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At least 595 records · Page 33Linked to original sources
PubMed1975

Assembly of a rod-shaped virus. Disk aggregate of cucumber green mottle mosaic virus protein and its function.

Although it is established that in the assembly of tobacco mosaic virus (TMV) in vitro, a 20 S disk aggregate of protein is essential for the initiation of the reaction, there is no agreement as to whether subsequent rod elongation proceeds by the addition of protein subunits or disks. Cucumber green mottle mosaic virus (CGMMV) is a rod-shaped virus closely related to TMV. It was observed directly by electron microscopy that CGMMV-protein also formed a single- or double-layer disk aggregate under conditions where reconstitution with the protein and TMV-RNA proceeds efficiently. Whichever forms, a single or double layer, a disk aggregate is required for the initiation of reconstitution, but cannot participate in rod elongation. These results obtained with CGMMV support our model proposed for the mechanism of assembly of TMV and rod-shaped viruses; i.e., the assembly occurs in two steps; disk aggregates of protein are essential only for initiation, and rod eleongation proceeds by subsequent addition of subunits.

Drug Stability↗
PubMed2005

Involvement of the small GTPase Rac in the defense responses of tobacco to pathogens.

During the hypersensitive response (HR), plants accumulate reactive oxygen species (ROS) that are likely generated at least in part by an NADPH oxidase similar to that found in mammalian neutrophils. An essential regulator of mammalian NADPH oxidase is the small GTP-binding protein Rac. To investigate whether Rac also regulates the pathogen-induced oxidative burst in plants, a dominant negative form of the rice OsRac1 gene was overexpressed in tobacco carrying the N resistance gene. Following infection with Tobacco mosaic virus (TMV), DN-OsRacl plants developed smaller lesions than wild-type plants, accumulated lower levels of lipid peroxidation products, and failed to activate expression of antioxidant genes. These results, combined with the demonstration that superoxide and hydrogen peroxide levels were reduced in DN-OsRacl tobacco developing a synchronous HR triggered by transient expression of the TMV p50 helicase domain or the Pto and AvrPto proteins, suggest that ROS production is impaired. The dominant negative effect of DN-OsRacl could be rescued by transiently overexpressing the wild-type OsRac1 protein. TMV-induced salicylic acid accumulation also was compromised in DN-OsRacl tobacco. Interestingly, while systemic acquired resistance to TMV was not impaired, nonhost resistance to Pseudomonas syringae pv. maculicola ES4326 was suppressed. Thus, the effect DN-OsRac1 expression exerts on the resistance signaling pathway appears to vary depending on the identity of the inoculated pathogen.

Gene Expression Regulation, Plant↗
PubMedDate not supplied

A new multigene family inducible by tobacco mosaic virus or salicylic acid in tobacco.

A previously undescribed cDNA family was isolated from tobacco challenged with tobacco mosaic virus (TMV). A cDNA library was constructed with mRNA from upper leaves of Xanthi nc tobacco plants that had been inoculated with TMV on the lower leaves 11 days previously. The library was screened differentially with radiolabeled cDNA synthesized with mRNA from upper, uninoculated leaves of either TMV-inoculated or mock-inoculated tobacco plants. The new cDNA family, designated SAR8.2, had at least five expressed members, one or more of which were inducible by TMV inoculation and by salicylic acid treatment. The cDNAs encoded small, highly basic proteins containing N-terminal hydrophobic signal peptides and highly conserved cysteine-rich C-terminal domains. One of the SAR8.2 family members contained a direct repeat of the C-terminal domain in tandem. Hybridization of SAR8.2 cDNA to tobacco genomic DNAs indicated a gene family of 10-12 members.

Amino Acid Sequence↗
PubMedDate not supplied

Evidence for proteolytic processing of tobacco mosaic virus movement protein in Arabidopsis thaliana.

