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PubMed2005

Cell-to-cell movement of Alfalfa mosaic virus can be mediated by the movement proteins of Ilar-, bromo-, cucumo-, tobamo- and comoviruses and does not require virion formation.

RNA 3 of Alfalfa mosaic virus (AMV) encodes the movement protein (MP) and coat protein (CP). Chimeric RNA 3 with the AMV MP gene replaced by the corresponding MP gene of Prunus necrotic ringspot virus, Brome mosaic virus, Cucumber mosaic virus or Cowpea mosaic virus efficiently moved from cell-to-cell only when the expressed MP was extended at its C-terminus with the C-terminal 44 amino acids of AMV MP. MP of Tobacco mosaic virus supported the movement of the chimeric RNA 3 whether or not the MP was extended with the C-terminal AMV MP sequence. The replacement of the CP gene in RNA 3 by a mutant gene encoding a CP defective in virion formation did not affect cell-to-cell transport of the chimera's with a functional MP. A GST pull-down technique was used to demonstrate for the first time that the C-terminal 44 amino acids of the MP of a virus belonging to the family Bromoviridae interact specifically with AMV virus particles. Together, these results demonstrate that AMV RNA 3 can be transported from cell-to-cell by both tubule-forming and non-tubule-forming MPs if a specific MP-CP interaction occurs.

Alfalfa mosaic virus↗

PubMed2006

Arabidopsis thaliana is an asymptomatic host of Alfalfa mosaic virus.

The susceptibility of Arabidopsis thaliana ecotypes to infection by Alfalfa mosaic virus (AMV) was evaluated. Thirty-nine ecotypes supported both local and systemic infection, 26 ecotypes supported only local infection, and three ecotypes could not be infected. No obvious symptoms characteristic of virus infection developed on the susceptible ecotypes under standard conditions of culture. Parameters of AMV infection were characterized in ecotype Col-0, which supported systemic infection and accumulated higher levels of AMV than the symptomatic host Nicotiana tabacum. The formation of infectious AMV particles in infected Col-0 was confirmed by infectivity assays on a hypersensitive host and by electron microscopy of purified virions. Replication and transcription of AMV was confirmed by de novo synthesis of AMV subgenomic RNA in Col-0 protoplasts transfected with AMV RNA or plasmids harboring AMV cDNAs.

Alfalfa mosaic virus↗

PubMed1999

Expression of alfalfa mosaic virus coat protein in tobacco mosaic virus (TMV) deficient in the production of its native coat protein supports long-distance movement of a chimeric TMV.

Alfalfa mosaic virus (AlMV) coat protein is involved in systemic infection of host plants, and a specific mutation in this gene prevents the virus from moving into the upper uninoculated leaves. The coat protein also is required for different viral functions during early and late infection. To study the role of the coat protein in long-distance movement of AlMV independent of other vital functions during virus infection, we cloned the gene encoding the coat protein of AlMV into a tobacco mosaic virus (TMV)-based vector Av. This vector is deficient in long-distance movement and is limited to locally inoculated leaves because of the lack of native TMV coat protein. Expression of AlMV coat protein, directed by the subgenomic promoter of TMV coat protein in Av, supported systemic infection with the chimeric virus in Nicotiana benthamiana, Nicotiana tabacum MD609, and Spinacia oleracea. The host range of TMV was extended to include spinach as a permissive host. Here we report the alteration of a host range by incorporating genetic determinants from another virus.

Alfalfa mosaic virus↗

PubMed1994

The 3'-untranslated region of alfalfa mosaic virus RNA 3 contains at least two independent binding sites for viral coat protein.

