The distinct disease phenotypes of the common and yellow vein strains of Tomato golden mosaic virus are determined by nucleotide differences in the 3'-terminal region of the gene encoding the movement protein

Keith Saunders1, Christina Wege2, Karuppannan Veluthambia,1, Holger Jeske2 and John Stanley1

Department of Virus Research, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK1
Universität Stuttgart, Biologisches Institut, Lehrstuhl für Molekularbiologie und Virologie der Pflanzen, Pfaffenwaldring 57, 70550 Stuttgart, Germany2

Author for correspondence: John Stanley. Fax +44 1603 450045. e-mail john.stanley{at}bbsrc.ac.uk


   Abstract
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
In Nicotiana benthamiana, the common strain of the bipartite geminivirus Tomato golden mosaic virus (csTGMV) induces extensive chlorosis whereas the yellow vein strain (yvTGMV) produces veinal chlorosis on systemically infected leaves. In Datura stramonium, csTGMV produces leaf distortion and a severe chlorotic mosaic whereas yvTGMV produces only small chlorotic lesions on systemically infected leaves. Genetic recombination and site-directed mutagenesis studies using infectious clones of csTGMV and yvTGMV have identified a role in symptom production for the gene encoding the movement protein (MP). The MP amino acid at position 272, either valine (csTGMV) or isoleucine (yvTGMV), influenced symptoms in both hosts by inducing an intermediate phenotype when exchanged between the two strains. Exchange of an additional strain-specific MP amino acid at position 288, either glutamine (csTGMV) or lysine (yvTGMV), resulted in the change of symptom phenotype to that of the other strain. In situ hybridization analysis in N. benthamiana demonstrated that there was no qualitative difference in the tissue distribution of the two strains although csTGMV accumulated in higher amounts, suggesting that the efficiency of virus movement rather than distinct differences in tissue specificity of the strains is responsible for the symptom phenotypes.


   Introduction
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
Geminiviruses belong to a diverse family of plant viruses that have small circular single-stranded DNA genomes encapsidated in twinned quasi-isometric particles. Based on their biological and genetic properties four genera are currently recognized (Van Regenmortel et al., 2000 ). The majority of members of the Begomovirus genus have a genome comprising two similar-sized DNA components (DNA A and DNA B). DNA A encodes the coat protein, the replication-associated protein (Rep) which is required for rolling circle replication of the viral DNA, and proteins that participate in the control of replication and gene expression, while DNA B encodes proteins that function in virus movement (reviewed by Bisaro, 1996 ; Sanderfoot & Lazarowitz, 1996 ; Hanley-Bowdoin et al., 1999 ). The movement protein (MP) and nuclear shuttle protein (NSP) encoded by DNA B act in a cooperative manner to facilitate the movement of viral nucleic acid from its site of replication in the nucleus to adjacent cells. NSP has a propensity to localize in the nucleus where it can bind viral ssDNA (Pascal et al., 1994 ). In the presence of MP, NSP (and presumably the viral ssDNA) is redirected from the nucleus to the periphery of the cell (Noueiry et al., 1994 ; Sanderfoot & Lazarowitz, 1995 ). MP additionally increases the plasmodesmal size exclusion limit and has the ability to move between cells, providing a possible mechanism for the movement of viral DNA from cell to cell (Noueiry et al., 1994 ).

Viable pseudorecombinants can often be produced by reassortment of the genomic components of closely related strains of bipartite begomoviruses such as the common strain (cs) and yellow vein strain (yv) of Tomato golden mosaic virus (TGMV). In Nicotiana benthamiana, csTGMV induces extensive chlorosis throughout systemically infected leaves whereas chlorotic symptoms associated with yvTGMV are largely confined to the veins. In D. stramonium, csTGMV produces leaf distortion and a severe chlorotic mosaic whereas yvTGMV produces small chlorotic lesions on systemically infected leaves (von Arnim & Stanley, 1992 ). Infectivity studies using csTGMV and yvTGMV pseudorecombinants have demonstrated that their distinct symptoms segregate with the DNA B genomic component. The construction of DNA B recombinants between these strains enabled the phenotypic difference to be attributed to a genomic fragment encompassing the MP gene and part of the intergenic region (von Arnim & Stanley, 1992 ).

