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Kleinow T, Nischang M, Beck A, Kratzer U, Tanwir F, Preiss W, Kepp G, Jeske H. Three C-terminal phosphorylation sites in the Abutilon mosaic virus movement protein affect symptom development and viral DNA accumulation. Virology 2009; 390:89-101. [PMID: 19464722 DOI: 10.1016/j.virol.2009.04.018] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2009] [Revised: 04/09/2009] [Accepted: 04/23/2009] [Indexed: 01/02/2023]
Abstract
The Abutilon mosaic virus (AbMV, Geminiviridae) DNA B component encodes a movement protein (MP), which facilitates viral transport within plants and affects pathogenicity. The presence of phosphorylated serine and threonine residues was confirmed for MP expressed in yeast and Nicotiana benthamiana by comparative Western blot analysis using phospho-amino acid- and MP-specific immunodetection. Mass spectrometry of yeast-derived MP identified three phosphorylation sites located in the C-terminal domain (Thr-221, Ser-223 and Ser-250). To assess their functional relevance in plants, several point mutations were generated in the MP gene of DNA B, which replace Thr-221, Ser-223 and Ser-250, either singly or in combinations, with either an uncharged alanine or a phosphorylation-mimicking aspartate residue. When co-inoculated with DNA A, all mutants were infectious. In systemically infected plants the symptoms and/or viral DNA accumulation were significantly altered for several of the mutants.
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Affiliation(s)
- Tatjana Kleinow
- Institute of Biology, Department of Molecular Biology and Plant Virology, Universität Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany.
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Shimizu T, Yoshii A, Sakurai K, Hamada K, Yamaji Y, Suzuki M, Namba S, Hibi T. Identification of a novel tobacco DnaJ-like protein that interacts with the movement protein of tobacco mosaic virus. Arch Virol 2009; 154:959-67. [PMID: 19458900 DOI: 10.1007/s00705-009-0397-6] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2008] [Accepted: 04/29/2009] [Indexed: 11/25/2022]
Abstract
The movement protein (MP) of tobacco mosaic virus (TMV) mediates the transport of viral RNA from infected cells to neighboring uninfected cells via plasmodesmata by interacting with putative host factors. To find such host factors, we screened tobacco proteins using the yeast two-hybrid system. NtMPIP1, a novel subset of DnaJ-like proteins, was identified from a tobacco cDNA library, and its specific interaction with TMV MP was confirmed with an in vitro filter-binding assay. In a deletion analysis, using a series of truncated TMV MPs and NtMPIP1s, at least two regions of TMV MP, amino acid residues 65-86 and 120-185, conferred the ability to interact with the C-terminal domain of NtMPIP1, which is thought to be involved in substrate binding. Virus-induced gene silencing of NtMPIP1 significantly inhibited the spread of TMV. Therefore, it is reasonable to consider that endogenous NtMPIP1 is a host factor involved in virus cell-to-cell spread by interacting with TMV MP.
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Affiliation(s)
- Takumi Shimizu
- Laboratory of Plant Pathology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
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53
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Sasaki N, Ogata T, Deguchi M, Nagai S, Tamai A, Meshi T, Kawakami S, Watanabe Y, Matsushita Y, Nyunoya H. Over-expression of putative transcriptional coactivator KELP interferes with Tomato mosaic virus cell-to-cell movement. MOLECULAR PLANT PATHOLOGY 2009; 10:161-73. [PMID: 19236566 PMCID: PMC6640241 DOI: 10.1111/j.1364-3703.2008.00517.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Tomato mosaic virus (ToMV) encodes a movement protein (MP) that is necessary for virus cell-to-cell movement. We have demonstrated previously that KELP, a putative transcriptional coactivator of Arabidopsis thaliana, and its orthologue from Brassica campestris can bind to ToMV MP in vitro. In this study, we examined the effects of the transient over-expression of KELP on ToMV infection and the intracellular localization of MP in Nicotiana benthamiana, an experimental host of the virus. In co-bombardment experiments, the over-expression of KELP inhibited virus cell-to-cell movement. The N-terminal half of KELP (KELPdC), which had been shown to bind to MP, was sufficient for inhibition. Furthermore, the over-expression of KELP and KELPdC, both of which were co-localized with ToMV MP, led to a reduction in the plasmodesmal association of MP. In the absence of MP expression, KELP was localized in the nucleus and the cytoplasm by the localization signal in its N-terminal half. It was also shown that ToMV amplified normally in protoplasts prepared from leaf tissue that expressed KELP transiently. These results indicate that over-expressed KELP interacts with MP in vivo and exerts an inhibitory effect on MP function for virus cell-to-cell movement, but not on virus amplification in individual cells.
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Affiliation(s)
- Nobumitsu Sasaki
- Gene Research Centre, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
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54
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Ben-Nissan G, Cui W, Kim DJ, Yang Y, Yoo BC, Lee JY. Arabidopsis casein kinase 1-like 6 contains a microtubule-binding domain and affects the organization of cortical microtubules,. PLANT PHYSIOLOGY 2008; 4:652-4. [PMID: 18945931 PMCID: PMC2593671 DOI: 10.1104/pp.108.129346] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Accepted: 10/17/2008] [Indexed: 05/18/2023]
Abstract
Members of the casein kinase 1 (CK1) family are evolutionarily conserved eukaryotic protein kinases that are involved in various cellular, physiological, and developmental processes in yeast and metazoans, but the biological roles of CK1 members in plants are not well understood. Here, we report that an Arabidopsis (Arabidopsis thaliana) CK1 member named casein kinase 1-like 6 (CKL6) associates with cortical microtubules in vivo and phosphorylates tubulins in vitro. The unique C-terminal domain of CKL6 was shown to contain the signal that allows localization of CKL6 to the cortical microtubules. This domain on its own was sufficient to associate with microtubules in vivo and to bind tubulins in vitro. CKL6 was able to phosphorylate soluble tubulins as well as microtubule polymers, and its endogenous activity was found to associate with a tubulin-enriched subcellular fraction. Two major in vitro phosphorylation sites were mapped to serine-413 and serine-420 of tubulin beta. Ectopic expression of wild-type CKL6 or a kinase-inactive mutant form induced alterations in cortical microtubule organization and anisotropic cell expansion. Collectively, these results demonstrate that CKL6 is a protein kinase containing a novel tubulin-binding domain and plays a role in anisotropic cell growth and shape formation in Arabidopsis through the regulation of microtubule organization, possibly through the phosphorylation of tubulins.
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Affiliation(s)
- Gili Ben-Nissan
- Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark, Delaware 19711, USA
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55
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Módena NA, Zelada AM, Conte F, Mentaberry A. Phosphorylation of the TGBp1 movement protein of Potato virus X by a Nicotiana tabacum CK2-like activity. Virus Res 2008; 137:16-23. [PMID: 18632176 DOI: 10.1016/j.virusres.2008.04.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2007] [Revised: 03/31/2008] [Accepted: 04/07/2008] [Indexed: 11/19/2022]
Abstract
The movement protein (MP) TGBp1 of the potexvirus Potato virus X (PVX) is a multifunctional protein required for cell-to-cell movement within the host plant. Recent work on other plant viruses has indicated that MP phosphorylation by host kinases can regulate MP function. In this study, we demonstrate that recombinant and native TGBp1 are phosphorylated by Nicotiana tabacum extracts from both PVX-infected and non-infected leaves. The phosphorylation activity present in plant extracts has distinctive characteristics of casein kinase 2 (CK2): it is inhibited by heparin, stimulated by polylysine, and uses either ATP or GTP as phosphoryl donors. We also demonstrate that TGBp1 is efficiently phosphorylated by recombinant tobacco CK2 alpha subunit and by partially purified tobacco CK2. Phosphopeptide mass mapping reveals that TGBp1 is phosphorylated in Ser-165, which is localized within a CK2 consensus sequence. Our results strongly suggest that a N. tabacum kinase of the CK2 family is involved in TBGp1 phosphorylation during the course of viral infection.