The 3'-termini of the three genomic RNAs of alfalfa mosaic virus contain a common sequence of 145 nucleotides (nt) with a specific binding site for coat protein (CP). This sequence consists of several stem/loop structures interspersed with single-stranded AUGC-motifs; in RNA 3 this folding pattern is extended to a region upstream of the homologous sequence. By band-shift assays a minimum of two specific binding sites for CP were identified near the 3'-end of RNA 3. Site 1 consists of the region between nt 11 and 127 from the 3'-end and contains two AUGC-motifs. Site 2 is located between nt 133 and 208 from the 3'-end in a sequence that is largely unique to RNA 3 and contains also two AUGC-motifs. Deletion studies revealed that the two sites could bind CP independently of each other and permitted the identification of sequence elements that are essential for the activity of each site. By site-directed mutagenesis it was shown that the AUGC-motifs are important for binding of CP to both sites. These binding sites may play a role in the phenomenon that each genomic RNA has to be complexed with a few CP molecules to initiate infection. Later in the replication cycle they may act as origins for the assembly of virus particles.

Alfalfa mosaic virus↗

PubMed1996

Structural elements of the 3'-terminal coat protein binding site in alfalfa mosaic virus RNAs.

The 3'-terminal of the three genomic RNAs of alfalfa mosaic virus (AIMV) and ilarviruses contain a number of AUGC-motifs separated by hairpin structures. Binding of coat protein (CP) to such elements in the RNAs is required to initiate infection of these viruses. Determinants for CP binding in the 3'-terminal 39 nucleotides (nt) of AIMV RNA 3 were analyzed by band-shift assays. From the 5'- to 3'-end this 39 nt sequence contains AUGC-motif 3, stem-loop structure 2 (STLP2), AUGC-motif 2, stem-loop structure 1 (STLP1) and AUGC-motif 1. A mutational analysis showed that all three AUGC-motifs were involved in CP binding. Mutation of the A- and U-residues of motifs 1 or 3 had no effect on CP binding but similar mutations in motif 2 abolished CP binding. A mutational analysis of the stem of STLP1 and STLP2 confirmed the importance of these hairpins for CP binding. Randomization of the sequence of the stems and loops of STLP1 and STLP2 had no effect on CP binding as long as the secondary structure was maintained. This indicates that the two hairpins are not involved in sequence-specific interactions with CP. They may function in a secondary structure-specific interaction with CP and/or in the assembly of the AUGC-motifs in a configuration required for CP binding.

Alfalfa mosaic virus↗

PubMed2001

Role of the alfalfa mosaic virus movement protein and coat protein in virus transport.

The movement protein (MP) and coat protein (CP) encoded by Alfalfa mosaic virus (AMV) RNA 3 are both required for virus transport. RNA 3 vectors that expressed nonfused green fluorescent protein (GFP), MP:GPF fusions, or GFP:CP fusions were used to study the functioning of mutant MP and CP in protoplasts and plants. C-terminal deletions of up to 21 amino acids did not interfere with the function of the CP in cell-to-cell movement, although some of these mutations interfered with virion assembly. Deletion of the N-terminal 11 or C-terminal 45 amino acids did not interfere with the ability of MP to assemble into tubular structures on the protoplast surface. Additionally, N- or C-terminal deletions disrupted tubule formation. A GFP:CP fusion was targeted specifically into tubules consisting of a wild-type MP. All MP deletion mutants that showed cell-to-cell and systemic movement in plants were able to form tubular structures on the surface of protoplasts. Brome mosaic virus (BMV) MP did not support AMV transport. When the C-terminal 48 amino acids were replaced by the C-terminal 44 amino acids of the AMV MP, however, the BMV/AMV chimeric protein permitted wild-type levels of AMV transport. Apparently, the C terminus of the AMV MP, although dispensable for cell-to-cell movement, confers specificity to the transport process.

Alfalfa mosaic virus↗

PubMed2001

Intracellular localization and movement phenotypes of alfalfa mosaic virus movement protein mutants.

