151
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Jouannet V, Moreno AB, Elmayan T, Vaucheret H, Crespi MD, Maizel A. Cytoplasmic Arabidopsis AGO7 accumulates in membrane-associated siRNA bodies and is required for ta-siRNA biogenesis. EMBO J 2012; 31:1704-13. [PMID: 22327216 DOI: 10.1038/emboj.2012.20] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 01/17/2012] [Indexed: 12/13/2022] Open
Abstract
Formation of trans-acting small interfering RNAs (ta-siRNAs) from the TAS3 precursor is triggered by the AGO7/miR390 complex, which primes TAS3 for conversion into double-stranded RNA by the RNA-dependent RNA polymerase RDR6 and SGS3. These ta-siRNAs control several aspects of plant development. The mechanism routing AGO7-cleaved TAS3 precursor to RDR6/SGS3 and its subcellular organization are unknown. We show that AGO7 accumulates together with SGS3 and RDR6 in cytoplasmic siRNA bodies that are distinct from P-bodies. siRNA bodies colocalize with a membrane-associated viral protein and become positive for stress-granule markers upon stress-induced translational repression, this suggests that siRNA bodies are membrane-associated sites of accumulation of mRNA stalled during translation. AGO7 congregates with miR390 and SGS3 in membranes and its targeting to the nucleus prevents its accumulation in siRNA bodies and ta-siRNA formation. AGO7 is therefore required in the cytoplasm and membranous siRNA bodies for TAS3 processing, revealing a hitherto unknown role for membrane-associated ribonucleoparticles in ta-siRNA biogenesis and AGO action in plants.
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Affiliation(s)
- Virginie Jouannet
- Center for Organismal Studies, University of Heidelberg, Heidelberg, Germany
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152
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Jiang J, Laliberté JF. The genome-linked protein VPg of plant viruses-a protein with many partners. Curr Opin Virol 2011; 1:347-54. [PMID: 22440836 DOI: 10.1016/j.coviro.2011.09.010] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Revised: 09/23/2011] [Accepted: 09/26/2011] [Indexed: 12/19/2022]
Abstract
For some plant positive-sense RNA viruses, a protein known as VPg (short for virus protein, genome linked) is covalently linked to the 5' end of the viral RNA. The VPg is an intrinsically disordered protein, and this property would confer an ability to bind several proteins. Accordingly, the potyvirus VPg interacts with many proteins, notably host factors involved in protein synthesis within viral replication factories or within the nucleus. The number of protein partners, the clustering of the various interactions centering around it, the biological importance for some of these interactions (e.g. VPg-eIF4E) and the intrinsically disordered state of the protein are all elements that support the notion that VPg is a hub protein that controls many processes leading to virus production and spread.
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Affiliation(s)
- Jun Jiang
- Institut National de la Recherche Scientifique, Institut Armand-Frappier, 531 Boulevard des Prairies, Laval, Québec, Canada H7V 1B7
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153
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Lerich A, Langhans M, Sturm S, Robinson DG. Is the 6 kDa tobacco etch viral protein a bona fide ERES marker? JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:5013-23. [PMID: 21705387 PMCID: PMC3193009 DOI: 10.1093/jxb/err200] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2011] [Revised: 05/04/2011] [Accepted: 05/26/2011] [Indexed: 05/05/2023]
Abstract
The claim that the 6 kDa viral protein (VP) of Tobacco Etch Virus is a marker for ER exit sites (ERES) has been investigated. When transiently expressed as a CFP tagged fusion construct in tobacco mesophyll protoplasts, this integral membrane protein co-localizes with both the COPII coat protein YFP-SEC24 and the Golgi marker Man1-RFP. However, when over-expressed the VP locates to larger spherical structures which co-localize with neither ER nor Golgi markers. Nevertheless, deletion of the COPII interactive N-terminal D(X)E motif causes it to be broadly distributed throughout the ER, supporting the notion that this protein could be an ERES marker. Curiously, whereas brefeldin A (BFA) caused a typical Golgi-stack response (redistribution into the ER) of the VP in leaf epidermal cells, in protoplasts it resulted in the formation of structures identical to those formed by over-expression. However, anomalous results were obtained with protoplasts: when co-expressed with the non-cycling cis-Golgi marker Man1-RFP, a BFA-induced redistribution of the VP-CFP signal into the ER was observed, but, in the presence of the cycling Golgi marker ERD2-YFP, this did not occur. High resolution images of side-on views of Golgi stacks in epidermal cells showed that the 6 kDa VP-CFP signal overlapped considerably more with YFP-SEC24 than with Man1-RFP, indicating that the VP is proportionately more associated with ERES. However, based on a consideration of the structure of its cytoplasmic tail, the scenario that the VP collects at ERES and is transported to the cis-Golgi before being recycled back to the ER, is supported.
