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Jiang C, Shan S, Huang Y, Mao C, Zhang H, Li Y, Chen J, Wei Z, Sun Z. The C-Terminal Transmembrane Domain of Cowpea Mild Mottle Virus TGBp2 Is Critical for Plasmodesmata Localization and for Its Interaction With TGBp1 and TGBp3. Front Microbiol 2022; 13:860695. [PMID: 35495691 PMCID: PMC9051516 DOI: 10.3389/fmicb.2022.860695] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 03/25/2022] [Indexed: 11/13/2022] Open
Abstract
The movement of some plant RNA viruses is mediated by triple gene block (TGB) proteins, which cooperate to transfer the viral genome from cell to cell through plasmodesmata. Here, we investigated the function of the TGB proteins of cowpea mild mottle virus (CPMMV; genus Carlavirus, family Betaflexiviridae), which causes severe damage to soybean production. Subcellular localization experiments demonstrated that TGBp1 and TGBp3 were localized to the endoplasmic reticulum (ER), plasmodesmata (PD) and nucleus in Nicotiana benthamiana leaves. TGBp2 was unusually localized to PD. In protein interaction assays TGBp2 significantly enhanced the interaction between TGBp3 and TGBp1. Interaction assays using deletion mutants showed that the C-terminal transmembrane (TM) domain of TGBp2 is critical for its localization to PD and for its interaction with TGBp1 and TGBp3.
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Meng M, Lee CC. Function and Structural Organization of the Replication Protein of Bamboo mosaic virus. Front Microbiol 2017; 8:522. [PMID: 28400766 PMCID: PMC5368238 DOI: 10.3389/fmicb.2017.00522] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/13/2017] [Indexed: 12/17/2022] Open
Abstract
The genus Potexvirus is one of the eight genera belonging to the family Alphaflexiviridae according to the Virus Taxonomy 2015 released by International Committee on Taxonomy of Viruses (www.ictvonline.org/index.asp). Currently, the genus contains 35 known species including many agricultural important viruses, e.g., Potato virus X (PVX). Members of this genus are characterized by flexuous, filamentous virions of 13 nm in diameter and 470-580 nm in length. A potexvirus has a monopartite positive-strand RNA genome, encoding five open-reading frames (ORFs), with a cap structure at the 5' end and a poly(A) tail at the 3' end. Besides PVX, Bamboo mosaic virus (BaMV) is another potexvirus that has received intensive attention due to the wealth of knowledge on the molecular biology of the virus. In this review, we discuss the enzymatic activities associated with each of the functional domains of the BaMV replication protein, a 155-kDa polypeptide encoded by ORF1. The unique cap formation mechanism, which may be conserved across the alphavirus superfamily, is particularly addressed. The recently identified interactions between the replication protein and the plant host factors are also described.
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Affiliation(s)
- Menghsiao Meng
- Graduate Institute of Biotechnology, National Chung Hsing University Taichung, Taiwan
| | - Cheng-Cheng Lee
- Graduate Institute of Biotechnology, National Chung Hsing University Taichung, Taiwan
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Park MR, Jeong RD, Kim KH. Understanding the intracellular trafficking and intercellular transport of potexviruses in their host plants. FRONTIERS IN PLANT SCIENCE 2014; 5:60. [PMID: 24672528 PMCID: PMC3957223 DOI: 10.3389/fpls.2014.00060] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2013] [Accepted: 02/06/2014] [Indexed: 05/22/2023]
Abstract
The movement of potexviruses through the cytoplasm to plasmodesmata (PD) and through PD to adjacent cells depends on the viral and host cellular proteins. Potexviruses encode three movement proteins [referred to as the triple gene block (TGB1-3)]. TGB1 protein moves cell-to-cell through PD and requires TGB2 and TGB3, which are endoplasmic reticulum (ER)-located proteins. TGB3 protein directs the movement of the ER-derived vesicles induced by TGB2 protein from the perinuclear ER to the cortical ER. TGB2 protein physically interacts with TGB3 protein in a membrane-associated form and also interacts with either coat protein (CP) or TGB1 protein at the ER network. Recent studies indicate that potexvirus movement involves the interaction between TGB proteins and CP with host proteins including membrane rafts. A group of host cellular membrane raft proteins, remorins, can serve as a counteracting membrane platform for viral ribonucleoprotein (RNP) docking and can thereby inhibit viral movement. The CP, which is a component of the RNP movement complex, is also critical for viral cell-to-cell movement through the PD. Interactions between TGB1 protein and/or the CP subunit with the 5'-terminus of genomic RNA [viral RNA (vRNA)] form RNP movement complexes and direct the movement of vRNAs through the PD. Recent studies show that tobacco proteins such as NbMPB2C or NbDnaJ-like proteins interact with the stem-loop 1 RNA located at the 5'-terminus of Potato virus X vRNA and regulate intracellular as well as intercellular movement. Although several host proteins that interact with vRNAs or viral proteins and that are crucial for vRNA transport have been screened and characterized, additional host proteins and details of viral movement remain to be characterized. In this review, we describe recent progress in understanding potexvirus movement within and between cells and how such movement is affected by interactions between vRNA/proteins and host proteins.