In the present study we have used additional DNA B recombinants and mutants to map symptom phenotype differences of csTGMV and yvTGMV to specific changes within the carboxy-terminal region of the MP gene. In addition, in situ localization studies have been used to investigate the relationship between symptom phenotype and tissue distribution of these two TGMV strains.


   Methods
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
{blacksquare} Construction of DNA B recombinants.
The construction of infectious cloned copies of the csTGMV genome (clones csTA and csTB) and yvTGMV DNA B (yvTBE) has been described (von Arnim & Stanley, 1992 ). To facilitate the construction of DNA B recombinants and for site-directed mutagenesis, DNA B inserts were subcloned into the EcoRI site of M13mp18. Homologous DNA fragments were exchanged between the DNA B components of the two strains using common restriction sites, as outlined in Fig. 1. The identity of recombinant clones was verified by PstI restriction endonuclease digestion (von Arnim & Stanley, 1992 ) and by sequence analysis using a T7 sequencing kit (Pharmacia).



View larger version (18K):
[in this window]
[in a new window]
 
Fig. 1. Recombinants produced in vitro between csTGMV and yvTGMV DNA B components. Recombinant DNA B components generated by exchange of fragments between csTGMV (filled box) and yvTGMV (open box) are shown below a map of TGMV DNA B giving the location of restriction sites used to create the recombinants. Symptom phenotypes produced by the recombinants are indicated at the right.

 
{blacksquare} Site-directed mutagenesis.
The nucleotide sequence of yvTGMV (Hamilton et al., 1984 ) as modified by MacDowell et al. (1986) , and that of csTGMV (von Arnim & Stanley, 1992 ), were used to design oligonucleotide primers for site-directed mutagenesis using a Bio-Rad Muta-Gene kit. Nucleotide numbering has been modified according to current convention, beginning immediately after the putative nick site within the TAATATT{downarrow}AC motif located within the intergenic region. Mutations introduced into the MP gene are shown in Fig. 2. Nucleotide 2038 of csTGMV DNA B was changed from A to G to introduce an NsiI site in the same relative position to that found in yvTGMV, producing clone csTBN. Nucleotide 1296 of csTGMV DNA B was changed from T to C, as found in yvTGMV, without altering the MP amino acid at position 258 (glutamine in both strains), producing clone cs(yv258). Nucleotide 1277 of csTGMV DNA B was changed from T to A, altering the MP amino acid at position 265 from methionine to leucine in clone cs(yv265). In the reciprocal construct, the nucleotide at the same position in yvTGMV DNA B was changed from A to T, altering the MP amino acid at position 265 from leucine to methionine in clone yv(cs265). Nucleotide 1256 of csTGMV DNA B was changed from C to T, altering the MP amino acid at position 272 from valine to isoleucine in clone cs(yv272). In the reciprocal construct, the nucleotide at the same position in yvTGMV DNA B was changed from T to C, altering the MP amino acid at position 272 from isoleucine to valine in clone yv(cs272). Nucleotide 1208 of yvTGMV DNA B was changed from T to G, altering the MP amino acid at position 288 from lysine to glutamine in clone yv(cs288). Using these clones as templates, mutations were made at a second position to produce clones cs(yv265/288), yv(cs265/288), cs(yv272/288) and yv(cs272/288). The integrity of the mutants was confirmed by sequence analysis using a T7 DNA sequencing kit (Pharmacia).



View larger version (15K):
[in this window]
[in a new window]
 
Fig. 2. MP gene sequence variation between csTGMV and yvTGMV strains. The complementary-sense nucleotide sequence and MP amino acid sequence between the NsiI and AflII sites (underlined) of csTGMV are shown. Amino acids and nucleotides that differ in yvTGMV are shown in bold above and below the csTGMV sequences, respectively.

 
{blacksquare} Construction of partial repeats of genomic components.
Clone csTA0.65 was produced by removal of the BamHI(1218)–EcoRI(2113) fragment of the TGMV DNA A clone csTA (von Arnim & Stanley, 1992 ) by digestion with BamHI, which also cuts within the polylinker. Full-length csTGMV DNA A excised from csTA was inserted into the now unique EcoRI site to produce csTA1.65. Partial repeats of DNA B clones cs(yv272) and yv(cs272) were constructed by first subcloning each full-length insert into the EcoRI site of pIC19H (Marsh et al., 1984 ). The 1·2 kbp EcoRI(511)–BglII(1768) fragments were removed from these clones by digestion with BglII, which also cuts within the polylinker, to produce 0.5cs(yv272) and 0.5yv(cs272). The full-length insert of each mutant was then inserted in the EcoRI site of the appropriate clone to produce 1.5cs(yv272) and 1.5yv(cs272), respectively.

