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PubMed2006

Pyrene-stacked nanostructures constructed in the recombinant tobacco mosaic virus rod scaffold.

The effect of pyrenes introduced into a tobacco mosaic virus (TMV) coat protein monomer on the formation and stability of the TMV assembly was investigated. The possible arrangement of the pyrenes in the inner cavity of the TMV rod was also estimated. The pyrene derivative was introduced to four specific amino acids in the cavity of the TMV rod structure. Rod-structure formation was examined by atomic force microscopy (AFM). Two pyrene-attached mutants (positions 99 and 100) assembled to increase the length of the rod structures by 2.5 microm at pH 5.5. The interaction of the pyrene moieties in the TMV cavity was investigated by steady-state and time-resolved spectroscopic analysis. Strong excimer emission with significantly short wavelength (465 nm) was observed from the two mutants mentioned above. Excitation and UV-visible spectra indicate that the pyrene moieties form pi-stacked structures in the TMV cavity. Details of the pyrene interaction were investigated by analyzing the fluorescence lifetime of the excimer. Results suggest that the pyrenes formed preassociated rigid structures with partially overlapped geometry in the restricted space of the TMV cavity. The pyrenes effectively stabilize the TMV rod through a pi-stacking interaction in a well-ordered way, and the single pyrene moiety introduced into the monomer affects the overall formation of the TMV rod structure.

Capsid Proteins↗
PubMed1996

Cell-to-cell transport of movement-defective cucumber mosaic and tobacco mosaic viruses in transgenic plants expressing heterologous movement protein genes.

To determine if the movement proteins (MPs) of cucumber mosaic cucumovirus (CMV) and tobacco mosaic tobamovirus (TMV) are complementary in function, transgenic plants expressing genes encoding TMV or CMV MP were inoculated with movement-defective mutants of TMV and CMV. Transgenic plants expressing the MP gene of CMV strain S (subgroup II) complemented the cell-to-cell and systemic spread of a movement-defective mutant of CMV strain Fny (subgroup I) but not the local or systemic spread of a movement-defective mutant of TMV. Plants that contained the MP gene from CMV-S were not resistant to wild-type TMV infection. When inoculated with a movement-defective mutant of TMV that produced beta-glucuronidase, transgenic plants with the CMV MP gene supported only subliminal infection. Conversely, immunodetection and in situ localization techniques revealed that transgenic plants accumulating the TMV MP supported cell-to-cell spread, but not systemic transport, of a movement-defective CMV. These studies suggest that the transgenic TMV MP shares some of the functions with the CMV MP required to transport CMV, whereas the transgenic CMV MP is deficient in functions that are needed to mobilize the spread of TMV infection.

Amino Acid Sequence↗
PubMed1996

Mapping of host range restriction of the rakkyo strain of tobacco mosaic virus in Nicotiana tabacum cv. bright yellow.

The rakkyo strain (TMV-R) and the common strain (TMV-U1) of tobacco mosaic virus exhibit distinct host range differences. TMV-R infects rakkyo plants, a monocot host that TMV-U1 is unable to infect. However, TMV-R causes only latent infection in Nicotiana tabacum cv. Bright Yellow (BY) in inoculated leaves, whereas TMV-U1 infects BY systemically and induces mosaic symptoms. Complete nucleotide sequencing of the TMV-R genomic RNA revealed amino acid changes in the 130K/ 180K replicase proteins, the 30K protein, and the coat protein and nucleotide changes in the 5' and 3' noncoding regions compared to TMV-U1. To identify viral components involved in determination of differences in host range, we have mapped determinants for the differential infection phenotype in BY plants by constructing chimeric viruses between the two strains in the present study. Examination of the infection phenotypes of the 14 constructed chimeric viruses in BY showed that determinants defining the differential infection phenotype in BY reside in the 130K/180K replicase proteins and the 3' noncoding region. Cognate combination of the 130K/180K replicase proteins and the 3' noncoding region of TMV-U1 origin is required to produce systemic infection in BY plants.

DNA-Directed DNA Polymerase↗
PubMed1996

Complete nucleotide sequence and synthesis of infectious in vitro transcripts from a full-length cDNA clone of a rakkyo strain of tobacco mosaic virus.