Thirteen mutations were introduced in the movement protein (MP) gene of Alfalfa mosaic virus (AMV) fused to the green fluorescent protein (GFP) gene and the mutant MP-GFP fusions were expressed transiently in tobacco protoplasts, tobacco suspension cells, and epidermal cells of tobacco leaves. In addition, the mutations were introduced in the MP gene of AMV RNA 3 and the mutant RNAs were used to infect tobacco plants. Ten mutants were affected in one or more of the following functions of MP: the formation of tubular structures on the surface of protoplasts, association with the endoplasmic reticulum (ER) of suspension cells and epidermal cells, targeting to punctate structures in the cell wall of epidermis cells, movement from transfected cells to adjacent cells in epidermis tissue, cell-to-cell movement, or long-distance movement in plants. The mutations point to functional domains of the MP and support the proposed order of events in AMV transport. Studies with several inhibitors indicate that actin or microtubule components of the cytoskeleton are not involved in tubule formation by AMV MP. Evidence was obtained that tubular structures on the surface of transfected protoplasts contain ER- or plasmalemma-derived material.

Alfalfa mosaic virus↗

PubMed1993

Effect of the alfalfa mosaic virus movement protein expressed in transgenic plants on the permeability of plasmodesmata.

Symplastic transport of different sized fluorescent probes has been assessed in leaf epidermal cells of transgenic Nicotiana plants expressing the movement protein (MP) of alfalfa mosaic virus (AMV). In both N. tabacum and N. benthamiana, the size exclusion limit (SEL) of plasmodesmata increased from M(r) 1000, which represents the commonly accepted limit, to over 4.4K. However, in control plants, movement of a 3K probe was seen in 11 to 22% of the injections, indicating that plasmodesmata may on occasion allow the passage of molecules larger than was previously thought. The increase of SEL due to the presence of the AMV MP, although significant, remains insufficient to permit the passage of viral particles and the possibility of other mechanisms involved in viral cell-to-cell spread is discussed.

Alfalfa mosaic virus↗

PubMed1994

Mapping of the RNA-binding domain of the alfalfa mosaic virus movement protein.

In-frame contiguous deletions were created in the movement protein gene of alfalfa mosaic virus by site-directed mutagenesis. The mutated movement proteins were expressed in Escherichia coli, extracted and then purified by denaturing gel electrophoresis and then renatured. Their binding ability with RNA was assayed by electrophoretic retardation and u.v.-crosslinking. Results indicated that a domain included within amino acids 36 to 81 was necessary for RNA binding.

Alfalfa mosaic virus↗

PubMed1994

Alleged reaction in gel-immunodiffusion of an IgM monoclonal antibody with alfalfa mosaic virus and cucumber mosaic virus is an artefact.

A previously reported spurious serological cross-reaction between alfalfa mosaic virus (AMV) and cucumber mosaic virus (CMV), which had been defined by the reaction in gel-immunodiffusion tests of a single IgM monoclonal antibody (MAb), MAb 8, was no longer detected in the presence of 0.1 M-NaCl. The non-specific reactivity of this IgM was also confirmed in Western blotting assays. When skimmed milk was used as a blocking agent and as a diluent of antibodies, MAb 8 failed to recognize AMV and CMV coat proteins. Hence, it is concluded that the alleged cross-reaction between AMV and CMV is due to non-specific binding of MAb 8 and that there is no evidence for a serological relationship between these two viruses.

Alfalfa mosaic virus↗

PubMed1996

Purification, characterization, assembly and crystallization of assembled alfalfa mosaic virus coat protein expressed in Escherichia coli.

The coast protein of alfalfa mosaic virus (AMV) was cloned and expressed in Escherichia coli as a fusion protein containing a 37 amino acid extension with a (His)6 region for affinity purification. About half of the expressed recombinant coat protein (rCP) was soluble upon extraction and half was insoluble in inclusion bodies. Western blot analysis confirmed the identity of the rCP and protoplast infectivity assays indicated that the rCP was biologically active in an early event of AMV infection, called genome activation. The rCP assembled into T = 1 empty icosahedral particles, as described previously for native coat protein. Empty particles formed hexagonal crystals that diffracted X-rays to 5.5 A resolution. The crystals of trypsin-treated particles of rCP appear to be isomorphous with crystals of trypsin-treated particles of native coat protein, Spherical particles containing RNA assembled when the rCP was combined with in vitro transcripts of AMV RNA4, the smallest naturally encapsidated AMV RNA. Bacilliform particles that resembled native virions assembled when the rCP was combined with transcripts of RNA1, the largest genomic RNA.