{blacksquare} Maintenance and inoculation of plants.
TGMV-infected plants were maintained in an insect-free glasshouse at 25 °C with a photoperiod of 16 h. Plasmids and M13 RF DNA were purified using Qiagen anion exchange columns according to the manufacturer’s protocol. Either 1 µg of the partial repeats of DNA A (csTA1.6) and DNA B [1.5cs(yv272) and 1.5yv(cs272)] or 5 µg of the inserts of the other DNA B recombinants released by EcoRI digestion were inoculated onto celite-dusted N. benthamiana leaves. D. stramonium was inoculated with sap prepared from symptomatic N. benthamiana infected using cloned genomic components.

{blacksquare} Preparation of plant tissue sections.
Leaf explants were immersed in AFE (70% ethanol–37% formaldehyde–glacial acetic acid; 90:5:5) for 1 min at 0 °C, fixed in 6% formaldehyde in PBS containing 10 mM EDTA, dehydrated and embedded in Paraplast Plus (Monoject Scientific Inc.) as described by Jackson (1992) . Alternatively, samples were dehydrated with tetrahydrofuran as described by Romeis (1989) prior to infiltration with THF–Paraplast Plus (1:1) and embedding.

{blacksquare} In situ hybridization.
Sections were prepared as described by Horns & Jeske (1991) . The full-length TGMV DNA A insert of csTA (von Arnim & Stanley, 1992 ) was isolated and labelled by nick-translation (BRL kit no. 8160SB) incorporating biotin-14-dATP (Gibco/BRL). Unincorporated nucleotides were removed using Qiagen tip-5 anion exchange columns. In situ hybridization procedures were carried out as described by Bradley et al. (1993) . Biotinylated probes were detected either with fluorescent streptavidin–FITC (Gibco-BRL) or with streptavidin–alkaline phosphatase (Boehringer) using procedures described by the appropriate manufacturer. Specimens were observed with Leitz Dialux-20 and Zeiss Axioskop epifluorescence microscopes. To enhance contrast of plant tissues, either differential interference contrast or Astrablue counterstain (Gerlach, 1984 ) was used. Photographs were taken on Kodak Ektachrome 50 and 64 (tungsten) films with Wild-MPS45+51 or Zeiss MC 100 spot photoequipment.


   Results
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
Mapping the TGMV strain-specific phenotype
The cloned viral genomes of csTGMV and yvTGMV produce marked phenotypic differences when inoculated onto N. benthamiana and D. stramonium. Previous studies have shown that the phenotypic determinant maps to the DNA B MP gene and part of the intergenic region (von Arnim & Stanley, 1992 ). To precisely locate the sequences responsible for the unique phenotypes, a number of additional fragment exchanges between the DNA B components of both strains were made (Fig. 1). Recombinant DNA B components were inoculated onto N. benthamiana in the presence of csTGMV DNA A (the DNA A component does not contribute to the symptom phenotype; von Arnim & Stanley, 1992 ), and the results are summarized in Table 1. The introduction of an NsiI site at nucleotide 2038 in csTBN, to facilitate some of these exchanges, had no effect on the strain phenotype (data not shown). Exchange of NsiI(1380)–NsiI(2036) fragments in recombinants yv-cs(NsiI–NsiI) and cs-yv(NsiI–NsiI) had no effect on symptoms. However, exchange of HpaI(83)–NcoI(1719) fragments in recombinants yv-cs(HpaI–NcoI) and cs-yv(HpaI–NcoI) altered the phenotype to that of the other strain. As it was previously demonstrated that the HpaI(83)–AflII(1125) fragment does not contribute to the unique phenotypes (von Arnim & Stanley, 1992 ), these results implicate sequences within the AflII(1125)–NsiI(1380) fragment in symptom determination. The change of phenotype brought about by exchanging AflII(1125)–NcoI(1719) fragments in recombinants cs-yv(AflII–NcoI) and yv-cs(AflII–NcoI), and the maintenance of the phenotype in recombinant cs-yv(NsiI–NcoI), containing the yvTGMV NsiI(1380)–NcoI(1719) fragment in a csTGMV background, are both consistent with this conclusion. The contribution of sequences within the AflII(1125)–NsiI(1380) fragment was confirmed using recombinant cs-yv(AflII–NsiI), which induced symptoms typical of yvTGMV. Throughout these experiments, all recombinants produced symptoms typical of either csTGMV or yvTGMV and not an intermediate phenotype, and the phenotypes of selected recombinants were maintained when virus was sap-transmitted to N. benthamiana and D. stramonium (Table 1).