The complete nucleotide sequence of the genome of a rakkyo strain of tobacco mosaic virus (TMV-R), which exhibits distinct host range differences from the common strain of TMV, was determined. The overall nucleotide sequence homology with TMV-U1 (a common strain of TMV) is 94.2%. The amino acid sequence homologies of the four encoded proteins (180K, 130K, 30K, coat protein) are from 95.9% to 98.0% compared with TMV-U1. To facilitate the analysis of the novel host range of TMV-R, a full-length clone of the genome containing a bacteriophage T7 RNA polymerase promoter was assembled from two cDNA clones and designated pRF3. In vitro transcripts derived from pRF3 were highly infectious. The infections of RF3, wild-type TMV-R, and U3/12-4 (derived from pU3/12-4, an infectious clone of TMV-U1) were compared on Nicotiana tabacum cv. Bright Yellow (BY) plants. No systemic mosaic symptoms were observed on plants inoculated with RF3 and TMV-R, while BY plants inoculated with U3/12-4 developed distinct mosaic symptoms on the upper leaves 8-9 days post-inoculation. The green fluorescent protein (GFP) gene was introduced into pRF3 and pU3/12-4 by replacing the coat protein gene to get two GFP expressing chimeric virus clones: pR-GFP or pU1-GFP. Transcripts from pU1-GFP produced strong fluorescence when inoculated onto BY leaves, while those from pR-GFP produced only very faint fluorescence.

Amino Acid Sequence↗
PubMed1996

A ribozyme gene and an antisense gene are equally effective in conferring resistance to tobacco mosaic virus on transgenic tobacco.

Ribozymes of the hammerhead class can be designed to cleave a target RNA in a sequence-specific manner and can potentially be used to specifically modulate gene activity. We have targeted the tobacco mosaic virus (TMV) genome with a ribozyme containing three catalytic hammerhead domains embedded within a 1 kb antisense RNA. The ribozyme was able to cleave TMV RNA at all three target sites in vitro at 25 degrees C. Transgenic tobacco plants were generated which expressed the ribozyme or the corresponding antisense constructs directed at the TMV genome. Six of 38 independent transgenic plant lines expressing the ribozyme and 6 of 39 plant lines expressing the antisense gene showed some level of protection against TMV infection. Homozygous progeny of some lines were highly resistant to TMV; at least 50% of the plants remained asymptomatic even when challenged with high levels of TMV. These plants also displayed resistance to infection with TMV RNA or the related tomato mosaic virus (ToMV). In contrast, hemizygous plants of the same lines displayed only very weak resistance when inoculated with low amounts of TMV and no resistance against high inoculation levels. Resistance in homozygous plants was not overcome by a TMV strain which was altered at the three target sites to abolish ribozyme-mediated cleavage, suggesting that the ribozyme conferred resistance primarily by an antisense mechanism.

Base Sequence↗
PubMed2005

Tumour-derived microvesicles carry several surface determinants and mRNA of tumour cells and transfer some of these determinants to monocytes.

This study was designed to determine the characteristics of tumour cell-derived microvesicles (TMV) and their interactions with human monocytes. TMV were shed spontaneously by three different human cancer cell lines but their release was significantly increased upon activation of the cells with phorbol 12-myristate 13-acetate (PMA). TMV showed the presence of several surface determinants of tumour cells, e.g. HLA class I, CD29, CD44v7/8, CD51, chemokine receptors (CCR6, CX3CR1), extracellular matrix metalloproteinase inducer (EMMPRIN), epithelial cell adhesion molecule (EpCAM), but their level of expression differed from that on cells they originated from. TMV also carried mRNA for growth factors: vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), interleukin-8 (IL-8) and surface determinants (CD44H). TMV were localized at the monocytes surface following their short exposure to TMV, while at later times intracellularly. TMV transferred CCR6 and CD44v7/8 to monocytes, exerted antiapoptotic effect on monocytes and activated AKT kinase (Protein Kinase B). Thus, TMV interact with monocytes, alter their immunophenotype and biological activity. This implicates the novel mechanism by which tumour infiltrating macrophages may be affected by tumour cells not only by a direct cell to cell contact, soluble factors but also by TMV.

Adenocarcinoma↗
PubMed1997

Exercise performance and magnetic resonance imaging-determined thigh muscle volume in children.