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Affiliation(s)
- Natalia Andrea Módena
- Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, CONICET and FCEN-UBA, Buenos Aires, Argentina
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56
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Hwang MS, Kim KN, Lee JH, Park YI. Identification of amino acid sequences determining interaction between the cucumber mosaic virus-encoded 2a polymerase and 3a movement proteins. J Gen Virol 2008; 88:3445-3451. [PMID: 18024915 DOI: 10.1099/vir.0.83207-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The cucumber mosaic virus (CMV)-encoded 3a movement protein (MP) is indispensable for CMV movement in plants. We have previously shown that MP interacts directly with the CMV-encoded 2a polymerase protein in vitro. Here, we further dissected this interaction and determined the amino acid sequences that are responsible for the MP and 2a polymerase protein interaction. Both the N-terminal 21 amino acids and the central GDD motif of the 2a polymerase protein were important for interacting with the MP. Although each of the regions alone was sufficient for the interaction with MP, quantitative yeast two-hybrid analyses showed that they acted synergistically to enhance the binding affinity. The MP N-terminal 20 amino acids were sufficient for interacting with the 2a polymerase protein, and the serine residue at position 14 played a critical role in the interaction. Multiple sequence alignment showed that the 2a protein interacting regions and the serine at position 14 in the MP are highly conserved among subgroup I and II CMV isolates.
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Affiliation(s)
- Min Sook Hwang
- School of Life Sciences and Biotechnology, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Korea
| | - Kyung Nam Kim
- Department of Molecular Biology, Sejong University, Gunja-dong, Gwangjin-gu, Seoul 143-747, Korea
| | - Jeong Hyun Lee
- School of Life Sciences and Biotechnology, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Korea
| | - Young In Park
- School of Life Sciences and Biotechnology, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Korea
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57
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Abstract
Plant viruses encode movement proteins (MPs) which play important roles in spreading their infectious materials throughout host plants. This infection is facilitated by cell-to-cell trafficking of MPs through specialized channels termed plasmodesmata, which involves specific interactions between MPs and host factors. Recently, we have reported the identification of a host protein kinase named plasmodesmal-associated protein kinase (PAPK) which specifically phosphorylates a subset of noncell autonomous proteins in vitro, including MPs of Tobacco mosaic virus (TMV) and Bean dwarf mosaic virus (BDMV). Biochemical purification of PAPK was achieved by developing a method in which a series of liquid chromatographic separations of plasmodesmal-enriched subcellular fractions was coupled with phosphorylation assays using TMV MP as a substrate. Application of this approach may prove useful in isolating other host kinases that interact with various viral components.
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Affiliation(s)
- Jung-Youn Lee
- Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, 15 Innovation Way, Newark, DE 19711, USA
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58
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Abstract
Posttranslational modification of proteins is a key regulatory mechanism in a variety of cellular processes. This chapter outlines the concepts and methods used to investigate protein phosphorylation and its physiological relevance during plant virus infection. Rather than providing an exhaustive review of the experimental protocols for protein phosphorylation analysis, we focus on methods that can be used to study phosphorylation of viral proteins. We address the following points: how to determine that a viral protein of interest is phosphorylated; how to map the phosphorylation sites; how to identify the protein kinase(s) involved. Finally, we describe a number of useful strategies to evaluate the biological significance of phosphorylation.
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Affiliation(s)
- Kristiina M Mäkinen
- Department of Applied Chemistry and Microbiology, University of Helsinki, 27, 00014 Helsinki, Finland
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60
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Abstract
Identification of the roles of replication factors represents one of the major frontiers in current virus research. Among plant viruses, the positive-stranded (+) RNA viruses are the largest group and the most widespread. The central step in the infection cycles of (+) RNA viruses is RNA replication, which leads to rapid production of huge number of viral (+) RNA progeny in the infected plant cells. The RNA replication process is carried out by the virus-specific replicase complex consisting of viral RNA-dependent RNA polymerase, one or more auxiliary viral replication proteins, and host factors, which assemble in specialized membranous compartments in infected cells. Replication is followed by cell-to-cell and long-distance movement to invade the entire plant and/or encapsidation to facilitate transmission to new plants. This chapter provides an overview of our current understanding of the role of viral replication proteins during genome replication. The recent significant progress in this research area is based on development of powerful in vivo and in vitro approaches, including replicase assays, reverse genetic approaches, intracelular localization studies and the use of plant or yeast model hosts.
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Abstract
Plant viruses spread from the initially infected cells to the rest of the plant in several distinct stages. First, the virus (in the form of virions or nucleic acid protein complexes) moves intracellularly from the sites of replication to plasmodesmata (PD, plant-specific intercellular membranous channels), the virus then transverses the PD to spread intercellularly (cell-to-cell movement). Long-distance movement of virus occurs through phloem sieve tubes. The processes of plant virus movement are controlled by specific viral movement proteins (MPs). No extensive sequence similarity has been found in MPs belonging to different plant virus taxonomic groups. Moreover, different MPs were shown to use different pathways and mechanisms for virus transport. Some viral transport systems require a single MP while others require additional virus-encoded proteins to transport viral genomes. In this review, we focus on the functions and properties of different classes of MPs encoded by RNA containing plant viruses.
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62
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Kleinow T, Holeiter G, Nischang M, Stein M, Karayavuz M, Wege C, Jeske H. Post-translational modifications of Abutilon mosaic virus movement protein (BC1) in fission yeast. Virus Res 2007; 131:86-94. [PMID: 17919761 DOI: 10.1016/j.virusres.2007.08.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2007] [Revised: 08/18/2007] [Accepted: 08/23/2007] [Indexed: 02/07/2023]
Abstract
The movement protein (MP) of Abutilon mosaic virus (AbMV, Geminiviridae) exhibited a complex band pattern upon gel electrophoresis indicating its post-translational modification when expressed in AbMV-infected plants or, ectopically, in fission yeasts. High-resolution separation according to charge and molecular weight in acetic acid/urea polyacrylamide or sodium dodecyl sulphate polyacrylamide gels followed by western blot analysis revealed a pattern of AbMV MP from infected plants more related to that from fission yeast than from bacteria. For this reason, expression in fission yeast was established as an experimental system to study post-translational modifications of AbMV MP. Metabolic labelling with 32P-orthophosphate confirmed a phosphorylation of all MP variants suggesting multiple phosphorylation sites. Treatment with calf intestinal alkaline phosphatase removed this label completely, but was unable to eliminate all protein bands with lower electrophoretic mobility. Thus, multiple phosphorylations contribute to the complex migration behaviour of MP, but additional post-translational modifications may occur as well.
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Affiliation(s)
- Tatjana Kleinow
- Institute of Biology, Department of Molecular Biology and Plant Virology, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart, Germany.
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63
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Akamatsu N, Takeda A, Kishimoto M, Kaido M, Okuno T, Mise K. Phosphorylation and interaction of the movement and coat proteins of brome mosaic virus in infected barley protoplasts. Arch Virol 2007; 152:2087-93. [PMID: 17680322 DOI: 10.1007/s00705-007-1038-6] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2007] [Accepted: 06/25/2007] [Indexed: 11/26/2022]
Abstract
The 3a movement protein (B3a) of brome mosaic virus (BMV) plays essential roles in the cell-to-cell movement of BMV. B3a is known to bind nucleic acids, to transport RNA to neighbouring cells, and to form tubular structures. Here, we tested the assumption that phosphorylation may be a mechanism that regulates B3a functions and showed that not only B3a but also the coat protein, BCP, was phosphorylated in BMV-infected barley protoplasts. Both BCP and B3a were detected in a complex immunoprecipitated from BMV-infected protoplasts with anti-B3a antiserum, implying an interaction between BCP and B3a.
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Affiliation(s)
- N Akamatsu
- Laboratory of Plant Pathology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan
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64
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Hofmann C, Sambade A, Heinlein M. Plasmodesmata and intercellular transport of viral RNA. Biochem Soc Trans 2007; 35:142-5. [PMID: 17233621 DOI: 10.1042/bst0350142] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Cell-to-cell communication in plants involves the symplastic trafficking of informational protein and RNA macromolecules through cytoplasmic bridges in the plant cell wall known as plasmodesmata. Viruses exploit this route for the spread of infection and are used as a model to study the mechanisms by which macromolecules are targeted to the pore. Studies using tobacco mosaic virus have led to the identification of host components that participate in plasmodesmal targeting of viral RNA and movement protein.