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Affiliation(s)
| | | | | | - David G. Robinson
- Department of Plant Cell Biology, Centre for Organismal Studies, University of Heidelberg, Germany
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154
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Huang TS, Nagy PD. Direct inhibition of tombusvirus plus-strand RNA synthesis by a dominant negative mutant of a host metabolic enzyme, glyceraldehyde-3-phosphate dehydrogenase, in yeast and plants. J Virol 2011; 85:9090-102. [PMID: 21697488 PMCID: PMC3165801 DOI: 10.1128/jvi.00666-11] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Accepted: 06/08/2011] [Indexed: 12/12/2022] Open
Abstract
The replication of plus-strand RNA viruses depends on many cellular factors. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an abundant metabolic enzyme that is recruited to the replicase complex of Tomato bushy stunt virus (TBSV) and affects asymmetric viral RNA synthesis. To further our understanding on the role of GAPDH in TBSV replication, we used an in vitro TBSV replication assay based on recombinant p33 and p92(pol) viral replication proteins and cell-free yeast extract. We found that the addition of purified recombinant GAPDH to the cell extract prepared from GAPDH-depleted yeast results in increased plus-strand RNA synthesis and asymmetric production of viral RNAs. Our data also demonstrate that GAPDH interacts with p92(pol) viral replication protein, which may facilitate the recruitment of GAPDH into the viral replicase complex in the yeast model host. In addition, we have identified a dominant negative mutant of GAPDH, which inhibits RNA synthesis and RNA recruitment in vitro. Moreover, this mutant also exhibits strong suppression of tombusvirus accumulation in yeast and in virus-infected Nicotiana benthamiana. Overall, the obtained data support the model that the co-opted GAPDH plays a direct role in TBSV replication by stimulating plus-strand synthesis by the viral replicase.
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Affiliation(s)
- Tyng-Shyan Huang
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546
| | - Peter D. Nagy
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546
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155
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Schoelz JE, Harries PA, Nelson RS. Intracellular transport of plant viruses: finding the door out of the cell. MOLECULAR PLANT 2011; 4:813-31. [PMID: 21896501 PMCID: PMC3183398 DOI: 10.1093/mp/ssr070] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 07/18/2011] [Indexed: 05/03/2023]
Abstract
Plant viruses are a class of plant pathogens that specialize in movement from cell to cell. As part of their arsenal for infection of plants, every virus encodes a movement protein (MP), a protein dedicated to enlarging the pore size of plasmodesmata (PD) and actively transporting the viral nucleic acid into the adjacent cell. As our knowledge of intercellular transport has increased, it has become apparent that viruses must also use an active mechanism to target the virus from their site of replication within the cell to the PD. Just as viruses are too large to fit through an unmodified plasmodesma, they are also too large to be freely diffused through the cytoplasm of the cell. Evidence has accumulated now for the involvement of other categories of viral proteins in intracellular movement in addition to the MP, including viral proteins originally associated with replication or gene expression. In this review, we will discuss the strategies that viruses use for intracellular movement from the replication site to the PD, in particular focusing on the role of host membranes for intracellular transport and the coordinated interactions between virus proteins within cells that are necessary for successful virus spread.