This study examined the relationships between thigh muscle volume (TMV) and aerobic and anaerobic performance in children. A total of 32 children, 16 boys and 16 girls, aged 9.9 (0.3) years completed a treadmill running test to exhaustion for the determination of peak oxygen uptake (peak VO2) and a Wingate Anaerobic Test (WAnT) for the determination of peak power (PP) and mean power (MP). The volume of the right thigh muscle was determined using magnetic resonance imaging. TMV was not significantly different in boys and girls [2.39 (0.29) l vs 2.18 (0.38) l, P > 0.05]. Peak VO2 and MP were significantly higher in boys than girls (P < 0.01) whether expressed in absolute, mass-related or allometrically scaled terms. Absolute PP was not significantly different in boys and girls but mass-related and allometrically scaled values were higher in boys (P < 0.01). TMV was correlated with absolute peak VO2, PP and MP in both sexes (r = 0.52-0.89, P < 0.01). In boys, mass-related PP was correlated with TMV (r = 0.53, P < 0.01), and in girls mass-related peak VO2 was correlated with TMV (r = -0.61, P < 0.01). However, in neither sex were allometrically scaled peak VO2, PP or MP correlated with TMV (P > 0.05). There were no significant differences between boys and girls in terms of peak VO2, PP or MP when expressed in a ratio to TMV or allometrically scaled TMV. In conclusion, this study has demonstrated that, when body size is appropriately accounted for using allometric scaling, TMV is unrelated to indices of aerobic and anaerobic power in 10-year-old children. Furthermore, there appear to be no qualitative differences in the muscle function of boys and girls in respect of aerobic and anaerobic function.

Child↗
PubMed1988

Replication of chimeric tobacco mosaic viruses which carry heterologous combinations of replicase genes and 3' noncoding regions.

Three tobacco mosaic virus (TMV)-L (tomato strain)-derived chimeras, designated OL1, LG11, or LK31, were constructed by replacing the 3' noncoding region with the corresponding sequence of TMV-OM (common strain), cucumber green mottle mosaic virus (CGMMV), or TMV-Cc (cowpea strain), respectively. The genomic RNAs of TMV-L, -OM, and CGMMV carry histidine-accepting tRNA-like structures at their 3' termini, while the genome of TMV-Cc accepts valine. The three chimeric viruses were able to multiply in both tobacco protoplasts and plants. Multiplication of OL1 in protoplasts was similar to that of the parental strain, L, but in the cases of LG11 and LK31 multiplication was decreased. Sequence analyses of progeny RNAs revealed that viruses with chimeric sequences propagated. These data suggested that TMV-L replicase recognizes the 3' terminal structures of TMV-OM, CGMMV, and TMV-Cc and can initiate minus-strand RNA synthesis. The relationship between the virus-coded component(s) of TMV replicase and the 3' terminal region may not be so stringent.

Base Sequence↗
PubMed1990

Protection against tobacco mosaic virus infection in transgenic plants requires accumulation of coat protein rather than coat protein RNA sequences.

Transgenic tobacco plants which express a chimeric gene encoding the tobacco mosaic virus (TMV) coat protein (CP) and the TMV 3' untranslated region are protected against infection by TMV. In this study chimeric genes that encode the sequences representing the TMV CP subgenomic RNA, but do not produce protein (because of removal of the initiation codon), and RNA that lacks the tRNA-like sequence of the TMV 3' end were expressed in transgenic plants. Only plants that accumulated CP, regardless of the presence of absence of the 3' end of TMV-RNA, were protected against infection by TMV. The results indicate that the CP per se, rather than TMV RNA, is responsible for the resistance to infection by TMV. Furthermore, the degree of protection is dependent upon the level of accumulated CP.

Base Sequence↗
PubMed1986

Molecular assembly of tobacco mosaic virus in vitro.