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Affiliation(s)
- C Hofmann
- Institut de Biologie Moléculaire des Plantes, Laboratoire propre du CNRS (Centre National de la Recherche Scientifique) (UPR 2357) conventionné avec l'Université Louis Pasteur (Strasbourg 1), 12 rue du Général Zimmer, 67084 Strasbourg Cedex, France
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65
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Taoka KI, Ham BK, Xoconostle-Cázares B, Rojas MR, Lucas WJ. Reciprocal phosphorylation and glycosylation recognition motifs control NCAPP1 interaction with pumpkin phloem proteins and their cell-to-cell movement. THE PLANT CELL 2007; 19:1866-84. [PMID: 17601822 PMCID: PMC1955715 DOI: 10.1105/tpc.107.052522] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2007] [Revised: 05/29/2007] [Accepted: 06/04/2007] [Indexed: 05/16/2023]
Abstract
In plants, cell-to-cell trafficking of non-cell-autonomous proteins (NCAPs) involves protein-protein interactions, and a role for posttranslational modification has been implicated. In this study, proteins contained in pumpkin (Cucurbita maxima cv Big Max) phloem sap were used as a source of NCAPs to further explore the molecular basis for selective NCAP trafficking. Protein overlay assays and coimmunoprecipitation experiments established that phosphorylation and glycosylation, on both Nicotiana tabacum NON-CELL-AUTONOMOUS PATHWAY PROTEIN1 (Nt-NCAPP1) and the phloem NCAPs, are essential for their interaction. Detailed molecular analysis of a representative phloem NCAP, Cm-PP16-1, identified the specific residues on which glycosylation and phosphorylation must occur for effective binding to NCAPP1. Microinjection studies confirmed that posttranslational modification on these residues is essential for cell-to-cell movement of Cm-PP16-1. Lastly, a glutathione S-transferase (GST)-Cm-PP16-1 fusion protein system was employed to test whether the peptide region spanning these residues was required for cell-to-cell movement. These studies established that a 36-amino acid peptide was sufficient to impart cell-to-cell movement capacity to GST, a normally cell-autonomous protein. These findings are consistent with the hypothesis that a phosphorylation-glycosylation recognition motif functions to control the binding of a specific subset of phloem NCAPs to NCAPP1 and their subsequent transport through plasmodesmata.
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Affiliation(s)
- Ken-Ichiro Taoka
- Section of Plant Biology, College of Biological Sciences, University of California, Davis, CA 95616, USA
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66
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Curin M, Ojangu EL, Trutnyeva K, Ilau B, Truve E, Waigmann E. MPB2C, a microtubule-associated plant factor, is required for microtubular accumulation of tobacco mosaic virus movement protein in plants. PLANT PHYSIOLOGY 2007; 143:801-11. [PMID: 17189338 PMCID: PMC1803734 DOI: 10.1104/pp.106.091488] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/2006] [Accepted: 11/22/2006] [Indexed: 05/13/2023]
Abstract
Movement protein binding 2C (MPB2C) is a plant endogenous microtubule-associated protein previously identified as an interaction partner of tobacco (Nicotiana tabacum) mosaic virus movement protein (TMV-MP). In this work, the role of MPB2C in cell-to-cell transport of TMV-MP, viral spread of TMV, and subcellular localization of TMV-MP was examined. To this end, plants with reduced MPB2C levels were generated by a gene-silencing strategy. Local and systemic spread of TMV and cell-to-cell movement of TMV-MP were unimpaired in MPB2C-silenced plants as compared to nonsilenced plants, indicating that MPB2C is not required for intercellular transport of TMV-MP itself or spread of TMV. However, a clear change in subcellular distribution of TMV-MP characterized by a nearly complete loss of microtubular localization was observed in MPB2C-silenced plants. This result shows that the MPB2C is a central player in determining the complex subcellular localization of TMV-MP, in particular its microtubular accumulation, a phenomenon that has been frequently observed and whose role is still under discussion. Clearly, MPB2C mediated accumulation of TMV-MP at microtubules is not required for intercellular spread but may be a means to withdraw the TMV-MP from the cell-to-cell transport pathway.
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Affiliation(s)
- Mirela Curin
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Medical Biochemistry, Medical University of Vienna, A-1030 Vienna, Austria
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67
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Wright KM, Wood NT, Roberts AG, Chapman S, Boevink P, Mackenzie KM, Oparka KJ. Targeting of TMV movement protein to plasmodesmata requires the actin/ER network: evidence from FRAP. Traffic 2007; 8:21-31. [PMID: 17132144 DOI: 10.1111/j.1600-0854.2006.00510.x] [Citation(s) in RCA: 125] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fluorescence recovery after photobleaching (FRAP) was used to study the mechanism by which fluorescent-protein-tagged movement protein (MP) of tobacco mosaic virus (TMV) is targeted to plasmodesmata (PD). The data show that fluorescence recovery in PD at the leading edge of an infection requires elements of the cortical actin/endoplasmic reticulum (ER) network and can occur in the absence of an intact microtubule (MT) cytoskeleton. Inhibitors of the actin cytoskeleton (latrunculin and cytochalasin) significantly inhibited MP targeting, while MT inhibitors (colchicine and oryzalin) did not. Application of sodium azide to infected cells implicated an active component of MP transfer to PD. Treatment of cells with Brefeldin A (BFA) at a concentration that caused reabsorption of the Golgi bodies into the ER (precluding secretion of viral MP) had no effect on MP targeting, while disruption of the cortical ER with higher concentrations of BFA caused significant inhibition. Our results support a model of TMV MP function in which targeting of MP to PD during infection is mediated by the actin/ER network.
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Affiliation(s)
- Kathryn M Wright
- Programme of Plant Pathology, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK.
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68
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Culver JN, Padmanabhan MS. Virus-induced disease: altering host physiology one interaction at a time. ANNUAL REVIEW OF PHYTOPATHOLOGY 2007; 45:221-43. [PMID: 17417941 DOI: 10.1146/annurev.phyto.45.062806.094422] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Virus infections are the cause of numerous plant disease syndromes that are generally characterized by the induction of disease symptoms such as developmental abnormalities, chlorosis, and necrosis. How viruses induce these disease symptoms represents a long-standing question in plant pathology. Recent studies indicate that symptoms are derived from specific interactions between virus and host components. Many of these interactions have been found to contribute to the successful completion of the virus life-cycle, although the role of other interactions in the infection process is not yet known. However, all share the potential to disrupt host physiology. From this information we are beginning to decipher the progression of events that lead from specific virus-host interactions to the establishment of disease symptoms. This review highlights our progress in understanding the mechanisms through which virus-host interactions affect host physiology. The emerging picture is one of complexity involving the individual effects of multiple virus-host interactions.
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Affiliation(s)
- James N Culver
- Center for Biosystems Research, University of Maryland Biotechnology Institute, Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742, USA.
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69
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Fujiki M, Kawakami S, Kim RW, Beachy RN. Domains of tobacco mosaic virus movement protein essential for its membrane association. J Gen Virol 2006; 87:2699-2707. [PMID: 16894211 DOI: 10.1099/vir.0.81936-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A series of deletion mutants of tobacco mosaic virus movement protein (TMV-MP) was used to identify domains of the protein necessary for membrane association. A membrane fraction was isolated from tobacco BY-2 protoplasts infected with wild-type and mutant TMV that produce MP carrying a 3 aa deletion. Deletions that affected membrane association were clustered around the two major hydrophobic regions of MP that are predicted to be transmembrane. Deletions in other hydrophobic regions also reduced membrane association. In addition, a non-functional mutant of MP, in which one of the known phosphorylation sites was eliminated, was not associated with cellular membranes, while a functional second site revertant restored membrane association. This indicates that MP function requires interaction with membrane; however, membrane association was not sufficient for function. Results are consistent with the hypothesis that TMV-MP is an integral or tightly associated membrane protein that includes two hydrophobic transmembrane domains.
