plants by Citrus leaf blotch virus (CLBV), leaves were agroinoculated with an infectious cDNA clone of the CLBV genomic RNA expressing green fluorescent protein (GFP) under the transcriptional control of a duplicate promoter of the coat protein subgenomic RNA. Fluorescent spots first appeared in agroinfiltrated leaves 11-12 days after infiltration, indicating CLBV replication. Then, after entering the phloem vascular system, CLBV was unloaded in the upper parts of the plant and invaded all tissues, including flower organs and meristems. GFP fluorescence was not visible in citrus plants infected with CLBV-GFP. Therefore, to detect CLBV in meristematic regions, Mexican lime (Citrus aurantifolia) plants were graft inoculated with CLBV, with Citrus tristeza virus (CTV), a virus readily eliminated by shoot-tip grafting in vitro, or with both simultaneously. Although CLBV was detected by hybridization and real-time reverse transcription-polymerase chain reaction (RT-PCR) in 0.2-mm shoot tips in all CLBV-inoculated plants, CTV was not detected. These results explain the difficulty in eliminating CLBV by shoot-tip grafting in vitro.
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Affiliation(s)
- Jesús Agüero
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias-IVIA, Moncada, Valencia 46113, Spain
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66
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Murray GGR, Kosakovsky Pond SL, Obbard DJ. Suppressors of RNAi from plant viruses are subject to episodic positive selection. Proc Biol Sci 2013; 280:20130965. [PMID: 23804618 PMCID: PMC3712444 DOI: 10.1098/rspb.2013.0965] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Viral suppressors of RNAi (VSRs) are proteins that actively inhibit the antiviral RNA interference (RNAi) immune response, providing an immune evasion route for viruses. It has been hypothesized that VSRs are engaged in a molecular ‘arms race’ with RNAi pathway genes. Two lines of evidence support this. First, VSRs from plant viruses display high sequence diversity, and are frequently gained and lost over evolutionary time scales. Second, Drosophila antiviral RNAi genes show high rates of adaptive evolution. Here, we investigate whether VSRs diversify faster than other genes and, if so, whether this is a result of positive selection, as might be expected in an arms race. By analysis of 12 plant RNA viruses, we show that the relative rate of protein evolution is higher for VSRs than for other genes, but that this is not attributable to pervasive positive selection. We argue that, because evolutionary time scales are extremely different for viruses and eukaryotes, it is improbable that viral adaptation (as measured by the ratio of non-synonymous to synonymous change) will be dominated by one-to-one coevolution with eukaryotes. Instead, for plant virus VSRs, we find strong evidence of episodic selection—diversifying selection that acts on a subset of lineages—which might be attributable to frequent shifts between different host genotypes or species.
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Affiliation(s)
- Gemma G R Murray
- Centre for Infection Immunity and Evolution, Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK.
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67
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Deng X, Kelloniemi J, Haikonen T, Vuorinen AL, Elomaa P, Teeri TH, Valkonen JPT. Modification of Tobacco rattle virus RNA1 to serve as a VIGS vector reveals that the 29K movement protein is an RNA silencing suppressor of the virus. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2013; 26:503-14. [PMID: 23360458 DOI: 10.1094/mpmi-12-12-0280-r] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Tobacco rattle virus (TRV) has a bipartite, positive-sense single-stranded RNA genome and is widely used for virus-induced gene silencing (VIGS) in plants. RNA1 of TRV that lacks the gene for the cysteine-rich 16K silencing-suppression protein infects plants systemically in the absence of RNA2. Here, we attempted to engineer RNA1 for use as a VIGS vector by inserting heterologous gene fragments to replace 16K. The RNA1 vector systemically silenced the phytoene desaturase (PDS) gene, although less efficiently than when the original VIGS vector system was used, which consists of wild-type RNA1 and engineered RNA2 carrying the heterologous gene. Infectious RNA1 mutants with a dysfunctional 16K suppressed silencing and enhanced transgene expression in green fluorescent protein-transgenic Nicotiana benthamiana following inoculation by agroinfiltration, unlike mutants that also lacked 29K, a movement protein (MP) gene. The 30K MP gene of Tobacco mosaic virus complemented in cis the movement defect but not the silencing suppression functions of TRV 29K. Silencing suppression by 29K occurred in the context of RNA1 replication but not in an agroinfiltration assay which tested 29K alone for suppression of sense-mediated silencing. Both 29K and 16K were needed to avoid necrotic symptoms in RNA1-infected N. benthamiana. The results shed new light on virulence factors of TRV.