TMV assembly starts with a specific interaction between the assembly origin on the RNA and a disk aggregate of coat protein. The assembly origin is located in the 30K protein cistron for common and tomato strains of TMV and in the coat protein cistron for cowpea strain of TMV and for CGMMV. All the assembly origins have three essential structures: a long base-paired hairpin loop structure; a target sequence, GAPuGUUG, at the top of the hairpin loop structure; and a tract where every third base is a purine. The protein aggregate responsible for the initiation of TMV assembly is a 20S disk, a two-layered aggregate of 34 protein subunits. The two layers of a disk open apart onto the central hole and this structure may be critical for the disk to interact with the assembly origin on the RNA. The target sequence may bind specifically to this structure. Although only a low concentration of 20S disks exists in the usual assembly condition, one disk is enough to initiate TMV assembly. TMV elongation proceeds in two directions. Elongation to the 5'-end proceeds rapidly by preferential incorporation of protein subunits (or A protein) and in 5-7 min gives rise to 260 nm intermediate particles whose 5'-end is coated. A model of elongation toward the 5'-end is shown in Fig. 15. Protected RNAs from nuclease digestion during the assembly reaction produce a banding pattern on gels by electrophoresis. The banding pattern reflects features of the RNA rather than protein that are used in the assembly reaction, since the pattern was the same for assembly between TMV-RNA and CGMMV protein subunits as for assembly between TMV-RNA and TMV protein containing 20S aggregates. The 20S aggregate in the assembly solution has a helical structure with 39 protein subunits rather than the disk structure. Rapid addition of 20S helical aggregates to the top of the growing rod seems to be impossible because of its topological complexity. Elongation toward the 3'-end does not start for at least the first 4 min after initiation. It probably cannot begin until the 5'-end RNA tail disappears into the intermediate rod. Elongation toward the 3'-end favors 20S aggregates as the protein source and gives rise to the full-length rods in about 30 min after the initiation. There are no topological difficulties in adding 20S helical aggregates to the protruding RNA tail.(ABSTRACT TRUNCATED AT 400 WORDS)

Genes, Viral↗
PubMed2004

Affinity purification of streptavidin using tobacco mosaic virus particles as purification tags.

A new protein affinity purification system has been developed. Recombinant tobacco mosaic virus (TMV) was used as an affinity matrix for isolation and purification of the given protein of interest. In model experiments, streptavidin-specific heptapeptide sequence TLIAHPQ was inserted into TMV coat protein near the C end. This oligopeptide did not interfere significantly with viral replication, assembly, and movement. Recombinant TMV functioned as an epitope tag recognizing streptavidin in plant protein extracts. Plant protein extracts containing streptavidin were incubated with recombinant TMV virions. Affinity complexes of viral particles with the protein of interest were collected by centrifugation. Recombinant TMV-streptavidin complex was dissociated with 0.2M acetic acid, pH 4.6, and was passed through membrane filter Nanosep 300K by centrifugation. The filtrate contained pure streptavidin. Recombinant TMV was left on the filter. TMV particles collected from the filter could be used for at least two more purification cycles. The streptavidin-specific recombinant TMV system was applied successfully for purification of streptavidin from Streptomyces avidinii. The authors believe that the TMV-based affinity system can also be used for the purification of other proteins.

Affinity Labels↗
PubMed2005

Effect of CuCl2 concentration on the aggregation and mineralization of Tobacco mosaic virus biotemplate.

Aggregation of the biotemplates in mineralization processes is a considerable obstacle in preparing well-dispersed bio-inorganic hybrid materials. In this study, aggregation and mineralization of Tobacco mosaic virus (TMV) biotemplates were investigated as a function of the copper precursor (CuCl2) concentration. The mean hydrodynamic radius of TMV in an aqueous CuCl2 solution was determined by dynamic light scattering for the monitoring of the TMV aggregation. At CuCl2 concentration of 0.5 mM or higher, the mean hydrodynamic radius of TMV increased dramatically indicating aggregation of the TMV particles. Numerical calculations on the long-range interaction energy between parallel model TMV particles agreed with the experimental observations for the TMV aggregation. Mineralization of copper precursors on the TMV biotemplates was achieved only at the CuCl2 concentrations that induced considerable aggregation of the biotemplate. From the numerical calculations and experimental results, it was concluded that a dense copper cluster deposition cannot be achieved without aggregation of TMV templates.

Copper↗
PubMed1985

Elongation in the major direction of tobacco mosaic virus assembly.