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Affiliation(s)
- Masaaki Fujiki
- Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA
| | - Shigeki Kawakami
- Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA
| | - Ryan W Kim
- Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA
| | - Roger N Beachy
- Donald Danforth Plant Science Center, 975 North Warson Road, St Louis, MO 63132, USA
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Florentino LH, Santos AA, Fontenelle MR, Pinheiro GL, Zerbini FM, Baracat-Pereira MC, Fontes EPB. A PERK-like receptor kinase interacts with the geminivirus nuclear shuttle protein and potentiates viral infection. J Virol 2006; 80:6648-56. [PMID: 16775352 PMCID: PMC1488943 DOI: 10.1128/jvi.00173-06] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The nuclear shuttle protein (NSP) from bipartite geminiviruses facilitates the intracellular transport of viral DNA from the nucleus to the cytoplasm and acts in concert with the movement protein (MP) to promote the cell-to-cell spread of the viral DNA. A proline-rich extensin-like receptor protein kinase (PERK) was found to interact specifically with NSP of Cabbage leaf curl virus (CaLCuV) and of tomato-infecting geminiviruses through a yeast two-hybrid screening. The PERK-like protein, which we designated NsAK (for NSP-associated kinase), is structurally organized into a proline-rich N-terminal domain, followed by a transmembrane segment and a C-terminal serine/threonine kinase domain. The viral protein interacted stably with defective versions of the NsAK kinase domain, but not with the potentially active enzyme, in an in vitro binding assay. In vitro-translated NsAK enhanced the phosphorylation level of NSP, indicating that NSP functions as a substrate for NsAK. These results demonstrate that NsAK is an authentic serine/threonine kinase and suggest a functional link for NSP-NsAK complex formation. This interpretation was corroborated by in vivo infectivity assays showing that loss of NsAK function reduces the efficiency of CaLCuV infection and attenuates symptom development. Our data implicate NsAK as a positive contributor to geminivirus infection and suggest it may regulate NSP function.
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Affiliation(s)
- Lilian H Florentino
- Departamento de Bioquímica e Biologia Molecular/BIOAGRO, Universidade Federal de Viçosa, 36571.000 Viçosa, MG, Brazil
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71
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Tyulkina LG, Skurat EV, Zvereva AS, Dorokhov YL, Atabekov JG. Movement protein stimulates tobacco mosaic virus reproduction in infected cells. DOKL BIOCHEM BIOPHYS 2006; 409:253-6. [PMID: 16986444 DOI: 10.1134/s1607672906040168] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Affiliation(s)
- L G Tyulkina
- Faculty of Biology, Moscow State University, Vorob'evy gory, Moscow 119992, Russia
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72
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Seemanpillai M, Elamawi R, Ritzenthaler C, Heinlein M. Challenging the role of microtubules in Tobacco mosaic virus movement by drug treatments is disputable. J Virol 2006; 80:6712-5. [PMID: 16775361 PMCID: PMC1488984 DOI: 10.1128/jvi.00453-06] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2006] [Accepted: 04/10/2006] [Indexed: 11/20/2022] Open
Abstract
The movement protein (MP) of Tobacco mosaic virus interacts with microtubules during infection. Although this interaction is correlated with the function of MP in the cell-to-cell transport of viral RNA, a direct role of microtubules in the movement process was recently challenged by studies involving the treatment of plants with inhibitors of microtubule polymerization. Here, we report evidence suggesting that such treatments may not efficiently disrupt all microtubules. Thus, results obtained from studies using microtubule inhibitors may have to remain open to interpretation with regard to the involvement of microtubules in viral RNA trafficking.
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Affiliation(s)
- Mark Seemanpillai
- Institut Biologie Moléculaire des Plantes, 12 Rue du Général Zimmer, 67084 Strasbourg Cedex, France
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73
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Sasaki N, Park JW, Maule AJ, Nelson RS. The cysteine–histidine-rich region of the movement protein of Cucumber mosaic virus contributes to plasmodesmal targeting, zinc binding and pathogenesis. Virology 2006; 349:396-408. [PMID: 16603215 DOI: 10.1016/j.virol.2006.02.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2005] [Revised: 12/13/2005] [Accepted: 02/15/2006] [Indexed: 11/18/2022]
Abstract
Viral movement proteins (MPs) are central to the establishment of viral pathogenesis, and yet relatively little is understood about the structural and functional aspects of MPs or about the host factors on which they depend. Through chemical mutagenesis of transgenic Arabidopsis expressing Cucumber mosaic virus (CMV) MP fused with the green fluorescent protein, we have studied the function of a central region of the MP, defined by a number of conserved cysteine and histidine residues (Cys-His-rich region), which potentially functions as a zinc-binding domain. Transient expression of mutant MPs identified through an in planta screen for altered MP function or constructed with altered putative zinc ligands through site-directed mutagenesis showed that mutations in the Cys-His-rich region affected localization to and trafficking through plasmodesmata. In vitro zinc-binding analysis revealed that wild type (wt) CMV MP had the ability to bind zinc and that movement-defective mutants bound zinc with less affinity than wt MP. Furthermore, a correlation between the association of the MP with plasmodesmata and virus pathogenesis was shown. We discuss roles of the Cys-His region in biochemical and biological functions of the MP during virus movement.
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Affiliation(s)
- Nobumitsu Sasaki
- Plant Biology Division, The Samuel Roberts Noble Foundation, Inc., 2510 Sam Noble Parkway, Ardmore, OK 73402, USA
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74
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Jakubiec A, Tournier V, Drugeon G, Pflieger S, Camborde L, Vinh J, Héricourt F, Redeker V, Jupin I. Phosphorylation of viral RNA-dependent RNA polymerase and its role in replication of a plus-strand RNA virus. J Biol Chem 2006; 281:21236-21249. [PMID: 16717096 DOI: 10.1074/jbc.m600052200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Central to the process of plus-strand RNA virus genome amplification is the viral RNA-dependent RNA polymerase (RdRp). Understanding its regulation is of great importance given its essential function in viral replication and the common architecture and catalytic mechanism of polymerases. Here we show that Turnip yellow mosaic virus (TYMV) RdRp is phosphorylated, when expressed both individually and in the context of viral infection. Using a comprehensive biochemical approach, including metabolic labeling and mass spectrometry analyses, phosphorylation sites were mapped within an N-terminal PEST sequence and within the highly conserved palm subdomain of RNA polymerases. Systematic mutational analysis of the corresponding residues in a reverse genetic system demonstrated their importance for TYMV infectivity. Upon mutation of the phosphorylation sites, distinct steps of the viral cycle appeared affected, but in contrast to other plus-strand RNA viruses, the interaction between viral replication proteins was unaltered. Our results also highlighted the role of another TYMV-encoded replication protein as an antagonistic protein that may prevent the inhibitory effect of RdRp phosphorylation on viral infectivity. Based on these data, we propose that phosphorylation-dependent regulatory mechanisms are essential for viral RdRp function and virus replication.
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Affiliation(s)
| | | | | | | | | | - Joëlle Vinh
- Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris, 75005 Paris, France
| | | | - Virginie Redeker
- Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris, 75005 Paris, France
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75
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Lucas WJ. Plant viral movement proteins: Agents for cell-to-cell trafficking of viral genomes. Virology 2006; 344:169-84. [PMID: 16364748 DOI: 10.1016/j.virol.2005.09.026] [Citation(s) in RCA: 317] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Accepted: 09/10/2005] [Indexed: 10/25/2022]
Abstract
Plants viruses spread throughout their hosts using a number of pathways, the most common being movement cell to cell through plasmodesmata (PD), unique intercellular organelles of the plant kingdom, and between organs by means of the vascular system. Pioneering studies on plant viruses revealed that PD allow the cell-to-cell trafficking of virally encoded proteins, termed the movement proteins (MPs). This non-cell-autonomous protein (NCAP) pathway is similarly employed by the host to traffic macromolecules. Viral MPs bind RNA/DNA in a sequence nonspecific manner to form nucleoprotein complexes (NPC). Host proteins are then involved in the delivery of MPs and NPC to the PD orifice, and a role for the cytoskeleton has been implicated. Trafficking of NCAPs through the PD structure involves three steps in which the MP: (a) interacts with a putative PD docking complex, (b) induces dilation in the PD microchannels, and (c) binds to an internal translocation system for delivery into the neighboring cytoplasm. Viral genera that use this NCAP pathway have evolved a combination of a MP and ancillary proteins that work in concert to enable the formation of a stable NPC that can compete with endogenous NCAPs for the PD trafficking machinery. Incompatible MP-host protein interactions may underlie observed tissue tropisms and restricted infection domains. These pivotal discoveries are discussed in terms of the need to develop a more comprehensive understanding of the (a) three-dimensional structure of MPs, (b) PD supramolecular complex, and (c) host proteins involved in this cell-to-cell trafficking process.
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Affiliation(s)
- William J Lucas
- Section of Plant Biology, College of Biological Sciences, University of California, One Shields Ave., Davis, CA 95616, USA.