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Affiliation(s)
- Xianbao Deng
- Department of Agricultural Sciences, University of Helsinki, Finland
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68
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Sun L, Andika IB, Kondo H, Chen J. Identification of the amino acid residues and domains in the cysteine-rich protein of Chinese wheat mosaic virus that are important for RNA silencing suppression and subcellular localization. MOLECULAR PLANT PATHOLOGY 2013; 14:265-78. [PMID: 23458485 PMCID: PMC6638639 DOI: 10.1111/mpp.12002] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Cysteine-rich proteins (CRPs) encoded by some plant viruses in diverse genera function as RNA silencing suppressors. Within the N-terminal portion of CRPs encoded by furoviruses, there are six conserved cysteine residues and a Cys-Gly-X-X-His motif (Cys, cysteine; Gly, glycine; His, histidine; X, any amino acid residue) with unknown function. The central domains contain coiled-coil heptad amino acid repeats that usually mediate protein dimerization. Here, we present evidence that the conserved cysteine residues and Cys-Gly-X-X-His motif in the CRP of Chinese wheat mosaic virus (CWMV) are critical for protein stability and silencing suppression activity. Mutation of a leucine residue in the third coiled-coil heptad impaired CWMV CRP activity for suppression of local silencing, but not for the promotion of cell-to-cell movement of Potato virus X (PVX). In planta and in vitro analysis of wild-type and mutant proteins indicated that the ability of the CRP to self-interact was correlated with its suppression activity. Deletion of up to 40 amino acids at the C-terminus did not abolish suppression activity, but disrupted the association of CRP with endoplasmic reticulum (ER), and reduced its activity in the enhancement of PVX symptom severity. Interestingly, a short region in the C-terminal domain, predicted to form an amphipathic α-helical structure, was responsible for the association of CWMV CRP with ER. Overall, our results demonstrate that the N-terminal and central regions are the functional domains for suppression activity, whereas the C-terminal region primarily functions to target CWMV CRP to the ER.
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Affiliation(s)
- Liying Sun
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Ministry of Agriculture Key Laboratory of Biotechnology in Plant Protection, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
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69
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Desgagné-Penix I, Facchini PJ. Systematic silencing of benzylisoquinoline alkaloid biosynthetic genes reveals the major route to papaverine in opium poppy. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2012; 72:331-44. [PMID: 22725256 DOI: 10.1111/j.1365-313x.2012.05084.x] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Papaverine, a major benzylisoquinoline alkaloid in opium poppy (Papaver somniferum), is used as a vasodilator and antispasmodic. Conversion of the initial intermediate (S)-norcoclaurine to papaverine involves 3'-hydroxylation, four O-methylations and dehydrogenation. However, our understanding of papaverine biosynthesis remains controversial more than a century after an initial scheme was proposed. In vitro assays and in vivo labeling studies have been insufficient to establish the sequence of conversions, the potential role of the intermediate (S)-reticuline, and the enzymes involved. We used virus-induced gene silencing in opium poppy to individually suppress the expression of six genes with putative roles in papaverine biosynthesis. Suppression of the gene encoding coclaurine N-methyltransferase dramatically increased papaverine levels at the expense of N-methylated alkaloids, indicating that the main biosynthetic route to papaverine proceeds via N-desmethylated compounds rather than through (S)-reticuline. Suppression of genes encoding (S)-3'-hydroxy-N-methylcoclaurine 4-O-methyltransferase and norreticuline 7-O-methyltransferase, which accept certain N-desmethylated alkaloids, reduced papaverine content. In contrast, suppression of genes encoding N-methylcoclaurine 3'-hydroxylase or reticuline 7-O-methyltransferase, which are specific for N-methylated alkaloids, did not affect papaverine levels. Suppression of norcoclaurine 6-O-methyltransferase transcript levels significantly suppressed total alkaloid accumulation, implicating (S)-coclaurine as a key branch-point intermediate. The differential detection of N-desmethylated compounds in response to suppression of specific genes highlights the primary route to papaverine.