Butler and Lomonossoff [Butler, P. J. G. & Lomonossoff, G. P. (1978) J. Mol. Biol. 126, 877-882] claim that the elongation in the major direction (3'-->5') proceeds by incorporation of disk protein in tobacco mosaic virus (TMV) assembly. The strongest argument they have for this theory is the periodicity of 50 or 100 nucleotides that they observed in the banding pattern of the protected RNAs during the first few minutes of the assembly reaction. We repeated their experiment using TMV-OM (a common Japanese strain) disk protein and TMV-OM RNA. We observed a banding pattern similar to theirs, but we found the long protected RNA at 6 min to be from the 260-nm intermediate particle rather than from the full-length TMV RNA. We also carried out the assembly reaction between TMV-OM disk protein, as well as cucumber green mottle mosaic virus (CGMMV) protein, and three strains of TMV RNAs. During the course of each assembly reaction, we examined the banding patterns. We demonstrated that the banding pattern of the protected RNA differs depending on what kind of RNA is used, rather than on what kind of aggregational state the protein is in. Specifically, the similar banding pattern observed for CGMMV subunit protein was also observed for TMV disk protein in the assembly reaction with TMV (OM) RNA. We showed previously that the assembly reaction between CGMMV protein and TMV RNA proceeds by incorporation of CGMMV subunit protein. This strongly indicates that the banding pattern of the protected RNA does not arise from the stepwise addition of the 20S disk protein.

Journal Article↗
PubMed1986

cDNA cloning of the complete genome of tobacco mosaic virus and production of infectious transcripts.

The entire genome of tobacco mosaic virus (TMV) was copied into a series of subgenomic cDNA clones. cDNA sequences of the 5' and 3' ends of TMV were cloned separately. A synthetic oligonucleotide primer was used to generate a Pst I site at the 5' terminus, whereas a different primer was used to generate an Nde I site at the 3' terminus. This strategy permitted removal of non-TMV sequences from cloned cDNA inserts by treatment with exonuclease VII following restriction endonuclease cleavage. Pst I linkers were added to TMV 3' terminal cDNAs. Subgenomic cDNA fragments were ligated together into several independent full-genomic constructions from which TMV cDNA sequences could be cleanly excised as a single fragment by Pst I digestion. Full-genomic TMV cDNA was ligated immediately downstream from the lambda phage promoter from pPM1 and transcribed in vitro with Escherichia coli RNA polymerase. RNA transcripts from three of four full-genomic cDNA constructions were infectious, even though they contained 6 non-TMV nucleotides at the 3' end. Transcripts from a construction with 6 extra nucleotides at the 5' end also were infectious. Progeny virus from plants infected with cDNA transcripts appeared identical to the parental virus. Restriction maps of independent cDNA clones of the same regions of the genome were identical to each other and as predicted from the reported nucleotide sequence of TMV. Also, sequences of the 200 nucleotides proximal to the 5' termini of four independent cDNA clones were identical to each other and to published sequences, suggesting that independent isolates of TMV may have remarkably similar sequences.

Journal Article↗
PubMed1956

Studies on the aggregation reactions and basic dye binding of tobacco mosaic virus. I. Variation of pH, particle asymmetry, acid and base titration results, irreversible binding of methylene blue, ultraviolet absorption, and extent of heat denaturation in tobacco mosaic virus solutions with time of standing.

1. Aqueous solutions of tobacco mosaic virus were found to undergo a number of spontaneous changes on standing in the cold. The results of pH measurements, acid and base titrations, intrinsic viscosity determinations, studies on the irreversible binding of methylene blue with the virus, ultraviolet absorption, and the extent of nucleic acid splitting by heat denaturation indicated the occurrence of two successive reactions, the first one causing the release of hydrogen ions and a greater lability of the nucleic acid, and the second one, which involved end-to-end dimerization and which took place after 8 days of standing, requiring hydrogen ions. 2. The first over-all reaction was found to be a mixture of various types of reversible disaggregation and aggregation reactions, the nature of which depended on the pretreatment, the TMV concentration, the time of standing, and the phosphate concentration. For longer times of standing at high protein concentration a sudden drop in ultraviolet absorption is noted after dilution; also the drops in viscosity and pH are largest with a steep rise following, indicating the greatest breakup of end-to-end aggregates with formation of the side-to-side type. For concentrated solutions of TMV in water which have not stood long no drop in ultraviolet absorption is noted on dilution; the decrease in the other quantities is less, indicating that only a less extensive breakdown of end-to-end aggregates occurs. Addition of phosphate to concentrated solutions of TMV causes formation of side-to-side aggregates which break up on dilution. 3. Using the results for the pH increase and the viscosity increase in a given time interval for a given TMV preparation and also the slope of the corresponding titration curve at the pH mean, a value for the number of hydrogen ions taken up per TMV monomer in the formation of the end-to-end dimer was finally calculated. The average result obtained for two preparations was 3300. 4. Methylene blue, in the polymeric form, was demonstrated to cause complete irreversible conversion of TMV monomers to end-to-end dimers. At dye concentrations above 10(-4)M, higher TMV polymers are formed, but these are broken down to dimers on removal of free dye by dialysis. The irreversible binding ratios were shown to be decreased in accordance with the extent of the end-to-end aggregation of the preparation at the time of the experiment, which is in agreement with the concept that the irreversibly bound dye polymers go into the junction formed between two interacting TMV monomers. On the basis that only the monomers initially present in solution can react, maximum binding ratios corresponding to complete conversion of monomers to dimers were calculated from the observed irreversible binding ratios and from the fraction of dimers initially present which was obtained from viscosity data. The average result for three preparations in different states of aggregation was calculated to be 6565 for tetrameric binding or 3230 for dimeric binding, which agrees closely with the result obtained for the uptake of hydrogen ions per TMV monomer in the spontaneous dimerization.