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76
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Aronsson H, Combe J, Patel R, Jarvis P. In vivo assessment of the significance of phosphorylation of theArabidopsischloroplast protein import receptor, atToc33. FEBS Lett 2005; 580:649-55. [PMID: 16412428 DOI: 10.1016/j.febslet.2005.12.055] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2005] [Revised: 12/15/2005] [Accepted: 12/15/2005] [Indexed: 11/18/2022]
Abstract
atToc33 is a transit peptide receptor of the chloroplast outer envelope membrane, and possesses GTPase activity. In vitro, its transit peptide- and GTP-binding properties are abrogated by its phosphorylation at serine 181, which was proposed to represent an important regulatory mechanism. We mutated S181 to alanine (to prevent phosphorylation), and to aspartate and glutamate (to mimic the effects of phosphoserine), and expressed all three proteins in ppi1 (atToc33 knockout) plants using the native promoter. The mutants complemented ppi1 with equal efficiency in respect of all criteria tested, including protein import efficiency and light stress tolerance. The data suggest that atToc33 phosphorylation may not play an important role in vivo.
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Affiliation(s)
- Henrik Aronsson
- Department of Plant and Environmental Sciences, Göteborg University, Box 461, SE-405 30 Göteborg, Sweden
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77
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Shapka N, Stork J, Nagy PD. Phosphorylation of the p33 replication protein of Cucumber necrosis tombusvirus adjacent to the RNA binding site affects viral RNA replication. Virology 2005; 343:65-78. [PMID: 16154610 DOI: 10.1016/j.virol.2005.08.006] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/10/2005] [Accepted: 08/08/2005] [Indexed: 11/24/2022]
Abstract
Replication of the nonsegmented, plus-stranded RNA genome of Cucumber necrosis tombusvirus (CNV) requires two essential overlapping viral-coded replication proteins, the p33 replication co-factor and the p92 RNA-dependent RNA polymerase. In this paper, we demonstrate that p33 is phosphorylated in vivo and in vitro by a membrane-bound plant kinase. Phosphorylation of p33 was also demonstrated in vitro by using purified protein kinase C. The related p28 replication protein of Turnip crinkle virus was also found to be phosphorylated in vivo, suggesting that posttranslational modification of replication proteins is a general feature among members of the large Tombusviridae family. Based on in vitro studies with purified recombinant p33, we show evidence for phosphorylation of threonine and serine residues adjacent to the essential RNA-binding site in p33. Phosphorylation-mimicking aspartic acid mutations rendered p33 nonfunctional in plant protoplasts and in yeast, a model host. Comparable mutations within the prereadthrough portion of p92 did not abolish replication. The nonphosphorylation-mimicking alanine mutants of CNV were able to replicate in plant protoplasts and in yeast, albeit with reduced efficiency when compared to the wild type. These alanine mutants also showed altered subgenomic RNA synthesis and a reduction in the ratio between plus- and minus-strand RNAs produced during CNV infection. These findings suggest that phosphorylation of threonine/serine residues adjacent to the essential RNA-binding site in the auxiliary p33 protein likely plays a role in viral RNA replication and subgenomic RNA synthesis during tombusvirus infections.
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Affiliation(s)
- Natalia Shapka
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, KY 40546, USA
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78
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Sanfaçon H. Replication of positive-strand RNA viruses in plants: contact points between plant and virus components. ACTA ACUST UNITED AC 2005. [DOI: 10.1139/b05-121] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Positive-strand RNA viruses constitute the largest group of plant viruses and have an important impact on world agriculture. These viruses have small genomes that encode a limited number of proteins and depend on their hosts to complete the various steps of their replication cycle. In this review, the contact points between positive-strand RNA plant viruses and their hosts, which are necessary for the translation and replication of the viral genomes, are discussed. Special emphasis is placed on the description of viral replication complexes that are associated with specific membranous compartments derived from plant intracellular membranes and contain viral RNAs and proteins as well as a variety of host proteins. These complexes are assembled via an intricate network of protein–protein, protein–membrane, and protein–RNA interactions. The role of host factors in regulating the assembly, stability, and activity of viral replication complexes are also discussed.
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Affiliation(s)
- Hélène Sanfaçon
- Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, 4200 Highway 97, Summerland, BC V0H 1Z0, Canada (e-mail: )
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79
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Lee JY, Taoka KI, Yoo BC, Ben-Nissan G, Kim DJ, Lucas WJ. Plasmodesmal-associated protein kinase in tobacco and Arabidopsis recognizes a subset of non-cell-autonomous proteins. THE PLANT CELL 2005; 17:2817-31. [PMID: 16126836 PMCID: PMC1242275 DOI: 10.1105/tpc.105.034330] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2005] [Revised: 07/22/2005] [Accepted: 08/04/2005] [Indexed: 05/04/2023]
Abstract
Cell-to-cell communication in plants involves the trafficking of macromolecules through specialized intercellular organelles, termed plasmodesmata. This exchange of proteins and RNA is likely regulated, and a role for protein phosphorylation has been implicated, but specific components remain to be identified. Here, we describe the molecular characterization of a plasmodesmal-associated protein kinase (PAPK). A 34-kD protein, isolated from a plasmodesmal preparation, exhibits calcium-independent kinase activity and displays substrate specificity in that it recognizes a subset of viral and endogenous non-cell-autonomous proteins. This PAPK specifically phosphorylates the C-terminal residues of tobacco mosaic virus movement protein (TMV MP); this posttranslational modification has been shown to affect MP function. Molecular analysis of purified protein established that tobacco (Nicotiana tabacum) PAPK is a member of the casein kinase I family. Subcellular localization studies identified a possible Arabidopsis thaliana PAPK homolog, PAPK1. TMV MP and PAPK1 are colocalized within cross-walls in a pattern consistent with targeting to plasmodesmata. Moreover, Arabidopsis PAPK1 also phosphorylates TMV MP in vitro at its C terminus. These results strongly suggest that Arabidopsis PAPK1 is a close homolog of tobacco PAPK. Thus, PAPK1 represents a novel plant protein kinase that is targeted to plasmodesmata and may play a regulatory role in macromolecular trafficking between plant cells.
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Affiliation(s)
- Jung-Youn Lee
- Section of Plant Biology, Division of Biological Sciences, University of California, Davis, CA 95616, USA.
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80
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Stork J, Panaviene Z, Nagy PD. Inhibition of in vitro RNA binding and replicase activity by phosphorylation of the p33 replication protein of Cucumber necrosis tombusvirus. Virology 2005; 343:79-92. [PMID: 16154612 DOI: 10.1016/j.virol.2005.08.005] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 06/10/2005] [Accepted: 08/08/2005] [Indexed: 10/25/2022]
Abstract
Tombusviruses, which are small plus-strand RNA viruses of plants, require the viral-coded p33 replication co-factor for template selection and recruitment into replication in infected cells. As presented in the accompanying paper [Shapka, N., Stork, J., Nagy, P.D., 2005. Phosphorylation of the p33 replication protein of Cucumber necrosis tombusvirus adjacent to the RNA binding site affects viral RNA replication. J. Virol. 343, 65-78.], p33 can be phosphorylated in vitro at serine and threonine residues adjacent to its arginine-proline-rich RNA binding site. To test the effect of phosphorylation on p33 function, in this paper, we used phosphorylation-mimicking aspartic acid mutants of Cucumber necrosis virus (CNV) p33 and in-vitro-phosphorylated p33 in gel mobility shift experiments. We found that phosphorylation inhibited the ability of p33 to bind to the viral RNA. In contrast, the nonphosphorylation-mimicking alanine mutants of p33 bound to viral RNA as efficiently as the nonphosphorylated wild type p33 did. In vitro assays with purified CNV replicase preparations revealed that phosphorylation-mimicking mutants of p33 did not support the assembly of functional CNV replicase complexes in yeast, a model host. Based on these results, we propose that the primary function of reversible phosphorylation of p33 is to regulate the RNA binding capacity of p33, which could affect the assembly of new viral replicase complexes, recruitment of the viral RNA template into replication and/or release of viral RNA from replication. Thus, phosphorylation of p33 might help in switching the role of the viral RNA from replication to other processes, such as viral RNA encapsidation and cell-to-cell movement in infected hosts.