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Affiliation(s)
- Mi-Ri Park
- Department of Agricultural Biotechnology, Seoul National UniversitySeoul, South Korea
- Plant Genomics and Breeding Institute, Seoul National UniversitySeoul, South Korea
- Research Institute for Agriculture and Life Sciences, Seoul National UniversitySeoul, South Korea
| | - Rae-Dong Jeong
- Advanced Radiation Technology Institute, Korea Atomic Energy Research InstituteJeongeup, South Korea
| | - Kook-Hyung Kim
- Department of Agricultural Biotechnology, Seoul National UniversitySeoul, South Korea
- Plant Genomics and Breeding Institute, Seoul National UniversitySeoul, South Korea
- Research Institute for Agriculture and Life Sciences, Seoul National UniversitySeoul, South Korea
- *Correspondence: Kook-Hyung Kim, Department of Agricultural Biotechnology, Seoul National University, Seoul 151-921, South Korea e-mail:
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Park MR, Seo JK, Kim KH. Viral and nonviral elements in potexvirus replication and movement and in antiviral responses. Adv Virus Res 2013; 87:75-112. [PMID: 23809921 DOI: 10.1016/b978-0-12-407698-3.00003-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
In Potato virus X, a member of the genus Potexvirus, special sequences and structures at the 5' and 3' ends of the nontranslated region function as cis-acting elements for viral replication. These elements greatly affect interactions between viral RNAs and those between viral RNAs and host factors. The potexvirus genome encodes five open-reading frames. Viral replicase, which is required for the synthesis of viral RNA, binds viral RNA elements and host factors to form a viral replication complex at the host cellular membrane. The coat protein (CP) and three viral movement proteins (TGB1, TGB2, and TGB3) have critical roles in mediating cell-to-cell viral movement through plasmodesmata by virion formation or by nonvirion ribonucleoprotein (RNP) complex formation with viral movement proteins (TGBs). The RNP complex, like TGB1-CP-viral RNA, is associated with viral replicase and used for immediate reinitiation of viral replication in newly invaded cells. Higher plants have defense mechanisms against potexviruses such as Rx-mediated resistance and RNA silencing. The CP acts as an avirulence effector for plant defense mechanisms, while TGB1 functions as a viral suppressor of RNA silencing, which is the mechanism of innate immune resistance. Here, we describe recent findings concerning the involvement of viral and host factors in potexvirus replication and in antiviral responses to potexvirus infection.