View this table:
[in this window]
[in a new window]
 
Table 1. Infectivity and symptom phenotype of DNA B recombinants

 
Identification of nucleotide differences responsible for the strain-specific phenotype
Inspection of the nucleotide sequences revealed four nucleotide differences between csTGMV and yvTGMV strain in the AflII–NsiI fragment, of which three result in amino acid differences within the MP (Fig. 2). To precisely map the strain phenotype determinants within the fragment, the unique nucleotides were changed, either singly or in pairs, to those found in the other strain, and the effect of these modifications on symptom phenotype was screened in N. benthamiana and D. stramonium (Table 2). D. stramonium was a particularly useful host in these experiments as the symptoms induced by each strain are more distinct than in N. benthamiana (von Arnim & Stanley, 1992 ) although the low infectivity of cloned DNA in this host when introduced by mechanical means necessitated sap transmission of the virus. Alteration of the nucleotide at position 1296 from A (csTGMV) to G (yvTGMV) in mutant cs(yv258) does not alter the encoded amino acid and had no effect on the symptom phenotype. Similarly, exchange of the unique nucleotides at position 1277 (A in csTGMV and T in yvTGMV) in mutants cs(yv265) and yv(cs265), and alteration of the nucleotide at position 1208 from A (yvTGMV) to C (csTGMV) in mutant yv(cs288) had no effect on symptoms, although the modifications altered the encoded amino acids. Also, symptoms remained unaffected when double mutations were introduced at these positions in mutants cs(yv265/288) and yv(cs265/288). In contrast, and contrary to all previous observations, exchange of the unique nucleotides at position 1256 (G in csTGMV and A in yvTGMV) in mutants cs(yv272) and yv(cs272) produced an intermediate phenotype, not only in N. benthamiana, but also in the more discriminating host D. stramonium. Modification of a second nucleotide at position 1208 in mutants cs(yv272/288) and yv(cs272/288) served to completely change the strain phenotype in both hosts. The results demonstrate that the nucleotide at position 1256 contributes significantly to symptom development, although additional modification is necessary to confer a specific strain phenotype. We have demonstrated that modification of the nucleotide at position 1208 is sufficient to satisfy this requirement, although we have not yet eliminated the possibility that modifications elsewhere, for example at positions 1277 and 1296, could be equally as effective. The nucleotide difference at position 1256 alters the encoded amino acid from valine in csTGMV to isoleucine in yvTGMV, and that at position 1208 alters the encoded amino acid from glutamine in csTGMV to lysine in yvTGMV.


View this table:
[in this window]
[in a new window]
 
Table 2. Infectivity and symptom phenotype of DNA B site-directed mutants

 
Investigation of TGMV tissue localization by in situ hybridization
The tissue distribution of csTGMV and yvTGMV in N. benthamiana was examined by in situ hybridization to ascertain whether differences could account for the distinct phenotypes associated with the two strains (representative sections are shown in Fig. 3). As a consequence of viral infection, symptomatic leaves (panels B and C) displayed a perturbed morphology in comparison with a healthy leaf (panel A). Infected cells were readily identified in these sections by the intense staining of their nuclei, and no obvious difference in tissue distribution was observed between csTGMV and yvTGMV. Both strains were associated with phloem cells in which they occurred at a similar frequency, and both subsequently moved to adjacent tissues, including mesophyll and epidermal cells and occasionally trichomes during the course of infection. However, a comparative analysis of ~500 sections prepared from 20 individual leaves of infected plants harvested at similar time-points in two independent experiments indicated that the progression of infection to tissues external to the phloem was slower for yvTGMV than for csTGMV.



View larger version (70K):
[in this window]
[in a new window]
 
Fig. 3. In situ localization of csTGMV and yvTGMV in N. benthamiana leaves. Longitudinal sections from a healthy leaf (A) and from leaves infected with csTGMV (B) and yvTGMV (C) are shown. All sections were hybridized with biotin-labelled full-length TGMV DNA. Infected nuclei are stained black. Bar represents 50 µm.