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Affiliation(s)
- Jozsef Stork
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, Lexington, KY 40546, USA
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81
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Rinne PLH, van den Boogaard R, Mensink MGJ, Kopperud C, Kormelink R, Goldbach R, van der Schoot C. Tobacco plants respond to the constitutive expression of the tospovirus movement protein NS(M) with a heat-reversible sealing of plasmodesmata that impairs development. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2005; 43:688-707. [PMID: 16115066 DOI: 10.1111/j.1365-313x.2005.02489.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Viral infection often results in typical symptoms, the biological background of which has remained elusive. We show that constitutive expression of the NSM viral movement protein (MP) of tomato spotted wilt virus in Nicotiana tabacum is sufficient to induce severe, infection-like symptoms, including pronounced deficiencies in root and shoot development. Leaves failed to expand and were arranged in a rosette due to the absence of internode elongation. Following the sink-source transition they accumulated excessive amounts of starch and developed fusing chlorotic patches in the mesophyll, resembling virus-induced chlorotic lesions. Eventually, the leaves became entirely white and brittle. With a combination of techniques, including photosystem II quantum-yield measurements, iontophoresis of symplasmic tracers, bombardment with pPVX.GFP and double immunolabelling it was shown that these symptoms correlated with the obstruction of NSM-targeted mesophyll plasmodesmata (Pd) in source tissues by depositions of 1,3-beta-D-glucan (GLU) or callose. Temperature-shift treatments (TST; 22-->32 degrees C), known to abolish chlorotic local lesions, also abolished the chlorotic 'superlesions' of transgenic plants and rescued plant development, by restoring the transport capacity of Pd through the action of 1,3-beta-D-glucanase (GLU-h) or callase. Return of these elongated, TST-recovered plants to 22 degrees C reintroduced superlesions and arrested shoot elongation, resulting in the formation of a rosette of clustered leaves at the shoot tip. Collectively, this indicates that the symptoms of NSM plants are self-inflicted and due to a basal defence response that counteracts prolonged interference of the MP with Pd functioning. This type of defence may also play a role in the formation of symptoms during viral infection.
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Affiliation(s)
- Päivi L H Rinne
- Laboratory of Virology, Wageningen University, Binnenhaven 11, 6709 PD Wageningen, The Netherlands
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82
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Chen MH, Tian GW, Gafni Y, Citovsky V. Effects of calreticulin on viral cell-to-cell movement. PLANT PHYSIOLOGY 2005; 138:1866-76. [PMID: 16006596 PMCID: PMC1183378 DOI: 10.1104/pp.105.064386] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2005] [Revised: 05/12/2005] [Accepted: 05/23/2005] [Indexed: 05/03/2023]
Abstract
Cell-to-cell tobacco mosaic virus movement protein (TMV MP) mediates viral spread between the host cells through plasmodesmata. Although several host factors have been shown to interact with TMV MP, none of them coresides with TMV MP within plasmodesmata. We used affinity purification to isolate a tobacco protein that binds TMV MP and identified it as calreticulin. The interaction between TMV MP and calreticulin was confirmed in vivo and in vitro, and both proteins were shown to share a similar pattern of subcellular localization to plasmodesmata. Elevation of the intracellular levels of calreticulin severely interfered with plasmodesmal targeting of TMV MP, which, instead, was redirected to the microtubular network. Furthermore, in TMV-infected plant tissues overexpressing calreticulin, the inability of TMV MP to reach plasmodesmata substantially impaired cell-to-cell movement of the virus. Collectively, these observations suggest a functional relationship between calreticulin, TMV MP, and viral cell-to-cell movement.
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Affiliation(s)
- Min-Huei Chen
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York 11794-5215, USA
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83
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Boevink P, Oparka KJ. Virus-host interactions during movement processes. PLANT PHYSIOLOGY 2005; 138:1815-21. [PMID: 16172094 PMCID: PMC1183373 DOI: 10.1104/pp.105.066761] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Affiliation(s)
- Petra Boevink
- Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom
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84
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Nelson RS, Citovsky V. Plant viruses. Invaders of cells and pirates of cellular pathways. PLANT PHYSIOLOGY 2005; 138:1809-14. [PMID: 16172093 PMCID: PMC1183372 DOI: 10.1104/pp.104.900167] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
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85
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Tremblay D, Vaewhongs AA, Turner KA, Sit TL, Lommel SA. Cell wall localization of Red clover necrotic mosaic virus movement protein is required for cell-to-cell movement. Virology 2005; 333:10-21. [PMID: 15708588 DOI: 10.1016/j.virol.2004.12.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2004] [Revised: 08/31/2004] [Accepted: 12/10/2004] [Indexed: 11/22/2022]
Abstract
The Red clover necrotic mosaic virus movement protein (MP) is essential for cell-to-cell movement. Eight previously characterized alanine-scanning mutants of the MP were fused to the green fluorescent protein (GFP) and expressed from viral infectious transcripts. Inoculated plants were assayed for movement and intracellular accumulation of MP by confocal laser-scanning microscopy. A strict correlation was observed between the targeting to the cell wall (presumably the plasmodesmata) and cell-to-cell movement. Complementation of dysfunctional MP mutants with either wild-type MP or other null mutants in some cases rescued intracellular targeting and movement. The data suggest the presence of distinct domains in the MP for virus movement (near residues 27-31), complementarity (near residues 122 and 128), and intracellular localization (near residue 161). These data support a model of MP interacting cooperatively with itself to bind viral RNA, localize to and modify plasmodesmata and effect virus movement.
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Affiliation(s)
- Douglas Tremblay
- Department of Plant Pathology, Box 7616 North Carolina State University, Raleigh NC, 27695-7616 USA
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86
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Trutnyeva K, Bachmaier R, Waigmann E. Mimicking carboxyterminal phosphorylation differentially effects subcellular distribution and cell-to-cell movement of Tobacco mosaic virus movement protein. Virology 2005; 332:563-77. [PMID: 15680421 DOI: 10.1016/j.virol.2004.11.040] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2004] [Revised: 10/28/2004] [Accepted: 11/22/2004] [Indexed: 11/28/2022]
Abstract
Phosphorylation of Tobacco mosaic virus movement protein (TMV-MP) at three carboxyterminal Ser/Thr sites negatively regulates TMV-MP gating function and viral spread in Nicotiana tabacum but not in Nicotiana benthamiana, indicating a host dependant inactivation strategy. Here, we examine the effect of mimicking carboxyterminal phosphorylation on cell-to-cell transport of TMV-MP protein itself in host plants Nicotiana clevelandii, N. benthamiana, Nicotiana glutinosa and N. tabacum. Since TMV-MP transport function was inactivated only in N. tabacum, this host was chosen to explore the contribution of individual carboxyterminal phosphorylation sites. Selective mimicking of phosphorylation at one site enhances TMV-MP cell-to-cell transport, whereas a negative effect requires mimicking of phosphorylation at two or three sites. Potentially, during viral infection in N. tabacum, MP phosphorylation may occur sequentially: first, MP phosphorylation at a single site might ensure effective viral movement; only thereafter, further phosphorylation events may lead to inactivation of TMV-MP transport function.
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Affiliation(s)
- Kateryna Trutnyeva
- Max F. Perutz Laboratories, Department of Medical Biochemistry, University Departments at the Vienna Biocenter, Medical University of Vienna, Dr. Bohrgasse 9, A-1030 Vienna, Austria
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87
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Kim JY. Regulation of short-distance transport of RNA and protein. CURRENT OPINION IN PLANT BIOLOGY 2005; 8:45-52. [PMID: 16207533 DOI: 10.1016/j.pbi.2004.11.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The intercellular trafficking of proteins and RNAs has emerged as a novel mechanism of cell-cell communication in plant development. Plasmodesmata (PD), intercellular cytoplasmic channels, have a central role in cell-cell trafficking of regulatory proteins and RNAs. Recent studies have demonstrated that plants use either a selective or a non-selective PD trafficking pathway for regulatory proteins. Moreover, plants have developed strategies to regulate both selective and non-selective movement. Recent work has focused especially on integrating the recent understanding of the function and mechanisms of intercellular macromolecule movement through PD.
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Affiliation(s)
- Jae-Yean Kim
- Division of Applied Life Science, Plant Molecular Biology and Biotechnology Research Center, Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju 660-701, Korea.
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88
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Gallagher KL, Benfey PN. Not just another hole in the wall: understanding intercellular protein trafficking. Genes Dev 2005; 19:189-95. [PMID: 15655108 DOI: 10.1101/gad.1271005] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Development and differentiation of multicellular organisms requires cell-to-cell communication. In plants direct signaling and exchange of macromolecules between cells is possible through plasmodesmata. Recently direct exchange of membrane-bound vesicles and organelles has been demonstrated between animal cells through formation of cytoplasmic bridges (tunneling nanotubes) in vitro. Here we review recent developments in cell-to-cell trafficking of macromolecules in plants and animals.