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Affiliation(s)
- Mi-Ri Park
- Department of Agricultural Biotechnology, Plant Genomics and Breeding Institute, Seoul National University, Seoul, Republic of Korea
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De La Torre CM, Qu F, Redinbaugh MG, Lewandowski DJ. Biological and molecular characterization of a U.S. isolate of Hosta virus X. PHYTOPATHOLOGY 2012; 102:1176-1181. [PMID: 22809286 DOI: 10.1094/phyto-02-12-0025-r] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Hosta virus X (HVX) is rapidly becoming a serious pathogen of commercially important hosta plants worldwide. We report here biological and molecular characterization of a U.S. isolate of HVX, HVX-37. HVX-37 infectivity was tested in 21 hosta cultivars over three growth seasons, and three types of responses were defined based upon the ability of the virus to cause local and/or systemic infections. Four cultivars resistant to systemic HVX infection were identified. The full-length sequence of the HVX-37 genome was determined, the first complete sequence of a U.S. HVX isolate. Comparison with the previously sequenced HVX-Korea (Kr) genome revealed a high level of sequence similarity, as well as some differences. Notably, a 105-nucleotide long, near-perfect direct repeat in the Kr isolate is absent in HVX-37. The accuracy of the HVX-37 genome sequence was confirmed by infectivity of in vitro transcripts synthesized from a full-length HVX-37 cDNA on Nicotiana benthamiana and hosta plants.
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Komatsu K, Hashimoto M, Maejima K, Shiraishi T, Neriya Y, Miura C, Minato N, Okano Y, Sugawara K, Yamaji Y, Namba S. A necrosis-inducing elicitor domain encoded by both symptomatic and asymptomatic Plantago asiatica mosaic virus isolates, whose expression is modulated by virus replication. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2011; 24:408-20. [PMID: 21190438 DOI: 10.1094/mpmi-12-10-0279] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Systemic necrosis is the most destructive symptom induced by plant pathogens. We previously identified amino acid 1154, in the polymerase domain (POL) of RNA-dependent RNA polymerase (RdRp) of Plantago asiatica mosaic virus (PlAMV), which affects PlAMV-induced systemic necrosis in Nicotiana benthamiana. By point-mutation analysis, we show that amino acid 1,154 alone is not sufficient for induction of necrotic symptoms. However, PlAMV replicons that can express only RdRp, derived from a necrosis-inducing PlAMV isolate, retain their ability to induce necrosis, and transient expression of PlAMV-encoded proteins indicated that the necrosis-eliciting activity resides in RdRp. Moreover, inducible-overexpression analysis demonstrated that the necrosis was induced in an RdRp dose-dependent manner. In addition, during PlAMV infection, necrotic symptoms are associated with high levels of RdRp accumulation. Surprisingly, necrosis-eliciting activity resides in the helicase domain (HEL), not in the amino acid 1,154-containing POL, of RdRp, and this activity was observed even in HELs of PlAMV isolates of which infection does not cause necrosis. Moreover, HEL-induced necrosis had characteristics similar to those induced by PlAMV infection. Overall, our data suggest that necrotic symptoms induced by PlAMV infection depend on the accumulation of a non-isolate specific elicitor HEL (even from nonnecrosis isolates), whose expression is indirectly regulated by amino acid 1,154 that controls replication.