Two ecotypes of Arabidopsis thaliana were transformed with the gene encoding tobacco mosaic virus (TMV) movement protein (P30). P30 accumulated largely in a subcellular fraction containing cell wall components and as a soluble protein. The protein migrated in denaturing gels with an M(r) of 30K, significantly faster than P30 (M(r) approximately 34K) accumulating after expression in transgenic tobacco, Escherichia coli or Spodoptera frugiperda cells, or after virus multiplication in tobacco. The P30 from A. thaliana infected with TMV for 14 days comigrated with that from E. coli, but that from A. thaliana infected for 49 days was of the smaller size. The use of antisera specific for the N- or C-termini of P30 showed that in A. thaliana P30 was proteolytically processed at the N-terminus, a region essential for P30 function. The failure of these plants to complement a TMV P30 mutant indicated that processed P30 was nonfunctional, although the processing was not so rapid that it prevented the development of systemic infections with wild type TMV. The absence of detectable P30 phosphorylation in A. thaliana demonstrated that phosphorylation was not essential for movement protein function and suggested that this species may use proteolytic cleavage of the N-terminus as an alternative strategy to tobacco for deactivating P30.

Animals↗
PubMed1976

The region of tobacco mosaic virus RNA involved in the nucleation of assembly.

The interaction of TMV RNA with the disk aggregate of TMV protein at the initiation of assembly has been studied by using the techniques of RNA sequencing. The 5' end group has been identified, and shown not to be protected in the early stages of assembly from accessibility to nuclease digestion. A population of RNA fragments of average length 250 nucleotides, originating from a unique region of TMV RNA, is encapsidated by limited assembly, and sufficient sequence information is available to identify certain unusual features. The protected region does not contain highly reiterated simple repeating sequences, but may contain more complicated repeats. The length and complexity of the nucleation region may reflect adaptation to the efficient mediation of the conformational change from disk to helix of TMV protein, besides a requirement for binding to the disk, and this may be an important part of the mechanism of specificity in the nucleation of assembly.

Electrophoresis↗
PubMed1999

Elucidation of the genome organization of tobacco mosaic virus.

Proteins unique to tobacco mosaic virus (TMV)-infected plants were detected in the 1970s by electrophoretic analyses of extracts of virus-infected tissues, comparing their proteins to those generated in extracts of uninfected tissues. The genome organization of TMV was deduced principally from studies involving in vitro translation of proteins from the genomic and subgenomic messenger RNAs. The ultimate analysis of the TMV genome came in 1982 when P. Goelet and colleagues sequenced the entire genome. Studies leading to the elucidation of the TMV genome organization are described below.

Capsid Proteins↗
PubMed1982

Translational competition between related virus RNA species in cell-free systems.

The competition between the RNAs from two tobacco mosaic virus (TMV) strains for translation in rabbit reticulocyte lysate and wheat germ cell-free systems was investigated. The virus translational products were distinguished by the size difference of the I2 polypeptides. The RNAs of the two strains were translated simultaneously if added to the translation system together at the beginning of the reaction. Each of the TMV RNAs could inhibit translation of the other when the reaction was initiated by the RNA of one strain and that of the other strain was added after active translation had commenced. In contrast, translation of alfalfa mosaic virus (AMV) RNA was not appreciably inhibited when its RNA was added after the start of translation of TMV RNA; the addition of TMV RNA to an AMV RNA-initiated reaction also resulted in independent synthesis of the products of both virus RNAs.

Cell-Free System↗
PubMed1993

Inhibition of in vitro cotranslational disassembly of tobacco mosaic virus by monoclonal antibodies to the viral coat protein.

It has been shown by others that translation of tobacco mosaic virus (TMV) RNA may begin before uncoating of particles is complete. We provide evidence that this cotranslational disassembly can be inhibited by incubating TMV treated at pH 8 with certain monoclonal antibodies (MAbs) specific for TMV coat protein. The most efficient inhibition was achieved by incubation with some anti-metatope MAbs known to bind to the TMV extremity that becomes disassembled first and contains the 5' end of the RNA, as well as with some anti-cryptotope MAbs that bind only to dissociated coat protein subunits.

Antibodies, Monoclonal↗
PubMed1995

Differences in the subcellular localization of tobacco mosaic virus and cucumber mosaic virus movement proteins in infected and transgenic plants.

Our study reveals differences in the way that tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) movement proteins (MPs) partition with cellular components separated into four fractions from different aged leaves of infected and transgenic plants. Immunoblot analyses showed that TMV and CMV MPs associated predominantly with components in the cell wall fractions from leaves of transgenic plants. In infected tissue, highest levels of TMV MP were found in the organelle fractions from young and middle-aged leaves whereas most of the CMV MP was found in the detergent wash of the cell wall fraction. These results remained consistent even when plants were doubly infected with TMV and CMV. These results imply that MPs of plant viruses from different taxonomic groups differentially associate with subcellular components and that MP produced by a viral infection is targeted to additional subcellular destinations than MP produced in transgenic plants.