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89
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Ryang BS, Kobori T, Matsumoto T, Kosaka Y, Ohki ST. Cucumber mosaic virus 2b protein compensates for restricted systemic spread of Potato virus Y in doubly infected tobacco. J Gen Virol 2004; 85:3405-3414. [PMID: 15483258 DOI: 10.1099/vir.0.80176-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Tobacco plants (Nicotiana tabacum cv. Xanthi-nc) inoculated with a necrotic strain of Potato virus Y (PVY, T01 isolate) developed necrotic symptoms in some systemically infected leaves, but not in younger leaves. However, PVY expressed distinct symptoms not only in the older leaves, but also in the younger leaves, of plants that had been doubly inoculated with PVY and with Cucumber mosaic virus (CMV, strain Pepo). A tissue blot immunoassay of tissues from various positions of the stem detected PVY weakly in each stem, but not in the shoot apex, of singly infected plants, whereas PVY was detected at high levels in almost all sections of doubly infected plants. CMV was also detected at high levels in sections of singly and doubly infected plants. Immunohistochemistry of stem tissues showed that in singly infected plants, PVY was confined to external phloem cells and was not detected in internal phloem cells. However, in doubly infected plants, PVY was distributed uniformly throughout whole tissues, including the external phloem, xylem parenchyma and internal phloem cells. In plants that were doubly infected with PVY and Pepo Delta 2b, a modified CMV that cannot translate the 2b protein, the spread of PVY was restricted as in singly infected plants. These results suggested that the plant host has a counterdefence mechanism that restricts systemic spread of PVY T01, and that the 2b protein of CMV strain Pepo negates this restriction.
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Affiliation(s)
- Bo-Song Ryang
- Kyoto Prefectural Institute of Agricultural Biotechnology, Seika-cho, Soraku-gun, Kyoto 619-0244, Japan
- Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka 599-8531, Japan
| | - Takashi Kobori
- Kyoto Prefectural Institute of Agricultural Biotechnology, Seika-cho, Soraku-gun, Kyoto 619-0244, Japan
| | - Tadashi Matsumoto
- Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka 599-8531, Japan
| | - Yoshitaka Kosaka
- Kyoto Prefectural Institute of Agricultural Biotechnology, Seika-cho, Soraku-gun, Kyoto 619-0244, Japan
| | - Satoshi T Ohki
- Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, Gakuen-cho, Sakai, Osaka 599-8531, Japan
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90
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Abstract
The evolution of intercellular communication had an important role in the increasing complexity of both multicellular and supracellular organisms. Plasmodesmata, the intercellular organelles of the plant kingdom, establish an effective pathway for local and long-distance signalling. In higher plants, this pathway involves the trafficking of proteins and various forms of RNA that function non-cell-autonomously to affect developmental programmes.
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Affiliation(s)
- William J Lucas
- Department of Plant Biology, University of California, Davis, California 95616, USA.
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91
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Sena G, Jung JW, Benfey PN. A broad competence to respond to SHORT ROOT revealed by tissue-specific ectopic expression. Development 2004; 131:2817-26. [PMID: 15142972 DOI: 10.1242/dev.01144] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In plants, cell fate specification depends primarily on position rather than lineage. Recent results indicate that positional information can be transmitted through intercellular trafficking of transcription factors. The SHORT ROOT (SHR) gene, a member of the GRAS family of putative transcription factors, is involved in root radial patterning in Arabidopsis. Correct radial patterning depends on the positional information transmitted through limited SHR intercellular movement and translated into cell division and specification by competent target cells. To investigate the regulation of SHR movement and the competence to respond to it, we drove expression of a translational fusion SHR::GFP using four different tissue-specific promoters. In a wild-type background, SHR::GFP was not able to move from either phloem companion cells or epidermal cells, both of which have been shown to support movement of other proteins, suggesting a requirement for tissue-specific factors for SHR movement. When expressed from its native promoter in plants with multiple endodermal layers, SHR::GFP was not able to move beyond the first endodermal layer, indicating that movement is not limited by a mechanism that recognizes boundaries between cell types. Surprisingly, movement of SHR::GFP was observed when ectopic expression from an epidermal promoter was placed in a scarecrow (scr) mutant background, revealing a possible role for SCR in limiting movement. Analysis of the competence to respond to SHR-mediated cell specification activity indicated that it was broadly distributed in the epidermal lineage, while competence to respond to the cell division activity of SHR appeared limited to the initials and involved induction of SCR. The spatial distribution of competence to respond to SHR highlights the importance of tightly regulated movement in generating the root radial pattern.
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Affiliation(s)
- Giovanni Sena
- NYU, Department of Biology, The Silver Center, room 1009, 100 Washington Square East, New York, NY 10003, USA
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92
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Spetz C, Valkonen JPT. Potyviral 6K2 protein long-distance movement and symptom-induction functions are independent and host-specific. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2004; 17:502-10. [PMID: 15141954 DOI: 10.1094/mpmi.2004.17.5.502] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Deletion of various portions, or insertion of six histidine residues (6xHis) into various positions of the membrane-bound 6K2 protein (53 amino acids) of Potato virus A (PVA, genus Potyvirus), inhibited systemic infection in Nicotiana tabacum and N. benthamiana plants. However, a spontaneous mutation (Gly2Cys) that occurred in 6K2 adjacent to the 6xHis insert placed between Ser1 and Gly2 enabled systemic infection in a single N. benthamiana plant. No symptoms were observed, but virus titers were similar to the symptom-inducing wild-type (wt) PVA. N. tabacum plants were not systemically infected, albeit virus propagation was observed in inoculated protoplasts. The 6xHis/Gly2Cys mutant was reconstructed in vitro and serially propagated by mechanical inoculation in N. benthamiana. Following the third passage, a novel viral mutant appeared, lacking the last four His residues of the insert, as well as the Gly2 and Thr3 of 6K2. It infected N. tabacum plants systemically, and in the systemically infected N. benthamiana leaves, vein chlorosis and mild yellowing symptoms were observed, typical of wt PVA infection. The mutant virus accumulated to titers similar to wt PVA in both hosts. These results show that the PVA 6K2 protein affects viral long-distance movement and symptom induction independently and in a host-specific manner.
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Affiliation(s)
- Carl Spetz
- Department of Plant Biology and Forest Genetics, Genetics Centre, SLU, PO Box 7080, SE-750 07 Uppsala, Sweden
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93
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Brill LM, Dechongkit S, DeLaBarre B, Stroebel J, Beachy RN, Yeager M. Dimerization of recombinant tobacco mosaic virus movement protein. J Virol 2004; 78:3372-7. [PMID: 15016859 PMCID: PMC371043 DOI: 10.1128/jvi.78.5.3372-3377.2004] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The p30 movement protein (MP) is essential for cell-to-cell spread of tobacco mosaic virus in planta. We used anion-exchange chromatography and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to obtain highly purified 30-kDa MP, which migrated as a single band in native PAGE. Analytical ultracentrifugation suggested that the protein was monodisperse and dimeric in the nonionic detergent n-octyl-beta-D-glucopyranoside. Circular dichroism (CD) spectroscopy showed that the detergent-solubilized protein contained significant alpha-helical secondary structure. Proteolysis of the C-tail generated a trypsin-resistant core that was a mixture of primarily monomers and some dimers. We propose that MP dimers are stabilized by electrostatic interactions in the C terminus as well as hydrophobic interactions between putative transmembrane alpha-helical coiled coils.