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Affiliation(s)
- Ken Komatsu
- Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan
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Cheng SF, Huang YP, Wu ZR, Hu CC, Hsu YH, Tsai CH. Identification of differentially expressed genes induced by Bamboo mosaic virus infection in Nicotiana benthamiana by cDNA-amplified fragment length polymorphism. BMC PLANT BIOLOGY 2010; 10:286. [PMID: 21184690 PMCID: PMC3024324 DOI: 10.1186/1471-2229-10-286] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Accepted: 12/27/2010] [Indexed: 05/03/2023]
Abstract
BACKGROUND The genes of plants can be up- or down-regulated during viral infection to influence the replication of viruses. Identification of these differentially expressed genes could shed light on the defense systems employed by plants and the mechanisms involved in the adaption of viruses to plant cells. Differential gene expression in Nicotiana benthamiana plants in response to infection with Bamboo mosaic virus (BaMV) was revealed using cDNA-amplified fragment length polymorphism (AFLP). RESULTS Following inoculation with BaMV, N. benthamiana displayed differential gene expression in response to the infection. Isolation, cloning, and sequencing analysis using cDNA-AFLP furnished 90 cDNA fragments with eight pairs of selective primers. Fifteen randomly selected genes were used for a combined virus-induced gene silencing (VIGS) knockdown experiment, using BaMV infection to investigate the roles played by these genes during viral infection, specifically addressing the means by which these genes influence the accumulation of BaMV protein. Nine of the 15 genes showed either a positive or a negative influence on the accumulation of BaMV protein. Six knockdown plants showed an increase in the accumulation of BaMV, suggesting that they played a role in the resistance to viral infection, while three plants showed a reduction in coat protein, indicating a positive influence on the accumulation of BaMV in plants. An interesting observation was that eight of the nine plants showing an increase in BaMV coat protein were associated with cell rescue, defense, death, aging, signal transduction, and energy production. CONCLUSIONS This study reports an efficient and straightforward method for the identification of host genes involved in viral infection. We succeeded in establishing a cDNA-AFLP system to help track changes in gene expression patterns in N. benthamiana plants when infected with BaMV. The combination of both DNA-AFLP and VIGS methodologies made it possible to screen a large number of genes and identify those associated with infections of plant viruses. In this report, 9 of the 15 analyzed genes exhibited either a positive or a negative influence on the accumulation of BaMV in N. benthamiana plants.
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Affiliation(s)
- Shun-Fang Cheng
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Ying-Ping Huang
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Zi-Rong Wu
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Chung-Chi Hu
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
| | - Yau-Heiu Hsu
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
- Graduate Institute of Medical Laboratory Science and Biotechnology, China Medical University, Taichung, 404, Taiwan
| | - Ching-Hsiu Tsai
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, 40227, Taiwan
- Graduate Institute of Medical Laboratory Science and Biotechnology, China Medical University, Taichung, 404, Taiwan
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Verchot-Lubicz J, Torrance L, Solovyev AG, Morozov SY, Jackson AO, Gilmer D. Varied movement strategies employed by triple gene block-encoding viruses. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2010; 23:1231-47. [PMID: 20831404 DOI: 10.1094/mpmi-04-10-0086] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Several RNA virus genera belonging to the Virgaviridae and Flexiviridae families encode proteins organized in a triple gene block (TGB) that facilitate cell-to-cell and long-distance movement. The TGB proteins have been traditionally classified as hordei-like or potex-like based on phylogenetic comparisons and differences in movement mechanisms of the Hordeivirus and Potexvirus spp. However, accumulating data from other model viruses suggests that a revised framework is needed to accommodate the profound differences in protein interactions occurring during infection and ancillary capsid protein requirements for movement. The goal of this article is to highlight common features of the TGB proteins and salient differences in movement properties exhibited by individual viruses encoding these proteins. We discuss common and divergent aspects of the TGB transport machinery, describe putative nucleoprotein movement complexes, highlight recent data on TGB protein interactions and topological properties, and review membrane associations occurring during subcellular targeting and cell-to-cell movement. We conclude that the existing models cannot be used to explain all TGB viruses, and we propose provisional Potexvirus, Hordeivirus, and Pomovirus models. We also suggest areas that might profit from future research on viruses harboring this intriguing arrangement of movement proteins.
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Affiliation(s)
- Jeanmarie Verchot-Lubicz
- Oklahoma State University, Department of Entomology and Plant Pathology, Stillwater, OK 74078, USA.
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RNA 5'-triphosphatase activity of the hepatitis E virus helicase domain. J Virol 2010; 84:9637-41. [PMID: 20592074 DOI: 10.1128/jvi.00492-10] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Hepatitis E virus (HEV) has a positive-sense RNA genome with a 5'-m7G cap. HEV open reading frame 1 (ORF1) encodes a polyprotein with multiple enzyme domains required for replication. HEV helicase is a nucleoside triphosphatase (NTPase) with the ability to unwind RNA duplexes in the 5'-to-3' direction. When incubated with 5'-[gamma-(32)P]RNA and 5'-[alpha-(32)P]RNA, HEV helicase released (32)P only from 5'-[gamma-(32)P]RNA, showing specificity for the gamma-beta-triphosphate bond. Removal of gamma-phosphate from the 5' end of the primary transcripts (pppRNA to ppRNA) by RNA triphosphatase is an essential step during cap formation. It is suggested that HEV employs the helicase to mediate the first step of 5' cap synthesis.