 

   Discussion
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
Previously, using infectious pseudorecombinants, we demonstrated that the DNA B components of csTGMV and yvTGMV are responsible for induction of the distinct symptoms associated with these naturally occurring virus strains (von Arnim & Stanley, 1992 ). Additionally, recombinant DNA B components produced in vitro were used to map the phenotypic differences to the MP gene and part of the intergenic region. The importance of the movement protein as a key pathogenicity factor was demonstrated by constitutively expressing MP of Squash leaf curl virus (SqLCV) in N. benthamiana (Pascal et al., 1993 ) and MP of Tomato mottle virus (TMoV) in N. tabacum (Duan et al., 1997 ), in which they induced phenotypes reminiscent of the wild-type virus disease symptoms. Spontaneous mutations in TMoV MP during transformation produced less pronounced phenotypes, and a deletion mutant truncated by approximately one third at its carboxy terminus was associated with normal plants (Duan et al., 1997 ), implying that the protein itself was responsible for the phenotype. In the present investigation we have mapped the phenotypic differences between csTGMV and yvTGMV to an AflII–NsiI fragment encompassing the MP gene carboxy-terminal region. The strains differ by only four nucleotides within this region, and site-directed mutagenesis demonstrated that nucleotide 1256, responsible for an amino acid change of valine in csTGMV to isoleucine in yvTGMV, contributed significantly to the symptom phenotype. However, altering the nucleotide at this position to that found in the other strain did not completely change the phenotype but instead induced an intermediate symptom. To completely alter the phenotype an additional nucleotide modification at position 1208 was required, that alone had no apparent effect on symptom development.

In situ hybridization studies have demonstrated that Abutilon mosaic virus (AbMV) is confined to the phloem in Abutilon sellovianum. Even so, AbMV induces striking chlorotic mosaic predominantly in palisade and spongy parenchyma tissues (Horns & Jeske, 1991 ), a phenomenon which has been attributed to virus-induced disruption of phloem transport resulting in down-regulation of photosynthetically active cells (Jeske & Werz, 1978 ). Similarly, dysfunction of infected phloem tissues may contribute to the extent of chlorosis associated with csTGMV and yvTGMV strains. However, in situ localization studies demonstrate that csTGMV and yvTGMV exhibit similar tissue distribution characteristics. In contrast to AbMV, neither strain is phloem-limited, both being able to infect mesophyll and epidermal cells. This is consistent with, and extends observations on, the distribution of TGMV pathogenic effects in N. benthamiana (Rushing et al., 1987 ), and immunolocalization studies on TGMV Rep and replication enhancer protein (Nagar et al., 1995 ) and on coat protein of Bean dwarf mosaic virus (Wang et al., 1996 ) in this host. This suggests that the distinct strain phenotypes are determined by a quantitative effect, dictated by either the rate of movement of the infection into the newly developing leaves or the efficiency of virus replication in these tissues. Our finding that the symptom differences map to the MP gene suggests that cell-to-cell movement of the virus is compromised for yvTGMV.

At this time, we are unable to distinguish between an effect at the nucleotide or amino acid level. Thus, we cannot rule out the possibility that the level of expression of the MP gene may be affected by the nucleotide changes at the 3’ terminus of the gene. Alternatively, the strain-specific amino acids at position 272, valine or isoleucine, may influence MP function, although it is remarkable that such closely related amino acids with similar non-polar aliphatic side groups should have such a marked effect on symptom development. If this is the case, however, clearly a second mutation, such as occurs at position 288 (either glutamine or lysine), is required to exacerbate the effect and completely alter the phenotype. It is conceivable that slight alterations to the protein structure brought about by these changes could affect MP function, for example the efficiency with which it interacts with either NSP during subcellular protein targeting (Sanderfoot & Lazarowitz, 1995 ; Sanderfoot et al., 1996 ) or host factors during cell-to-cell movement of the viral DNA (Noueiry et al., 1994 ; Ward et al., 1997 ).