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Affiliation(s)
- Isabel Desgagné-Penix
- Department of Biological Sciences, University of Calgary, Calgary, AB T2N 1N4, Canada
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70
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Andika IB, Kondo H, Nishiguchi M, Tamada T. The cysteine-rich proteins of beet necrotic yellow vein virus and tobacco rattle virus contribute to efficient suppression of silencing in roots. J Gen Virol 2012; 93:1841-1850. [PMID: 22647371 DOI: 10.1099/vir.0.043513-0] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many plant viruses encode proteins that suppress RNA silencing, but little is known about the activity of silencing suppressors in roots. This study examined differences in the silencing suppression activity of different viruses in leaves and roots of Nicotiana benthamiana plants. Infection by tobacco mosaic virus, potato virus Y and cucumber mosaic virus but not potato virus X (PVX) resulted in strong silencing suppression activity of a transgene in both leaves and roots, whereas infection by beet necrotic yellow vein virus (BNYVV) and tobacco rattle virus (TRV) showed transgene silencing suppression in roots but not in leaves. For most viruses tested, viral negative-strand RNA accumulated at a very low level in roots, compared with considerable levels of positive-strand genomic RNA. Co-inoculation of leaves with PVX and either BNYVV or TRV produced an increase in PVX negative-strand RNA and subgenomic RNA (sgRNA) accumulation in roots. The cysteine-rich proteins (CRPs) BNYVV p14 and TRV 16K showed weak silencing suppression activity in leaves. However, when either of these CRPs was expressed from a PVX vector, there was an enhancement of PVX negative-strand RNA and sgRNA accumulation in roots compared with PVX alone. Such enhancement of PVX sgRNAs was also observed by expression of CRPs of other viruses and the well-known suppressors HC-Pro and p19 but not of the potato mop-top virus p8 CRP. These results indicate that BNYVV- and TRV-encoded CRPs suppress RNA silencing more efficiently in roots than in leaves.
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Affiliation(s)
- Ida Bagus Andika
- Institute of Plant Science and Resources (IPSR), Okayama University, Kurashiki 710-0046, Japan
| | - Hideki Kondo
- Institute of Plant Science and Resources (IPSR), Okayama University, Kurashiki 710-0046, Japan
| | | | - Tetsuo Tamada
- Institute of Plant Science and Resources (IPSR), Okayama University, Kurashiki 710-0046, Japan
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71
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Larsen JS, Curtis WR. RNA viral vectors for improved Agrobacterium-mediated transient expression of heterologous proteins in Nicotiana benthamiana cell suspensions and hairy roots. BMC Biotechnol 2012; 12:21. [PMID: 22559055 PMCID: PMC3403893 DOI: 10.1186/1472-6750-12-21] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Accepted: 05/06/2012] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND Plant cell suspensions and hairy root cultures represent scalable protein expression platforms. Low protein product titers have thus far limited the application of transient protein expression in these hosts. The objective of this work was to overcome this limitation by harnessing A. tumefaciens to deliver replicating and non-replicating RNA viral vectors in plant tissue co-cultures. RESULTS Replicating vectors derived from Potato virus X (PVX) and Tobacco rattle virus (TRV) were modified to contain the reporter gene β-glucuronidase (GUS) with a plant intron to prevent bacterial expression. In cell suspensions, a minimal PVX vector retaining only the viral RNA polymerase gene yielded 6.6-fold more GUS than an analogous full-length PVX vector. Transient co-expression of the minimal PVX vector with P19 of Tomato bushy stunt virus or HC-Pro of Tobacco etch virus to suppress post-transcriptional gene silencing increased GUS expression by 44 and 83%, respectively. A non-replicating vector containing a leader sequence from Cowpea mosaic virus (CPMV-HT) modified for enhanced translation led to 70% higher transient GUS expression than a control treatment. In hairy roots, a TRV vector capable of systemic movement increased GUS accumulation by 150-fold relative to the analogous PVX vector. Histochemical staining for GUS in TRV-infected hairy roots revealed the capacity for achieving even higher productivity per unit biomass. CONCLUSIONS For the first time, replicating PVX vectors and a non-replicating CPMV-HT vector were successfully applied toward transient heterologous protein expression in cell suspensions. A replicating TRV vector achieved transient GUS expression levels in hairy roots more than an order of magnitude higher than the highest level previously reported with a viral vector delivered by A. tumefaciens.