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Draghici HK, Varrelmann M. Evidence that the linker between the methyltransferase and helicase domains of potato virus X replicase is involved in homologous RNA recombination. J Virol 2009; 83:7761-9. [PMID: 19439477 PMCID: PMC2708637 DOI: 10.1128/jvi.00179-08] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Accepted: 05/07/2009] [Indexed: 12/29/2022] Open
Abstract
Recombination in RNA viruses, one of the main factors contributing to their genetic variability and evolution, is a widespread phenomenon. In this study, an in vivo assay to characterize RNA recombination in potato virus X (PVX), under high selection pressure, was established. Agrobacterium tumefaciens was used to express in Nicotiana benthamiana leaf tissue both a PVX isolate labeled with green fluorescent protein (GFP) containing a coat protein deletion mutation (DeltaCP) and a transcript encoding a functional coat protein +3'-ntr. Coexpression of the constructs led to virus movement and systemic infection; reconstituted recombinants were observed in 92% of inoculated plants. Similar results were obtained using particle bombardment, demonstrating that recombination mediated by A. tumefaciens was not responsible for the occurrence of PXC recombinants. The speed of recombination could be estimated by agroinfection of two PVX mutants lacking the 3' and 5' halves of the genome, respectively, with an overlap in the triple gene block 1 gene, allowing GFP expression only in the case of recombination. Ten different pentapeptide insertion scanning replicase mutants with replication abilities comparable to wild-type virus were applied in the different recombination assays. Two neighboring mutants affecting the linker between the methyltransferase and helicase domains were shown to be strongly debilitated in their ability to recombine. The possible functional separation of replication and recombination in the replicase molecule supports the model that RNA recombination represents a distinct function of this protein, although the underlying mechanism still needs to be investigated.
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Affiliation(s)
- Heidrun-Katharina Draghici
- Department of Crop Sciences, Section Plant Virology, University of Göttingen, Grisebachstrasse 6, D-37077 Göttingen, Germany
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Han YT, Hsu YH, Lo CW, Meng M. Identification and functional characterization of regions that can be crosslinked to RNA in the helicase-like domain of BaMV replicase. Virology 2009; 389:34-44. [PMID: 19443005 PMCID: PMC7134557 DOI: 10.1016/j.virol.2009.04.013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2008] [Revised: 04/12/2009] [Accepted: 04/15/2009] [Indexed: 12/27/2022]
Abstract
The helicase-like domain of the Bamboo mosaic virus replicase catalyzes the release of 5'-gamma-phosphate from both ATP and 5'-triphosphated RNA by an identical set of catalytic residues with a presumably larger binding pocket for RNA. In this study, the peptidyl regions involved in RNA binding were mapped by reversible formaldehyde crosslinking and mass spectrometry. Eleven residues within these regions were examined by mutational analysis. H636A, Y704A, and K706A greatly diminished the enzymatic activities and were unable to support the viral replication in Nicotiana benthamiana protoplasts. K843A decreased activity toward the RNA substrate to 17% of WT, and approximately 20% replication efficiency was retained in protoplasts. R597A and K610A retained approximately 50 and approximately 90% of the enzymatic activities, respectively. However, replication in protoplasts of these mutants was extremely limited. Proteins with the mutations K603A, R628A, R645A, H794A, and R799A were present at levels 30-69% of WT in protoplasts. However, the fates of these mutations in plants were different. Viral cell-to-cell movement was limited by the K603A and R628A mutations, while systemic movement was restricted by R645A and H794A. The implications of the helicase-like domain in the viral replication and movement are discussed.