Studies on mutants generated in vitro have identified regions within MP that are essential for virus infectivity (Ingham et al., 1995 ; Haley et al., 1995 ) and functional domains have been mapped to some extent in SqLCV MP, although there are relatively few examples of mutations being introduced in vitro into the region equivalent to the TGMV DNA B NsiI–AflII fragment. Deletion of isoleucine at position 280 and concomitant alteration of cysteine to phenylalanine in SqLCV MP had no effect on symptom phenotype, although modification of asparagine to alanine at position 260 altered MP subcellular location and prevented NSP relocalization (Sanderfoot & Lazarowitz, 1995 ), resulting in delayed and attenuated symptoms (Ingham et al., 1995 ). The modifications that we have identified as being important to symptom development in csTGMV and yvTGMV occur at other positions within the MP gene carboxy-terminal region. Thus, our results on naturally occurring TGMV variants complement previous observations on begomovirus MP mutants, and serve to emphasize a role for this protein in symptom development.


   Acknowledgments
 
K.S. and J.S. were funded by the Biotechnology and Biological Sciences Research Council, and C.W. and H.J. were funded by the Hans-Böckler-Stiftung and the Bundesminister für Forschung und Technologie (grant BCT 507). K.V. received a British Government Technical Cooperation Training Award. TGMV was maintained and manipulated with the authority of the Ministry of Agriculture, Fisheries and Food under the Plant Health (Great Britain) Order 1993, licences PHF 1419C/1922(5/96) and PHF 1419C/1907(6/96).


   Footnotes
 
a Present address: Department of Biotechnology, School of Biological Sciences, Madurai Kamaraj University, Madurai 625021, India.


   References
Top
Abstract
Introduction
Methods
Results
Discussion
References
 
Bisaro, D. M.(1996). Geminivirus DNA replication. In DNA Replication in Eukaryotic Cells , pp. 833-854. Edited by M. DePamphilis. Cold Spring Harbor, NY:Cold Spring Harbor Laboratory.

Bradley, D., Carpenter, R., Sommer, H., Hartley, N. & Coen, E.(1993). Complementary floral homeotic phenotypes result from opposite orientations of a transposon at the plena locus of Antirrhinum. Cell 72, 85-95.[Medline]

Duan, Y.-P., Powell, C. A., Purcifull, D. E., Broglio, P. & Hiebert, E.(1997). Phenotypic variation in transgenic tobacco expressing mutated geminivirus movement/pathogenicity (BC1) proteins. Molecular Plant–Microbe Interactions 10, 1065-1074.

Gerlach, D. (1984). In Botanische Mikrotechnik, 3rd edn, pp. 128–129. Stuttgart & New York: Georg Thieme Verlag.

Haley, A., Richardson, K., Zhan, X. & Morris, B.(1995). Mutagenesis of the BC1 and BV1 genes of African cassava mosaic virus identifies conserved amino acids that are essential for spread. Journal of General Virology 76, 1291-1298.[Abstract]

Hamilton, W. D. O., Bisaro, D. M., Coutts, R. H. A. & Buck, K. W.(1984). Complete nucleotide sequence of the infectious cloned DNA components of tomato golden mosaic virus: potential coding regions and regulatory sequences. EMBO Journal 3, 2197-2205.

Hanley-Bowdoin, L., Settlage, S. B., Orozco, B. M., Nagar, S. & Robertson, D.(1999). Geminiviruses: models for replication, transcription, and cell cycle regulation. Critical Reviews in Plant Sciences 18, 71-106.

Horns, T. & Jeske, H.(1991). Localization of abutilon mosaic virus (AbMV) DNA within leaf tissue by in situ hybridization. Virology 181, 580-588.[Medline]

Ingham, D. J., Pascal, E. & Lazarowitz, S. G.(1995). Both bipartite geminivirus movement proteins define viral host range, but only BL1 determines viral pathogenicity. Virology 207, 191-204.[Medline]

Jackson, D.(1992). In situ hybridization in plants. In Molecular Plant Pathology: A Practical Approach, vol. 1 , pp. 163-174. Edited by S. J. Gurr, M. J. McPherson& D. J. Bowles. Oxford:Oxford University Press.

Jeske, H. & Werz, G.(1978). The influence of light intensity on pigment composition and ultrastructure of plastids in leaves of diseased Abutilon sellowianum Reg. Phytopathologische Zeitschrift 91, 1-13.