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Affiliation(s)
- Jeffrey S Larsen
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA
| | - Wayne R Curtis
- Department of Chemical Engineering, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA
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72
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Wang LY, Lin SS, Hung TH, Li TK, Lin NC, Shen TL. Multiple domains of the tobacco mosaic virus p126 protein can independently suppress local and systemic RNA silencing. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2012; 25:648-57. [PMID: 22324815 DOI: 10.1094/mpmi-06-11-0155] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Small RNA-mediated RNA silencing is a widespread antiviral mechanism in plants and other organisms. Many viruses encode suppressors of RNA silencing for counter-defense. The p126 protein encoded by Tobacco mosaic virus (TMV) has been reported to be a suppressor of RNA silencing but the mechanism of its function remains unclear. This protein is unique among the known plant viral silencing suppressors because of its large size and multiple domains. Here, we report that the methyltransferase, helicase, and nonconserved region II (NONII) of p126 each has silencing-suppressor function. The silencing-suppression activities of methyltransferase and helicase can be uncoupled from their enzyme activities. Specific amino acids in NONII previously shown to be crucial for viral accumulation and symptom development are also crucial for silencing suppression. These results suggest that some viral proteins have evolved to possess modular structural domains that can independently interfere with host silencing, and that this may be an effective mechanism of increasing the robustness of a virus.
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Affiliation(s)
- Li-Ya Wang
- Department of Plant Pathology and Microbiology, College of Bioresources and Agriculture, National Taiwan University, Taipei, Taiwan
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73
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Zhu H, Guo H. The role of virus-derived small interfering RNAs in RNA silencing in plants. SCIENCE CHINA-LIFE SCIENCES 2012; 55:119-25. [DOI: 10.1007/s11427-012-4281-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 12/28/2011] [Indexed: 01/09/2023]
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74
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Renovell Á, Vives MC, Ruiz-Ruiz S, Navarro L, Moreno P, Guerri J. The Citrus leaf blotch virus movement protein acts as silencing suppressor. Virus Genes 2012; 44:131-40. [PMID: 21948005 DOI: 10.1007/s11262-011-0674-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 09/12/2011] [Indexed: 01/25/2023]
Abstract
To counteract plant antiviral defense based on RNA silencing, many viruses express proteins that inhibit this mechanism at different levels. The genome of Citrus leaf blotch virus (CLBV) encodes a 227-kDa protein involved in replication, a 40-kDa movement protein (MP), and a 41-kDa coat protein (CP). To determine if any of these proteins might have RNA silencing suppressor activities, we have used Agrobacterium-mediated transient assays in the green fluorescent protein (GFP)-expressing Nicotiana benthamiana line 16c. Only CLBV MP was able to suppress intracellular GFP silencing induced by expression of either single- or double-stranded (ds) GFP RNA, but not cell-to-cell or long distance spread of the silencing signal. The MP suppressor activity was weak compared to other characterized viral suppressor proteins. Overall our data indicate that MP acts as a suppressor of local silencing probably by interfering in the silencing pathway downstream of the steps of dsRNA and small RNAs generation.