Alfalfa mosaic virus↗

PubMed1997

The 3' untranslated region of alfalfa mosaic virus RNA3 contains a core promoter for minus-strand RNA synthesis and an enhancer element.

The 3' untranslated regions (UTRs) of the three genomic RNAs of alfalfa mosaic virus consist of a 3' homologous sequence of 145 nt and upstream unique sequences 18-34 nt in length. Mutations were made in the 3' UTR of a cDNA clone of RNA3. Point mutations in five AUGC motifs which interfere with specific binding of coat protein to the 3' UTR had no effect on template activity of RNA3 for minus-strand RNA synthesis in vitro by purified viral RNA-dependent RNA polymerase (RdRp). Deletion analysis showed that the 3' homologous sequence of 145 nt was sufficient for a low level of template activity in the in vitro RdRp assay and a similarly low level of RNA3 accumulation in plants. The presence of an additional sequence of nucleotides 145-165 from the 3' end of RNA3 enhanced template recognition by RdRp in vitro and accumulation of RNA3 in vivo to wild-type levels.

Alfalfa mosaic virus↗

PubMed1997

Replication of alfalfa mosaic virus RNA 3 with movement and coat protein genes replaced by corresponding genes of Prunus necrotic ringspot ilarvirus.

Alfalfa mosaic virus (AMV) and Prunus necrotic ringspot virus (PNRSV) are tripartite positive-strand RNA plant viruses that encode functionally similar translation products. Although the two viruses are phylogenetically closely related, they infect a very different range of natural hosts. The coat protein (CP) gene, the movement protein (MP) gene or both genes in AMV RNA 3 were replaced by the corresponding genes of PNRSV. The chimeric viruses were tested for heterologous encapsidation, replication in protoplasts from plants transformed with AMV replicase genes P1 and P2 (P12 plants) and for cell-to-cell transport in P12 plants. The chimeric viruses exhibited basic competence for encapsidation and replication in P12 protoplasts and for a low level of cell-to-cell movement in P12 plants. The potential involvement of the MP gene in determining host specificity in ilarviruses is discussed.

Alfalfa mosaic virus↗

PubMed1998

Amino acids of alfalfa mosaic virus coat protein that direct formation of unusually long virus particles.

In contrast to most alfalfa mosaic virus (AMV) strains (YSMV, S, M and 425), AMV strains VRU and 1 5/64 can form abnormally long virus particles, an ability which has been linked to the coat protein (CP). In order to study this phenomenon, the CP-encoding RNAs 3 of AMV strains VRU and 1 5/64 were cloned and fully sequenced. Comparative sequence analyses of AMV RNA 3 sequences derived from different strains revealed two non-conservative amino acid substitutions, Ser65 and Leu175, which occur exclusively in the closely related VRU- and 15/64-CPs. When these amino acid alterations were introduced into the CP of AMV strain 425 unusually long virus particles were assembled. This confirms that amino acids Ser66 and Leu175 of the CPs of AMV strains VRU and 15/64 are involved in the formation of tubular virus particles.

Alfalfa mosaic virus↗

PubMed2000

The complete nucleotide sequence of apple mosaic virus (ApMV) RNA 1 and RNA 2: ApMV is more closely related to alfalfa mosaic virus than to other ilarviruses.

The complete nucleotide sequences of apple mosaic virus RNA 1 and 2 have been characterized. Apple mosaic virus RNA 1 is 3476 nucleotides in length and encodes a single large open reading frame (ORF), whereas apple mosaic virus RNA 2 is 2979 nucleotides in length and also encodes a single ORF. The amino acid sequences encoded by RNA 1 and 2 show similarity to all of the other ilarviruses for which sequence data are available, but both are more closely related to alfalfa mosaic virus (AMV) than to other ilarviruses. Points of similarity include the absence of ORF 2b, present on the RNA 2 of all previously characterized ilarviruses. The close relationship to AMV also occurs in the movement protein, encoded by RNA 3, but not with the coat protein. These data suggest that the present taxonomy should be revised, and that AMV should be considered an aphid-transmissible ilarvirus.