Coloring Agents↗
PubMed1999

Milestones in the research on tobacco mosaic virus.

Beijerinck's (1898) recognition that the cause of tobacco mosaic disease was a novel kind of pathogen became the breakthrough which eventually led to the establishment of virology as a science. Research on this agent, tobacco mosaic virus (TMV), has continued to be at the forefront of virology for the past century. After an initial phase, in which numerous biological properties of TMV were discovered, its particles were the first shown to consist of RNA and protein, and X-ray diffraction analysis of their structure was the first of a helical nucleoprotein. In the molecular biological phase of research, TMV RNA was the first plant virus genome to be sequenced completely, its genes were found to be expressed by cotranslational particle disassembly and the use of subgenomic mRNA, and the mechanism of assembly of progeny particles from their separate parts was discovered. Molecular genetical and cell biological techniques were then used to clarify the roles and modes of action of the TMV non-structural proteins: the 126 kDa and 183 kDa replicase components and the 30 kDa cell-to-cell movement protein. Three different TMV genes were found to act as avirulence genes, eliciting hypersensitive responses controlled by specific, but different, plant genes. One of these (the N gene) was the first plant gene controlling virus resistance to be isolated and sequenced. In the biotechnological sphere, TMV has found several applications: as the first source of transgene sequences conferring virus resistance, in vaccines consisting of TMV particles genetically engineered to carry foreign epitopes, and in systems for expressing foreign genes. TMV owes much of its popularity as a research mode to the great stability and high yield of its particles. Although modern methods have much decreased the need for such properties, and TMV may have a less dominant role in the future, it continues to occupy a prominent position in both fundamental and applied research.

History, 19th Century↗
PubMed2004

ORF6 of Tobacco mosaic virus is a determinant of viral pathogenicity in Nicotiana benthamiana.

Tobacco mosaic virus (TMV) contains a sixth open reading frame (ORF6) that potentially encodes a 4.8 kDa protein. Elimination of ORF6 from TMV attenuated host responses in Nicotiana benthamiana without alteration in virus accumulation. Furthermore, heterologous expression of TMV ORF6 from either potato virus X (PVX) or tobacco rattle virus (TRV) vectors enhanced the virulence of both viruses in N. benthamiana, also without effects on their accumulation. By contrast, the presence or absence of TMV ORF6 had no effect on host response or virus accumulation in N. tabacum plants infected with TMV or PVX. TMV ORF6 also had no effect on the synergism between TMV and PVX in N. tabacum. However, the presence of the TMV ORF6 did have an effect on the pathogenicity of a TRV vector in N. tabacum. In three different types of assay carried out in N. benthamiana plants, expression of TMV ORF6 failed to suppress gene silencing. Expression in N. benthamiana epidermal cells of the encoded 4.8 kDa protein fused to the green fluorescent protein at either end showed, in addition to widespread cytosolic fluorescence, plasmodesmatal targeting specific to both fusion constructs. The role of the ORF6 in host responses is discussed.

Amino Acid Sequence↗
PubMed2005

Effects of calreticulin on viral cell-to-cell movement.

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.

Amino Acid Sequence↗