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Affiliation(s)
- Águeda Renovell
- Centro de Protección Vegetal y Biotecnología, Instituto Valenciano de Investigaciones Agrarias, Ctra. Moncada-Náquera Km. 4.5, 46113 Moncada, Valencia, Spain
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75
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Mobile FT mRNA contributes to the systemic florigen signalling in floral induction. Sci Rep 2011; 1:73. [PMID: 22355592 PMCID: PMC3216560 DOI: 10.1038/srep00073] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2011] [Accepted: 08/05/2011] [Indexed: 12/13/2022] Open
Abstract
In inducing photoperiodic conditions, plants produce a signal dubbed "florigen" in leaves. Florigen moves through the phloem to the shoot apical meristem (SAM) where it induces flowering. In Arabidopsis, the FLOWERING LOCUS T (FT) protein acts as a component of this phloem-mobile signal. However whether the transportable FT mRNA also contributes to systemic florigen signalling remains to be elucidated. Using non-conventional approaches that exploit virus-induced RNA silencing and meristem exclusion of virus infection, we demonstrated that the ArabidopsisFT mRNA, independent of the FT protein, can move into the SAM. Viral ectopic expression of a non-translatable FT mRNA promoted earlier flowering in the short-day (SD) Nicotiana tabacum Maryland Mammoth tobacco in SD. These data suggest a possible role for FT mRNA in systemic floral signalling, and also demonstrate that cis-transportation of cellular mRNA into SAM and meristem exclusion of pathogenic RNAs are two mechanistically distinct processes.
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76
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Jaubert M, Bhattacharjee S, Mello AF, Perry KL, Moffett P. ARGONAUTE2 mediates RNA-silencing antiviral defenses against Potato virus X in Arabidopsis. PLANT PHYSIOLOGY 2011; 156:1556-64. [PMID: 21576511 PMCID: PMC3135937 DOI: 10.1104/pp.111.178012] [Citation(s) in RCA: 143] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Accepted: 05/14/2011] [Indexed: 05/18/2023]
Abstract
RNA-silencing mechanisms control many aspects of gene regulation including the detection and degradation of viral RNA through the action of, among others, Dicer-like and Argonaute (AGO) proteins. However, the extent to which RNA silencing restricts virus host range has been difficult to separate from other factors that can affect virus-plant compatibility. Here we show that Potato virus X (PVX) can infect Arabidopsis (Arabidopsis thaliana), which is normally a nonhost for PVX, if coinfected with a second virus, Pepper ringspot virus. Here we show that the pepper ringspot virus 12K protein functions as a suppressor of silencing that appears to enable PVX to infect Arabidopsis. We also show that PVX is able to infect Arabidopsis Dicer-like mutants, indicating that RNA silencing is responsible for Arabidopsis nonhost resistance to PVX. Furthermore, we find that restriction of PVX on Arabidopsis also depends on AGO2, suggesting that this AGO protein has evolved to specialize in antiviral defenses.
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Affiliation(s)
| | | | | | | | - Peter Moffett
- Boyce Thompson Institute for Plant Research, Ithaca, New York 14853 (M.J., S.B., P.M.); Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, New York 14853 (A.F.S.M., K.L.P.); Centre de Recherche en Amélioration Végétale, Département de Biologie, Université de Sherbrooke, Sherbrooke, Quebec, Canada J1K 2R1 (P.M.)