Cell Fractionation↗
PubMed2000

The GCD10 subunit of yeast eIF-3 binds the methyltransferase-like domain of the 126 and 183 kDa replicase proteins of tobacco mosaic virus in the yeast two-hybrid system.

The tobacco mosaic virus (TMV) replicase complex contains virus- and host-encoded proteins. In tomato, one of these host proteins was reported previously to be related serologically to the GCD10 subunit of yeast eIF-3. The yeast two-hybrid system has now been used to show that yeast GCD10 interacts selectively with the methyltransferase domain shared by the 126 and 183 kDa TMV replicase proteins. These findings are consistent with a role for a GCD10-like protein in the TMV replicase complex and suggest that, in TMV-infected cells, the machinery of virus replication and protein synthesis may be closely connected.

Eukaryotic Initiation Factor-3↗
PubMed2004

High-level expression of alternative oxidase protein sequences enhances the spread of viral vectors in resistant and susceptible plants.

The alternative oxidase (AOX) is the terminal oxidase of the cyanide-resistant alternative respiratory pathway in plants and has been implicated in resistance to viruses. When tobacco mosaic virus (TMV) vectors were used to drive very high levels of expression of either AOX or AOX mutated in its active site (AOX-E), virus spread was enhanced. This was visualized as the induction of larger hypersensitive-response lesions after inoculation onto NN-genotype tobacco than those produced by vectors bearing sequences of comparable length [the green fluorescent protein (gfp) gene sequence or antisense aox] or the 'empty' viral vector. Also, in the highly susceptible host Nicotiana benthamiana, systemic movement of TMV vectors expressing AOX or AOX-E was faster than that of TMV constructs bearing gfp or antisense aox sequences. Notably, in N. benthamiana, TMV.AOX and TMV.AOX-E induced symptoms that were severe and ultimately included cell death, whereas the empty vector, TMV.GFP and the TMV vector expressing antisense aox sequences never induced necrosis. The results show that, if expressed at sufficiently high levels, active and inactive AOX proteins can affect virus spread and symptomology in plants.

Apoptosis↗
PubMed1990

RNA pseudoknot domain of tobacco mosaic virus can functionally substitute for a poly(A) tail in plant and animal cells.

The genomes of many RNA viruses terminate in a tertiary structure similar to the L-conformation of tRNAs and this structure is recognized by many tRNA-specific enzymes such as aminoacyl-tRNA synthetase. Virtually the entire 3'-untranslated region (UTR) of tobacco mosaic virus (TMV) RNA is involved in an extended tertiary structure containing, in addition to a tRNA-like structure, a pseudoknot domain that lies immediately upstream. Although the functions of these structures are not well understood, they are essential to the virus. We demonstrate that the addition of the 204-base TMV 3'-untranslated region to foreign mRNA constructs can increase gene expression up to 100-fold compared to nonadenylated mRNA. The 3'-UTR of TMV was equal to or greater than a polyadenylated tail in enhancing gene expression in electroporated dicot and monocot protoplasts. The TMV 3'-UTR is functionally similar to a polyadenylated tail in that it increases mRNA stability and translation and must be positioned at the 3' terminus to function efficiently. Similar effects on expression were observed in Chinese hamster ovary cells, demonstrating that the sequence functions in a wide range of eukaryotes. When the extended tertiary structure was dissected, the upstream pseudoknot domain was found to be largely responsible for increasing expression. The inclusion of the tRNA-like structure, however, was important for full regulation.

Animals↗
PubMed2002

A strobilurin fungicide enhances the resistance of tobacco against tobacco mosaic virus and Pseudomonas syringae pv tabaci.