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Affiliation(s)
- Laurence M Brill
- Department of Cell Biology, The Scripps Research Institute, Scripps Clinic, La Jolla, California 92037, USA
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94
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Mariano AC, Andrade MO, Santos AA, Carolino SMB, Oliveira ML, Baracat-Pereira MC, Brommonshenkel SH, Fontes EPB. Identification of a novel receptor-like protein kinase that interacts with a geminivirus nuclear shuttle protein. Virology 2004; 318:24-31. [PMID: 14972531 DOI: 10.1016/j.virol.2003.09.038] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2003] [Accepted: 09/26/2003] [Indexed: 11/21/2022]
Abstract
Despite extensive studies in plant virus-host interactions, the molecular mechanisms of geminivirus movement and interactions with host components remain largely unknown. A tomato kinase protein and its soybean homolog were found to interact specifically with the nuclear shuttle protein (NSP) of Tomato golden mosaic virus (TGMV) and Tomato crinkle leaf yellows virus (TCrLYV) through yeast two-hybrid screening and in vitro protein binding assays. These proteins, designated LeNIK (Lycopersicon esculentum NSP-Interacting Kinase) and GmNIK (Glycine max NIK), belong to the LRR-RLK (leucine rich-repeat receptor-like kinase) family that is involved in plant developmental processes and/or resistance response. As such, NIK is structurally organized into characteristic domains, including a serine/threonine kinase domain with a nucleotide binding site at the C-terminal region, an internal transmembrane segment and leucine-rich repeats (LRR) at the N-terminal portion. The potential significance of the NSP-NIK interaction is discussed.
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Affiliation(s)
- Andrea C Mariano
- Departamento de Bioquímica e Biologia Molecular, Universidade Federal de Viçosa, 36571.000 Viçosa, MG, Brazil
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95
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Heinlein M, Epel BL. Macromolecular Transport and Signaling Through Plasmodesmata. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 235:93-164. [PMID: 15219782 DOI: 10.1016/s0074-7696(04)35003-5] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Plasmodesmata (Pd) are channels in the plant cell wall that in conjunction with associated phloem form an intercellular communication network that supports the cell-to-cell and long-distance trafficking of a wide spectrum of endogenous proteins and ribonucleoprotein complexes. The trafficking of such macromolecules is of importance in the orchestration of non-cell autonomous developmental and physiological processes. Plant viruses encode movement proteins (MPs) that subvert this communication network to facilitate the spread of infection. These viral proteins thus represent excellent experimental keys for exploring the mechanisms involved in intercellular trafficking and communication via Pd.
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Affiliation(s)
- Manfred Heinlein
- Botanical Institute, University of Basel, Hebelstrasse 1, CH-4056 Basel, Switzerland
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96
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Oparka KJ. Getting the message across: how do plant cells exchange macromolecular complexes? TRENDS IN PLANT SCIENCE 2004; 9:33-41. [PMID: 14729217 DOI: 10.1016/j.tplants.2003.11.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
A major pathway for macromolecular exchange in plants involves plasmodesmata (PD), the small pores that connect adjoining cells. This article considers the nature of macromolecular complexes (MCs) that pass through PD and the pathways and mechanisms that guide them to the PD pore. Recent cell-biological studies have identified proteins involved in the directional trafficking of MCs to PD, and yeast two-hybrid studies have isolated novel host proteins that interact with viral movement proteins. Collectively, these studies are yielding important clues in the search for components that compose the plant intercellular MC trafficking pathway. Here, they are placed in the context of a functional model that links the cytoskeleton, chaperones and secretory pathway in the intercellular trafficking of MCs.
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Affiliation(s)
- Karl J Oparka
- Cell-to-Cell Communication Programme, Scottish Crop Research Institute, Invergowrie, DD2 5DA, Dundee, UK.
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97
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Dorokhov YL, Skurat EV, Frolova OY, Gasanova TV, Smirnov AA, Zvereva SD, Ivanov PA, Ravin NV, Zamchuk LI, Atabekov IG. Reciprocal dependence between pectinmethylesterase gene expression and tobamovirus reproduction effectiveness in Nicotiana benthamiana. DOKL BIOCHEM BIOPHYS 2004; 394:30-2. [PMID: 15116563 DOI: 10.1023/b:dobi.0000017148.30969.4f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Yu L Dorokhov
- Belozerskii Institute of Physicochemical Biology, Moscow State University, Moscow, 119992 Russia
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98
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Abstract
Tobacco mosaic virus (TMV) has had an illustrious history for more than 100 years, dating to Beijerinck's description of the mosaic disease of tobacco as a contagium vivum fluidum and the modern usage of the word "virus." Since then, TMV has been acknowledged as a preferred didactic model and a symbolic model to illuminate the essential features that define a virus. TMV additionally emerged as a prototypic model to investigate the biology of host plants, namely tobacco. TMV also exemplifies how a model system furthers novel, and often unexpected, developments in biology and virology. Today, TMV is used as a tool to study host-pathogen interactions and cellular trafficking, and as a technology to express valuable pharmaceutical proteins in tobacco. The history of TMV illustrates how pragmatic strategies to control an economically important disease of tobacco have had unexpected and transforming effects across platforms that impinge on plant health and public health.
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Affiliation(s)
- Karen-Beth G Scholthof
- Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843-2132, USA.
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99
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Ivanov KI, Puustinen P, Gabrenaite R, Vihinen H, Rönnstrand L, Valmu L, Kalkkinen N, Mäkinen K. Phosphorylation of the potyvirus capsid protein by protein kinase CK2 and its relevance for virus infection. THE PLANT CELL 2003; 15:2124-39. [PMID: 12953115 PMCID: PMC181335 DOI: 10.1105/tpc.012567] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2003] [Accepted: 06/18/2003] [Indexed: 05/19/2023]
Abstract
We reported previously that the capsid protein (CP) of Potato virus A (PVA) is phosphorylated both in virus-infected plants and in vitro. In this study, an enzyme that phosphorylates PVA CP was identified as the protein kinase CK2. The alpha-catalytic subunit of CK2 (CK2alpha) was purified from tobacco and characterized using in-gel kinase assays and liquid chromatography-tandem mass spectrometry. The tobacco CK2alpha gene was cloned and expressed in bacterial cells. Specific antibodies were raised against the recombinant enzyme and used to demonstrate the colocalization of PVA CP and CK2alpha in infected tobacco protoplasts. A major site of CK2 phosphorylation in PVA CP was identified by a combination of mass spectrometric analysis, radioactive phosphopeptide sequencing, and mutagenesis as Thr-242 within a CK2 consensus sequence. Amino acid substitutions that affect the CK2 consensus sequence in CP were introduced into a full-length infectious cDNA clone of PVA tagged with green fluorescent protein. Analysis of the mutant viruses showed that they were defective in cell-to-cell and long-distance movement. Using in vitro assays, we demonstrated that CK2 phosphorylation inhibited the binding of PVA CP to RNA, suggesting a molecular mechanism of CK2 action. These results suggest that the phosphorylation of PVA CP by CK2 plays an important regulatory role in virus infection.
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Affiliation(s)
- Konstantin I Ivanov
- Institute of Biotechnology, University of Helsinki, FIN-00014 Helsinki, Finland.
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100
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Kim JY, Yuan Z, Jackson D. Developmental regulation and significance of KNOX protein trafficking in Arabidopsis. Development 2003; 130:4351-62. [PMID: 12900451 DOI: 10.1242/dev.00618] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Intercellular communication delivers critical information for position-dependent specification of cell fate. In plants, a novel mechanism for cell-to-cell communication involves the intercellular trafficking of regulatory proteins and mRNAs. The maize KNOTTED1 (KN1) gene acts non cell-autonomously in the maize leaf, and KN1 was the first plant protein shown to traffic cell-to-cell, presumably through plasmodesmata. We have compared the intercellular trafficking of green fluorescent protein (GFP) fusions of KN1 and Arabidopsis KN1-related homeobox proteins to that of the viral movement protein from turnip vein clearing tobamovirus. We show that there is specific developmental regulation of GFP approximately KN1 trafficking. GFP -- KN1 was able to traffic from the inner layers of the leaf to the epidermis, but not in the opposite direction, from epidermis to mesophyll. However, GFP or the GFP -- movement protein fusion moved readily out of the epidermis. GFP -- KN1 was however able to traffic out of the epidermal (L1) layer in the shoot apical meristem, indicating that KN1 movement out of the L1 was developmentally regulated. GFP -- KNAT1/BREVIPEDICELLUS and GFP -- SHOOTMERISTEMLESS fusions could also traffic from the L1 to the L2/L3 layers of the meristem. In a test for the functional significance of trafficking, we showed that L1-specific expression of KN1 or of KNAT1 was able to partially complement the strong shootmeristemless-11 (stm-11) mutant. However, a cell-autonomous GUS fusion to KN1 showed neither trafficking ability nor complementation of stm-11 when expressed in the L1. These results suggest that the activity of KN1 and related homeobox proteins is maintained following intercellular trafficking, and that trafficking may be required for their normal developmental function.
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Affiliation(s)
- Jae-Yean Kim
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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