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Affiliation(s)
| | | | | | - Menghsiao Meng
- Graduate Institute of Biotechnology, National Chung Hsing University, 250 Kuo-Kuang Rd, Taichung, Taiwan 40227, ROC
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Cheng CW, Hsiao YY, Wu HC, Chuang CM, Chen JS, Tsai CH, Hsu YH, Wu YC, Lee CC, Meng M. Suppression of bamboo mosaic virus accumulation by a putative methyltransferase in Nicotiana benthamiana. J Virol 2009; 83:5796-805. [PMID: 19297487 PMCID: PMC2681968 DOI: 10.1128/jvi.02471-08] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2008] [Accepted: 03/10/2009] [Indexed: 12/12/2022] Open
Abstract
Bamboo mosaic virus (BaMV) is a 6.4-kb positive-sense RNA virus belonging to the genus Potexvirus of the family Flexiviridae. The 155-kDa viral replicase, the product of ORF1, comprises an N-terminal S-adenosyl-l-methionine (AdoMet)-dependent guanylyltransferase, a nucleoside triphosphatase/RNA 5'-triphosphatase, and a C-terminal RNA-dependent RNA polymerase (RdRp). To search for cellular factors potentially involved in the regulation of replication and/or transcription of BaMV, the viral RdRp domain was targeted as bait to screen against a leaf cDNA library of Nicotiana benthamiana using a yeast two-hybrid system. A putative methyltransferase (PNbMTS1) of 617 amino acid residues without an established physiological function was identified. Cotransfection of N. benthamiana protoplasts with a BaMV infectious clone and the PNbMTS1-expressing plasmid showed a PNbMTS1 dosage-dependent inhibitory effect on the accumulation of BaMV coat protein. Deletion of the N-terminal 36 amino acids, deletion of a predicted signal peptide or transmembrane segment, or mutations in the putative AdoMet-binding motifs of PNbMTS1 abolished the inhibitory effect. In contrast, suppression of PNbMTS1 by virus-induced gene silencing in N. benthamiana increased accumulation of the viral coat protein as well as the viral genomic RNA. Collectively, PNbMTS1 may function as an innate defense protein against the accumulation of BaMV through an uncharacterized mechanism.
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Affiliation(s)
- Chun-Wei Cheng
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
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Draghici HK, Pilot R, Thiel H, Varrelmann M. Functional mapping of PVX RNA-dependent RNA-replicase using pentapeptide scanning mutagenesis-Identification of regions essential for replication and subgenomic RNA amplification. Virus Res 2009; 143:114-24. [PMID: 19463728 DOI: 10.1016/j.virusres.2009.03.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2008] [Revised: 03/23/2009] [Accepted: 03/25/2009] [Indexed: 12/31/2022]
Abstract
The replicase protein of Potato virus X (PVX), type species of the genus Potexvirus, was selected to identify regions essential for replication and subgenomic RNA synthesis. Replicase amino acid (aa) sequence alignment of 16 Potexvirus species resulted in the detection of overall sequence homology of 34.4-65.4%. Two regions of consensus with a high proportion of conserved aa (1-411 and 617-1437 according to PVX) were separated by a hyper-variable linker region. Pentapeptide scanning (PS) mutagenesis in a PVX full-length clone expressing green fluorescent protein (GFP) was carried out. For 69 selected PS-mutants where insertions were spread randomly over the replicase ORF the position of the insertion was determined. The replication activity was evaluated by GFP expression from subgenomic viral RNA of PVX replicase mutants. Only one functional PS-mutant was detected in the N-terminal 430 aa, containing the conserved methyltransferase domain of the protein. In the linker region from aa 430-595, nine mutations were discovered which did not induce significant effects on the replicase replication ability. The part of the protein including helicase and polymerase domains was highly intolerant for the PS insertion as demonstrated by 24 independent more or less uniformly spread mutants.
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Affiliation(s)
- Heidrun-Katharina Draghici
- Department of Crop Sciences, Section Plant Virology, University of Göttingen, Grisebachstrasse 6, D-37077 Göttingen, Germany
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