The strobilurin class of fungicides comprises a variety of synthetic plant-protecting compounds with broad-spectrum antifungal activity. In the present study, we demonstrate that a strobilurin fungicide, F 500 (Pyraclostrobin), enhances the resistance of tobacco (Nicotiana tabacum cv Xanthi nc) against infection by either tobacco mosaic virus (TMV) or the wildfire pathogen Pseudomonas syringae pv tabaci. F 500 was also active at enhancing TMV resistance in NahG transgenic tobacco plants unable to accumulate significant amounts of the endogenous inducer of enhanced disease resistance, salicylic acid (SA). This finding suggests that F 500 enhances TMV resistance in tobacco either by acting downstream of SA in the SA signaling mechanism or by functioning independently of SA. The latter assumption is the more likely because in infiltrated leaves, F 500 did not cause the accumulation of SA-inducible pathogenesis-related (PR)-1 proteins that often are used as conventional molecular markers for SA-induced disease resistance. However, accumulation of PR-1 proteins and the associated activation of the PR-1 genes were elicited upon TMV infection of tobacco leaves and both these responses were induced more rapidly in F 500-pretreated plants than in the water-pretreated controls. Taken together, our results suggest that F 500, in addition to exerting direct antifungal activity, may also protect plants by priming them for potentiated activation of subsequently pathogen-induced cellular defense responses.

Antifungal Agents↗
PubMed2002

Salicylic acid has cell-specific effects on tobacco mosaic virus replication and cell-to-cell movement.

Tobacco mosaic virus (TMV) and Cucumber mosaic virus expressing green fluorescent protein (GFP) were used to probe the effects of salicylic acid (SA) on the cell biology of viral infection. Treatment of tobacco with SA restricted TMV.GFP to single-epidermal cell infection sites for at least 6 d post inoculation but did not affect infection sites of Cucumber mosaic virus expressing GFP. Microinjection experiments, using size-specific dextrans, showed that SA cannot inhibit TMV movement by decreasing the plasmodesmatal size exclusion limit. In SA-treated transgenic plants expressing TMV movement protein, TMV.GFP infection sites were larger, but they still consisted overwhelmingly of epidermal cells. TMV replication was strongly inhibited in mesophyll protoplasts isolated from SA-treated nontransgenic tobacco plants. Therefore, it appears that SA has distinct cell type-specific effects on virus replication and movement in the mesophyll and epidermal cell layers, respectively. Thus, SA can have fundamentally different effects on the same pathogen in different cell types.

Cucumovirus↗
PubMed2002

Effect of yeast CTA1 gene expression on response of tobacco plants to tobacco mosaic virus infection.

The response of tobacco (Nicotiana tabacum L. cv Xanthi-nc) plants with elevated catalase activity was studied after infection by tobacco mosaic virus (TMV). These plants contain the yeast (Saccharomyces cerevisiae) peroxisomal catalase gene CTA1 under the control of the cauliflower mosaic virus 35S promoter. The transgenic lines exhibited 2- to 4-fold higher total in vitro catalase activity than untransformed control plants under normal growth conditions. Cellular localization of the CTA1 protein was established using immunocytochemical analysis. Gold particles were detected mainly inside peroxisomes, whereas no significant labeling was detected in other cellular compartments or in the intercellular space. The physiological state of the transgenic plants was evaluated in respect to growth rate, general appearance, carbohydrate content, and dry weight. No significant differences were recorded in comparison with non-transgenic tobacco plants. The 3,3'-diaminobenzidine-stain method was applied to visualize hydrogen peroxide (H(2)O(2)) in the TMV infected tissue. Presence of H(2)O(2) could be detected around necrotic lesions caused by TMV infection in non-transgenic plants but to a much lesser extent in the CTA1 transgenic plants. In addition, the size of necrotic lesions was significantly bigger in the infected leaves of the transgenic plants. Changes in the distribution of H(2)O(2) and in lesion formation were not reflected by changes in salicylic acid production. In contrast to the local response, the systemic response in upper noninoculated leaves of both CTA1 transgenic and control plants was similar. This suggests that increased cellular catalase activity influences local but not systemic response to TMV infection.

Catalase↗
PubMed2003

Genetic modification of alternative respiration has differential effects on antimycin A-induced versus salicylic acid-induced resistance to Tobacco mosaic virus.