MacDowell, S. W., Coutts, R. H. A. & Buck, K. W.(1986). Molecular characterisation of subgenomic single-stranded and double-stranded DNA forms isolated from plants infected with tomato golden mosaic virus. Nucleic Acids Research 14, 7967-7984.[Abstract]

Marsh, J. L., Erfle, M. & Wykes, E. J.(1984). The pIC plasmid and phage vectors with versatile cloning sites for recombinant selection by insertional inactivation. Gene 32, 481-485.[Medline]

Nagar, S., Pedersen, T. J., Carrick, K. M., Hanley-Bowdoin, L. & Robertson, D.(1995). A geminivirus induces expression of a host DNA synthesis protein in terminally differentiated plant cells. Plant Cell 7, 705-719.[Abstract/Free Full Text]

Noueiry, A. O., Lucas, W. J. & Gilbertson, R. L.(1994). Two proteins of a plant DNA virus coordinate nuclear and plasmodesmal transport. Cell 76, 925-932.[Medline]

Pascal, E., Goodlove, P. E., Wu, L. C. & Lazarowitz, S. G.(1993). Transgenic tobacco plants expressing the geminivirus BL1 protein exhibit symptoms of viral disease. Plant Cell 5, 795-807.[Abstract/Free Full Text]

Pascal, E., Sanderfoot, A. A., Ward, B. M., Medville, R., Turgeon, R. & Lazarowitz, S. G.(1994). The geminivirus BR1 movement protein binds single-stranded DNA and localizes to the cell nucleus. Plant Cell 6, 995-1006.[Abstract/Free Full Text]

Romeis, B. (1989). Mikroskopische Technik, 17th edn, pp. 113–130. Edited by P. Böck. Munich, Vienna & Baltimore: Urban und Schwarzenberg.

Rushing, A. E., Sunter, G., Gardiner, W. E., Dute, R. R. & Bisaro, D. M.(1987). Ultrastructural aspects of tomato golden mosaic virus infection in tobacco. Phytopathology 77, 1231-1236.

Sanderfoot, A. A. & Lazarowitz, S. G.(1995). Cooperation in viral movement: the geminivirus BL1 movement protein interacts with BR1 and redirects it from the nucleus to the cell periphery. Plant Cell 7, 1185-1194.[Abstract/Free Full Text]

Sanderfoot, A. A. & Lazarowitz, S. G.(1996). Getting it together in plant virus movement: cooperative interactions between bipartite geminivirus movement proteins. Trends in Cell Biology 6, 353-358.

Sanderfoot, A. A., Ingham, D. J. & Lazarowitz, S. G.(1996). A viral movement protein as a nuclear shuttle: the geminivirus BR1 movement protein contains domains essential for interaction with BL1 and nuclear localization. Plant Physiology 110, 23-33.[Abstract/Free Full Text]

Van Regenmortel, M. H. V., Fauquet, C. M., Bishop, D. H. L., Carstens, E. B., Estes, M. K., Lemon, S. M., McGeoch, D. J., Maniloff, J., Mayo, M. A., Pringle, C. R. & Wickner, R. B. (editors) (2000). Virus Taxonomy: Classification and Nomenclature of Viruses. Seventh Report of the International Committee on Taxonomy of Viruses. San Diego: Academic Press.

von Arnim, A. & Stanley, J.(1992). Determinants of tomato golden mosaic virus symptom development located on DNA B. Virology 186, 286-293.[Medline]

Wang, H. L., Gilbertson, R. L. & Lucas, W. J.(1996). Spatial and temporal distribution of bean dwarf mosaic geminivirus in Phaseolus vulgaris and Nicotiana benthamiana. Phytopathology 86, 1204-1214.

Ward, B. M., Medville, R., Lazarowitz, S. G. & Turgeon, R.(1997). The geminivirus BL1 movement protein is associated with endoplasmic reticulum-derived tubules in developing phloem cells. Journal of Virology 71, 3726-3733.[Abstract]

Received 11 July 2000; accepted 16 October 2000.



This Article
Abstract
Full Text (PDF)
Alert me when this article is cited
Alert me if a correction is posted
Citation Map
Services
Email this article to a friend
Similar articles in this journal
Similar articles in PubMed
Alert me to new issues of the journal
Download to citation manager
Google Scholar
Articles by Saunders, K.
Articles by Stanley, J.
Articles citing this Article
PubMed
PubMed Citation
Articles by Saunders, K.
Articles by Stanley, J.
Agricola
Articles by Saunders, K.
Articles by Stanley, J.


HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
INT J SYST EVOL MICROBIOL MICROBIOLOGY J GEN VIROL
J MED MICROBIOL ALL SGM JOURNALS