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Affiliation(s)
- James E. Schoelz
- Division of Plant Sciences, University of Missouri, Columbia, MO 65211, USA
| | - Phillip A. Harries
- Department of Biology, Pittsburg State University, Pittsburg, KS 66762, USA
| | - Richard S. Nelson
- Plant Biology Division, The Samuel Roberts Noble Foundation, Inc., Ardmore, OK 73401, USA
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156
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Martínez F, Sardanyés J, Elena SF, Daròs JA. Dynamics of a plant RNA virus intracellular accumulation: stamping machine vs. geometric replication. Genetics 2011; 188:637-46. [PMID: 21515574 PMCID: PMC3176528 DOI: 10.1534/genetics.111.129114] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2011] [Accepted: 04/16/2011] [Indexed: 01/26/2023] Open
Abstract
The tremendous evolutionary potential of RNA viruses allows them to thrive despite host defense mechanisms and endows them with properties such as emergence, host switching, and virulence. The frequency of mutant viruses after an infectious process results from the interplay between the error rate of the viral replicase, from purifying mechanisms acting after transcription on aberrant RNAs, and from the amplification dynamics of virus RNA positive (+) and negative (-) strands. Two extreme scenarios describing viral RNA amplification are the geometric growth, in which each RNA strand serves as template for the synthesis of complementary strands with the same efficiency, and the stamping machine, where a strand is reiteratively used as template to synthesize multiple copies of the complementary. The resulting mutation frequencies are completely different, being geometric growth largely more mutagenic than stamping machine. In this work we evaluate the contribution of geometric growth and stamping machine to the overall genome amplification of the plant (+)-strand RNA virus turnip mosaic virus (TuMV). By means of transfection experiments of Nicotiana benthamiana protoplasts with a TuMV cDNA infectious clone and by using strand-specific quantitative real-time PCR, we determined the amplification dynamics of viral (+) and (-) RNA during a single-cell infectious process. A mathematical model describing the amplification of each viral strand was fitted to the data. Analyses of the model parameters showed that TuMV (+) and (-) RNA amplification occurs through a mixed strategy with ∼93% of genomes produced via stamping machine and only ∼7% resulting from geometric growth.
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Affiliation(s)
- Fernando Martínez
- Instituto de Biología Molecular y Celular de Plantas (Consejo Superior de Investigaciones Científicas – Universidad Politécnica de Valencia), Valencia, Spain
| | - Josep Sardanyés
- Instituto de Biología Molecular y Celular de Plantas (Consejo Superior de Investigaciones Científicas – Universidad Politécnica de Valencia), Valencia, Spain
| | - Santiago F. Elena
- Instituto de Biología Molecular y Celular de Plantas (Consejo Superior de Investigaciones Científicas – Universidad Politécnica de Valencia), Valencia, Spain
- Santa Fe Institute, Santa Fe, NM 87501, USA
| | - José-Antonio Daròs
- Instituto de Biología Molecular y Celular de Plantas (Consejo Superior de Investigaciones Científicas – Universidad Politécnica de Valencia), Valencia, Spain
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157
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Contribution of topology determinants of a viral movement protein to its membrane association, intracellular traffic, and viral cell-to-cell movement. J Virol 2011; 85:7797-809. [PMID: 21593169 DOI: 10.1128/jvi.02465-10] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The p7B movement protein (MP) of Melon necrotic spot virus (MNSV) is a single-pass membrane protein associated with the endoplasmic reticulum (ER), the Golgi apparatus (GA), and plasmodesmata (Pd). Experimental data presented here revealed that the p7B transmembrane domain (TMD) was sufficient to target the green fluorescent protein (GFP) to ER membranes. In addition, the short extramembrane regions of p7B were essential for subsequent ER export and transport to the GA and Pd. Microsomal partitioning and bimolecular fluorescence assays supported a type II topology of p7B in planta. Mutations affecting conventional determinants of p7B membrane topology, such as the TMD secondary structure, the overall hydrophobicity profile, the so-called "aromatic belt," and the net charge distribution on either side of the TMD, were engineered into infectious RNAs to investigate the relationship between the MP structure and MNSV cell-to-cell movement. The results revealed that (i) the overall hydrophobic profile and the α-helix integrity of the TMD were relevant for virus movement, (ii) modification of the net charge balance of the regions flanking both TMD sides drastically reduced cell-to-cell movement, (iii) localization of p7B to the GA was necessary but not sufficient for virus movement, and (iv) membrane insertion was essential for p7B function in virus movement. Our results therefore indicate that MNSV cell-to-cell movement requires sequential transport of p7B from the ER via the GA to Pd, which is modulated by a combination of several signals with different strengths in the extramembrane regions and TMD of the MP.