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77
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Siddiqui SA, Valkonen JPT, Rajamäki ML, Lehto K. The 2b silencing suppressor of a mild strain of Cucumber mosaic virus alone is sufficient for synergistic interaction with Tobacco mosaic virus and induction of severe leaf malformation in 2b-transgenic tobacco plants. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2011; 24:685-93. [PMID: 21341985 DOI: 10.1094/mpmi-12-10-0290] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Tobacco plants infected simultaneously by Tobacco mosaic virus (TMV) and Cucumber mosaic virus (CMV) are known to produce a specific synergistic disease in which the emerging leaves are filiformic. Similar developmental malformations are also caused to a lesser extent by the severe strains (e.g., Fny) of CMV alone, but mild strains (e.g., Kin) cause them only in mixed infection with TMV. We show here that transgenic tobacco plants expressing 2b protein of CMV-Kin produce filiformic symptoms when infected with TMV, indicating that only 2b protein is needed from CMV-Kin for this synergistic relationship. On the other hand, transgenic plants that express either the wild-type TMV genome or a modified TMV genome with its coat protein deleted or movement protein (MP) inactivated also develop filiformic or at least distinctly narrow leaves, while plants expressing the MP alone do not develop any malformations when infected with CMV-Kin. These results show that either TMV helicase/replicase protein or active TMV replication are required for this synergistic effect. The effect appears to be related to an efficient depletion of silencing machinery, caused jointly by both viral silencing suppressors, i.e., CMV 2b protein and the TMV 126-kDa replicase subunit.
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Affiliation(s)
- Shahid A Siddiqui
- Department of Agricultural Sciences, University of Helsinki, Finland
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78
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Molnar A, Melnyk C, Baulcombe DC. Silencing signals in plants: a long journey for small RNAs. Genome Biol 2011; 12:215. [PMID: 21235831 PMCID: PMC3091295 DOI: 10.1186/gb-2010-11-12-219] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Recent research shows that short RNA molecules act as mobile signals that direct mRNA cleavage and DNA methylation in recipient cells.
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Affiliation(s)
- Attila Molnar
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK.
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79
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Molnar A, Melnyk C, Baulcombe DC. Silencing signals in plants: a long journey for small RNAs. Genome Biol 2011. [PMID: 21235831 DOI: 10.1186/gb-2010-ll-12-219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023] Open
Abstract
Recent research shows that short RNA molecules act as mobile signals that direct mRNA cleavage and DNA methylation in recipient cells.
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Affiliation(s)
- Attila Molnar
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK.
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80
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Benitez-Alfonso Y, Faulkner C, Ritzenthaler C, Maule AJ. Plasmodesmata: gateways to local and systemic virus infection. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2010; 23:1403-12. [PMID: 20687788 DOI: 10.1094/mpmi-05-10-0116] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
As channels that provide cell-to-cell connectivity, plasmodesmata are central to the local and systemic spread of viruses in plants. This review discusses the current state of knowledge of the structure and function of these channels and the ways in which viruses bring about functional changes that allow macromolecular trafficking to occur. Despite the passing of two decades since the first identification of a viral movement protein that mediates these changes, our understanding of the relevant molecular mechanisms remains in its infancy. However, viral movement proteins provide valuable tools for the modification of plasmodesmata and will continue to assist in the dissection of plasmodesmal properties in relation to their core roles in cell-to-cell communication.
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81
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Nawaz-Ul-Rehman MS, Nahid N, Mansoor S, Briddon RW, Fauquet CM. Post-transcriptional gene silencing suppressor activity of two non-pathogenic alphasatellites associated with a begomovirus. Virology 2010; 405:300-8. [PMID: 20598726 DOI: 10.1016/j.virol.2010.06.024] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2010] [Revised: 04/24/2010] [Accepted: 06/08/2010] [Indexed: 11/25/2022]
Abstract
Alphasatellites and betasatellites are begomovirus-associated single-stranded circular DNA molecules. Two distinct alphasatellites, Gossypium darwinii symptomless alphasatellite and Gossypium mustelinium symptomless alphasatellite, were previously isolated from Gossypium davidsonii and G.mustelinium. Here we show that the replication-associated proteins (Rep: a rolling-circle replication initiator protein) encoded by these alphasatellites interact with the Rep and C4 proteins encoded by their helper begomovirus, Cotton leaf curl Rajasthan virus (CLCuRaV), in a yeast two-hybrid assay. Both the alphasatellite-encoded Reps were found to have strong gene silencing suppressor activity, in contrast to the betasatellite-encoded betaC1 and CLCuRaV-encoded C2, C4 and V2 proteins. The presence of alphasatellites maintained suppression of gene silencing in the youngest, actively growing tissue of CLCuRaV-betasatellite-infected plants. This is the first demonstration of a rolling-circle replication initiator protein with suppressor of gene silencing activity and provides a possible explanation for the selective advantage provided by the association of alphasatellites with begomovirus-betasatellite complexes.