5' Untranslated Regions↗

PubMed2001

RNAs 1 and 2 of Alfalfa mosaic virus, expressed in transgenic plants, start to replicate only after infection of the plants with RNA 3.

RNAs 1 and 2 of the tripartite genome of Alfalfa mosaic virus (AMV) encode the two viral replicase subunits. Full-length DNA copies of RNAs 1 and 2 were used to transform tobacco plants (R12 lines). None of the transgenic lines showed resistance to AMV infection. In healthy R12 plants, the transcripts of the viral cDNAs were copied by the transgenic viral replicase into minus-strand RNAs but subsequent steps in replication were blocked. When the R12 plants were inoculated with AMV RNA 3, this block was lifted and the transgenic RNAs 1 and 2 were amplified by the transgenic replicase together with RNA 3. The transgenic expression of RNAs 1 and 2 largely circumvented the role of coat protein (CP) in the inoculum that is required for infection of nontransgenic plants. The results for the first time demonstrate the role of CP in AMV plus-strand RNA synthesis at the whole plant level.

Alfalfa mosaic virus↗

PubMed2001

Recognition of cis-acting sequences in RNA 3 of Prunus necrotic ringspot virus by the replicase of Alfalfa mosaic virus.

Alfalfa mosaic virus (AMV) and Prunus necrotic ringspot virus (PNRSV) belong to the genera ALFAMOVIRUS: and ILARVIRUS:, respectively, of the family BROMOVIRIDAE: Initiation of infection by AMV and PNRSV requires binding of a few molecules of coat protein (CP) to the 3' termini of the inoculum RNAs and the CPs of the two viruses are interchangeable in this early step of the replication cycle. CIS:-acting sequences in PNRSV RNA 3 that are recognized by the AMV replicase were studied in in vitro replicase assays and by inoculation of AMV-PNRSV RNA 3 chimeras to tobacco plants and protoplasts transformed with the AMV replicase genes (P12 plants). The results showed that the AMV replicase recognized the promoter for minus-strand RNA synthesis in PNRSV RNA 3 but not the promoter for plus-strand RNA synthesis. A chimeric RNA with PNRSV movement protein and CP genes accumulated in tobacco, which is a non-host for PNRSV.

3' Untranslated Regions↗

PubMed2005

Coat protein enhances translational efficiency of Alfalfa mosaic virus RNAs and interacts with the eIF4G component of initiation factor eIF4F.

The three plus-strand genomic RNAs of Alfalfa mosaic virus (AMV) and the subgenomic messenger for viral coat protein (CP) contain a 5'-cap structure, but no 3'-poly(A) tail. Binding of CP to the 3' end of AMV RNAs is required for efficient translation of the viral RNAs and to initiate infection in plant cells. To study the role of CP in translation, plant protoplasts were transfected with luciferase (Luc) transcripts with 3'-terminal sequences consisting of the 3' untranslated region of AMV RNA 3 (Luc-AMV), a poly(A) tail of 50 residues [Luc-poly(A)] or a short vector-derived sequence (Luc-control). Pre-incubation of the transcripts with CP had no effect on Luc expression from Luc-poly(A) or Luc-control, but strongly stimulated Luc expression from Luc-AMV. From time-course experiments, it was calculated that CP binding increased the half-life of Luc-AMV by 20 % and enhanced its translational efficiency by about 40-fold. In addition to the 3' AMV sequence, the cap structure was required for CP-mediated stimulation of Luc-AMV translation. Glutathione S-transferase pull-down assays revealed an interaction between AMV CP and initiation factor complexes eIF4F and eIFiso4F from wheatgerm. Far-Western blotting revealed that this binding occurred through an interaction of CP with the eIF4G and eIFiso4G subunits of eIF4F and eIFiso4F, respectively. The results support the hypothesis that the role of CP in translation of viral RNAs mimics the role of the poly(A)-binding protein in translation of cellular mRNAs.

3' Untranslated Regions↗