Salicylic acid (SA), a natural defensive signal chemical, and antimycin A, a cytochrome pathway inhibitor, induce resistance to Tobacco mosaic virus (TMV). Pharmacological evidence suggested signaling during resistance induction by both chemicals involved alternative oxidase (AOX), sole component of the alternative respiratory pathway (AP). Roles of the AP include regulation of intramitochondrial reactive oxygen species and maintenance of metabolic homeostasis. Transgenic tobacco (Nicotiana tabacum) with modified AP capacities (2- to 3-fold increased or decreased) showed no alteration in phenotype with respect to basal susceptibility to TMV or the ability to display SA-induced resistance to systemic viral disease. However, in directly inoculated tissue, antimycin A-induced TMV resistance was inhibited in plants with increased AP capacities, whereas SA and antimycin A-induced resistance was transiently enhanced in plant lines with decreased AP capacities. We conclude that SA-induced TMV resistance results from activation of multiple mechanisms, a subset of which are inducible by antimycin A and influenced by AOX. Other antiviral factors, potentially including the SA-inducible RNA-dependent RNA polymerase, are regulated by AOX-independent mechanisms.

Antimycin A↗
PubMed2004

Capsicum annuum tobacco mosaic virus-induced clone 1 expression perturbation alters the plant's response to ethylene and interferes with the redox homeostasis.

Capsicum annuum tobacco mosaic virus (TMV)-induced clone 1 (CaTin1) gene was expressed early during incompatible interaction of hot pepper (Caspsicum annuum) plants with TMV and Xanthomonas campestris. RNA-blot analysis showed that CaTin1 gene was expressed only in roots in untreated plants and induced mainly in leaf in response to ethylene, NaCl, and methyl viologen but not by salicylic acid and methyl jasmonate. The ethylene dependence of CaTin1 induction upon TMV inoculation was demonstrated by the decrease of CaTin1 expression in response to several inhibitors of ethylene biosynthesis or its action. Transgenic tobacco (Nicotiana tabacum) plants expressing CaTin1 gene in sense- or antisense-orientation showed interesting characteristics such as the accelerated growth and the enhanced resistance to biotic as well as abiotic stresses. Such characteristics appear to be caused by the elevated level of ethylene and H2O2. Moreover, in transgenic plants expressing antisense CaTin1 gene, the expression of some pathogenesis-related genes was enhanced constitutively, which may be mainly due to the increased ethylene level. The promoter of CaTin1 has four GCC-boxes, two AT-rich regions, and an elicitor-inducible W-box. The induction of the promoter activity by ethylene depends on GCC-boxes and by TMV on W-box. Taken together, we propose that the CaTin1 up-regulation or down-regulation interferes with the redox balance of plants leading to the altered response to ethylene and biotic as well as abiotic stresses.

Acetates↗
PubMed1993

Molecular cloning and expression of a new class of ortho-diphenol-O-methyltransferases induced in tobacco (Nicotiana tabacum L.) leaves by infection or elicitor treatment.

In tobacco (Nicotiana tabacum L. cv Samsun NN), three distinct enzymes account for ortho-diphenol-O-methyltransferase (OMT) activity. OMT I is the major enzyme of healthy leaves, whereas enzymes OMT II and III are preferentially induced during the hypersensitive reaction to tobacco mosaic virus (TMV). Using an anti-OMT III antiserum, we isolated a partial OMT III cDNA clone by immunoscreening an expression library made from mRNA of TMV-infected tobacco leaves. Using this OMT III clone as a probe, we isolated a full-length clone with a deduced amino acid sequence encompassing all of the sequences obtained by Edman degradation of both purified proteins II and III. Thus, OMT II and III of tobacco are likely to be encoded by the same genes and to arise from different posttranslational modifications. Sequence analysis showed that this OMT clone represents a new class of OMT enzymes (class II) with a low level of similarity (53-58%) to OMTs cloned previously from other dicotyledonous plants. Southern analysis indicated that a small family of class II OMT genes inherited from ancestors related to Nicotiana sylvestris and Nicotiana tomentosiformis occurs in the tobacco genome. RNA blot analysis demonstrated that class II OMT genes, unlike class I OMT genes, are not expressed at a high constitutive level in lignified tissues of tobacco. Class II OMT transcripts were found to accumulate in tobacco leaves infected with TMV or treated with megaspermin, a proteinaceous elicitor from Phytophthora megasperma, but not in leaves treated with salicylic acid, a molecule known to trigger many defense genes. In TMV-infected or elicitor-treated tissues, a marked increase in catechol-methylating activity accompanied the accumulation of class II OMT gene products.

Amino Acid Sequence↗