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82
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Abstract
The tobraviruses, Tobacco rattle virus (TRV), Pea early-browning virus (PEBV) and Pepper ringspot virus (PepRSV), are positive-strand RNA viruses with rod-shaped virus particles that are transmitted between plants by trichodorid nematodes. As a group, these viruses infect many plant species, with TRV having the widest host range. Recent studies have begun to dissect the interaction of TRV with potato, currently the most commercially important crop disease caused by any of the tobraviruses. As well as being successful plant pathogens, these viruses have become widely used as vectors for expression in plants of nonviral proteins or, more frequently, as initiators of virus-induced gene silencing (VIGS). Precisely why tobraviruses should be so effective as VIGS vectors is not known; however, molecular studies of the mode of action of the tobravirus silencing suppressor protein are shedding some light on this process.
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83
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RNAi-mediated viral immunity requires amplification of virus-derived siRNAs in Arabidopsis thaliana. Proc Natl Acad Sci U S A 2009; 107:484-9. [PMID: 19966292 DOI: 10.1073/pnas.0904086107] [Citation(s) in RCA: 303] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
In diverse eukaryotic organisms, Dicer-processed, virus-derived small interfering RNAs direct antiviral immunity by RNA silencing or RNA interference. Here we show that in addition to core dicing and slicing components of RNAi, the RNAi-mediated viral immunity in Arabidopsis thaliana requires host RNA-directed RNA polymerase (RDR) 1 or RDR6 to produce viral secondary siRNAs following viral RNA replication-triggered biogenesis of primary siRNAs. We found that the two antiviral RDRs exhibited specificity in targeting the tripartite positive-strand RNA genome of cucumber mosaic virus (CMV). RDR1 preferentially amplified the 5'-terminal siRNAs of each of the three viral genomic RNAs, whereas an increased production of siRNAs targeting the 3' half of RNA3 detected in rdr1 mutant plants appeared to be RDR6-dependent. However, siRNAs derived from a single-stranded 336-nucleotide satellite RNA of CMV were not amplified by either antiviral RDR, suggesting avoidance of the potent RDR-dependent silencing as a strategy for the molecular parasite of CMV to achieve preferential replication. Our work thus identifies a distinct mechanism for the amplification of immunity effectors, which together with the requirement for the biogenesis of endogenous siRNAs, may play a role in the emergence and expansion of eukaryotic RDRs.
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84
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Sunpapao A, Nakai T, Dong F, Mochizuki T, Ohki ST. The 2b protein of cucumber mosaic virus is essential for viral infection of the shoot apical meristem and for efficient invasion of leaf primordia in infected tobacco plants. J Gen Virol 2009; 90:3015-3021. [PMID: 19675191 DOI: 10.1099/vir.0.013219-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
It has been reported previously that a 2b protein-defective mutant of the cucumber mosaic virus (CMV) Pepo strain (Delta 2b) induces only mild symptoms in systemically infected tobacco plants. To clarify further the role of the 2b protein as an RNA silencing suppressor in mosaic symptom expression during CMV infection, this study monitored the sequential distribution of Delta 2b in the shoot meristem and leaf primordia (LP) of inoculated tobacco. Time-course histochemical observations revealed that Delta 2b was distributed in the shoot meristem at 7 days post-inoculation (p.i.), but could not invade shoot apical meristem (SAM) and quickly disappeared from the shoot meristem, whereas wild-type (Pepo) transiently appeared in SAM from 4 to 10 days p.i. In LP, Delta 2b signals were detected only at 14 and 21 days p.i., whereas dense Pepo signals were observed in LP from 4 to 18 days p.i. Northern blot analysis showed that small interfering RNA (siRNA) derived from Delta 2b RNA accumulated earlier in the shoot meristem and LP than that of Pepo. However, a similar amount of siRNA was detected in both Pepo- and Delta 2b-infected plants at late time points. Tissue printing analysis of the inoculated leaves indicated that the areas infected by Pepo increased faster than those infected by Delta 2b, whereas accumulation of Delta 2b in protoplasts was similar to that of Pepo. These findings suggest that the 2b protein of the CMV Pepo strain determines virulence by facilitating the distribution of CMV in the shoot meristem and LP via prevention of RNA silencing and/or acceleration of cell-to-cell movement.