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158
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Bamunusinghe D, Seo JK, Rao ALN. Subcellular localization and rearrangement of endoplasmic reticulum by Brome mosaic virus capsid protein. J Virol 2011; 85:2953-63. [PMID: 21209103 PMCID: PMC3067956 DOI: 10.1128/jvi.02020-10] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2010] [Accepted: 12/29/2010] [Indexed: 01/04/2023] Open
Abstract
Genome packaging in the plant-infecting Brome mosaic virus (BMV), a member of the alphavirus-like superfamily, as well as in other positive-strand RNA viruses pathogenic to humans (e.g., poliovirus) and animals (e.g., Flock House virus), is functionally coupled to replication. Although the subcellular localization site of BMV replication has been identified, that of the capsid protein (CP) has remained elusive. In this study, the application of immunofluorescence confocal microscopy to Nicotiana benthamiana leaves expressing replication-derived BMV CP as a green fluorescent protein (GFP) fusion, in conjunction with antibodies to the CP and double-stranded RNA, a presumed marker of RNA replication, revealed that the subcellular localization sites of replication and CP overlap. Our temporal analysis by transmission electron microscopy of ultrastructural modifications induced in BMV-infected N. benthamiana leaves revealed a reticulovesicular network of modified endoplasmic reticulum (ER) incorporating large assemblies of vesicles derived from ER accumulated in the cytoplasm during BMV infection. Additionally, for the first time, we have found by ectopic expression experiments that BMV CP itself has the intrinsic property of modifying ER to induce vesicles similar to those present in BMV infections. The significance of CP-induced vesicles in relation to CP-organized viral functions that are linked to replication-coupled packaging is discussed.
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Affiliation(s)
- Devinka Bamunusinghe
- Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521-0122
| | - Jang-Kyun Seo
- Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521-0122
| | - A. L. N. Rao
- Department of Plant Pathology and Microbiology, University of California, Riverside, California 92521-0122
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159
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Sainsbury F, Sack M, Stadlmann J, Quendler H, Fischer R, Lomonossoff GP. Rapid transient production in plants by replicating and non-replicating vectors yields high quality functional anti-HIV antibody. PLoS One 2010; 5:e13976. [PMID: 21103044 PMCID: PMC2980466 DOI: 10.1371/journal.pone.0013976] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2010] [Accepted: 10/21/2010] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND The capacity of plants and plant cells to produce large amounts of recombinant protein has been well established. Due to advantages in terms of speed and yield, attention has recently turned towards the use of transient expression systems, including viral vectors, to produce proteins of pharmaceutical interest in plants. However, the effects of such high level expression from viral vectors and concomitant effects on host cells may affect the quality of the recombinant product. METHODOLOGY/PRINCIPAL FINDINGS To assess the quality of antibodies transiently expressed to high levels in plants, we have expressed and characterised the human anti-HIV monoclonal antibody, 2G12, using both replicating and non-replicating systems based on deleted versions of Cowpea mosaic virus (CPMV) RNA-2. The highest yield (approximately 100 mg/kg wet weight leaf tissue) of affinity purified 2G12 was obtained when the non-replicating CPMV-HT system was used and the antibody was retained in the endoplasmic reticulum (ER). Glycan analysis by mass-spectrometry showed that the glycosylation pattern was determined exclusively by whether the antibody was retained in the ER and did not depend on whether a replicating or non-replicating system was used. Characterisation of the binding and neutralisation properties of all the purified 2G12 variants from plants showed that these were generally similar to those of the Chinese hamster ovary (CHO) cell-produced 2G12. CONCLUSIONS Overall, the results demonstrate that replicating and non-replicating CPMV-based vectors are able to direct the production of a recombinant IgG similar in activity to the CHO-produced control. Thus, a complex recombinant protein was produced with no apparent effect on its biochemical properties using either high-level expression or viral replication. The speed with which a recombinant pharmaceutical with excellent biochemical characteristics can be produced transiently in plants makes CPMV-based expression vectors an attractive option for biopharmaceutical development and production.
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Affiliation(s)
- Frank Sainsbury
- Department of Biological Chemistry, John Innes Centre, Norwich, United Kingdom.
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