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Affiliation(s)
- Anurag Sunpapao
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Takashi Nakai
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Fang Dong
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Tomofumi Mochizuki
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
| | - Satoshi T Ohki
- Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
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85
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Singh G, Popli S, Hari Y, Malhotra P, Mukherjee S, Bhatnagar RK. Suppression of RNA silencing by Flock house virus B2 protein is mediated through its interaction with the PAZ domain of Dicer. FASEB J 2009; 23:1845-57. [PMID: 19193719 DOI: 10.1096/fj.08-125120] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
RNA silencing is a conserved pathway that functions as an antiviral mechanism. The majority of viruses encode silencing suppressors that interfere with siRNA- and miRNA-guided silencing pathways. The insect flock house virus B2 protein (FHVB2) functions as an RNAi silencing suppressor that inhibits siRNA biogenesis. Here, we describe the generation of a GFP silent sensor line (Sf21) and a GFP sensor line expressing FHVB2 to study RNAi suppression mechanisms. Overexpression of FHVB2 resulted in suppression of GFP-RNAi and resumption of GFP expression. Protein fractionation studies with FHVB2-transfected cells showed that FHVB2 associates with a high-molecular-weight complex of Dicer and dsRNA/siRNAs. Yeast two-hybrid and pulldown assays revealed an interaction between FHVB2 and Drosophila Dicer proteins that appeared to involve PAZ domains. To map the FHVB2 domains interacting with Dicer, we used a 17-residue C-terminal deletion mutant. RNAi suppression was reversed in cells transfected with the FHVB2 mutant as revealed by loss of GFP. Additional yeast two-hybrid and in vitro pulldown assays confirmed that the C-terminal region of FHVB2 was involved in the interaction with the PAZ domains of Dicers. These results thus reveal a novel interaction between FHVB2 and Dicer that leads to suppression of siRNA biogenesis.
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Affiliation(s)
- Gatikrushna Singh
- International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi-110067, India
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86
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Díaz-Pendón JA, Ding SW. Direct and indirect roles of viral suppressors of RNA silencing in pathogenesis. ANNUAL REVIEW OF PHYTOPATHOLOGY 2008; 46:303-26. [PMID: 18680427 DOI: 10.1146/annurev.phyto.46.081407.104746] [Citation(s) in RCA: 159] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Plant and animal viruses overcome host antiviral silencing by encoding diverse viral suppressors of RNA silencing (VSRs). Prior to the identification and characterization of their silencing suppression activities mostly in transgene silencing assays, plant VSRs were known to enhance virus accumulation in the inoculated protoplasts, promote cell-to-cell virus movement in the inoculated leaves, facilitate the phloem-dependent long-distance virus spread, and/or intensify disease symptoms in systemically infected tissues. Here we discuss how the various silencing suppression activities of VSRs may facilitate these distinct steps during plant infection and why VSRs may not play a direct role in eliciting disease symptoms by general impairments of host endogenous small RNA pathways. We also highlight many of the key questions still to be addressed on the role of viral suppression of antiviral silencing in plant infection.
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Affiliation(s)
- Juan A Díaz-Pendón
- Center for Plant Cell Biology, Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521, USA.
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