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At least 19 recordsLinked to original sources
PubMed1999

A nanovirus-like DNA component associated with yellow vein disease of Ageratum conyzoides: evidence for interfamilial recombination between plant DNA viruses.

Yellow vein disease of Ageratum conyzoides, a weed species that is widely distributed throughout Asia, has been attributed to infection by the geminivirus Ageratum yellow vein virus (AYVV). In addition to a single AYVV genomic component (DNA A), we have previously demonstrated that infected plants contain chimeric defective viral components, comprising DNA A and nongeminiviral sequences, that act as defective interfering DNAs. A database search has revealed that the nongeminiviral sequences of one such defective component (def19) show significant homology with sequences of nanovirus components that encode replication-associated proteins (Reps). Primers designed to hybridise to the nongeminiviral DNA were used to PCR-amplify a full-length nanovirus-like component, referred to as DNA 1, from an extract of infected A. conyzoides. DNA 1 is unrelated to AYVV DNA A but resembles nanovirus components that encode Reps and is most closely related (73% identity) to a nanovirus-like DNA recently isolated from geminivirus-infected cotton. DNA 1 is dependent on AYVV DNA A for systemic infection of A. conyzoides and Nicotiana benthamiana and can systemically infect N. benthamiana in the presence of the bipartite geminivirus African cassava mosaic virus. A. conyzoides plants coinfected with AYVV DNA A and DNA 1 remain asymptomatic, indicating that additional factors are required to elicit yellow vein disease. Our results provide direct evidence for recombination between distinct families of plant single-stranded DNA viruses and suggest that coinfection by geminivirus and nanovirus-like pathogens may be a widespread phenomenon. The ability of plant DNA viruses to recombine in this way may greatly increase their scope for diversification.

Amino Acid Sequence↗
PubMed2002

In planta protein-protein interactions assessed using a nanovirus-based replication and expression system.

The multipartite genome of the nanovirus Faba bean necrotic yellows virus, which consists of one gene on each DNA component, was exploited to construct a series of virus-based episomal vectors designed for transient replication and gene expression in plants. This nanovirus based expression system yields high levels of protein which allows isolation of recombinant protein and protein complexes from plant tissues. As examples, we demonstrated in planta interaction between the nanovirus F-box protein Clink and SKP1, a constituent of the ubiquitin-dependent protein turnover pathway. Thus, replicative nanovirus vectors provide a simple and efficient means for in planta characterization of protein-protein interaction.

Cell Cycle Proteins↗
PubMed2002

Adaptation from whitefly to leafhopper transmission of an autonomously replicating nanovirus-like DNA component associated with ageratum yellow vein disease.

Ageratum yellow vein disease is caused by the whitefly-transmitted monopartite begomovirus Ageratum yellow vein virus and a DNA beta satellite component. Naturally occurring symptomatic plants also contain an autonomously replicating nanovirus-like DNA 1 component that relies on the begomovirus and DNA beta for systemic spread and whitefly transmission but is not required for maintenance of the disease. Here, we show that systemic movement of DNA 1 occurs in Nicotiana benthamiana when co-inoculated with the bipartite begomovirus Tomato golden mosaic virus and the curtovirus Beet curly top virus (BCTV), but not with the mastrevirus Bean yellow dwarf virus. BCTV also mediates the systemic movement of DNA 1 in sugar beet, and the nanovirus-like component is transmitted between plants by the BCTV leafhopper vector Circulifer tenellus. We also describe a second nanovirus-like component, referred to as DNA 2, that has only 47% nucleotide sequence identity with DNA 1. The diversity and adaptation of nanovirus components are discussed.

Adaptation, Physiological↗
PubMed2000

The master rep concept in nanovirus replication: identification of missing genome components and potential for natural genetic reassortment.

Faba bean necrotic yellows virus (FBYNV), Milk vetch dwarf virus (MDV), and Subterranean clover stunt virus (SCSV) are nanoviruses that infect leguminous plants. From MDV- and SCSV-infected tissue we identified viral DNAs that encode a replication initiator protein (Rep), essential for replication of the multiple circular single-stranded DNAs of these viruses. These previously undescribed Rep proteins of MDV and SCSV are strikingly similar in sequence and functionally equivalent to the master Rep protein of FBYNV. Moreover, we demonstrated that the master Rep proteins of the three viruses are able to trigger replication of heterologous nanovirus DNAs. Such cross-species replication may reflect a considerable potential for genetic reassortment among nanoviruses in nature and be of significance for their evolution.

Amino Acid Sequence↗
PubMed2004

Birth-and-death evolution of protein-coding regions and concerted evolution of non-coding regions in the multi-component genomes of nanoviruses.

Genomes of the four plant viruses of the genus Nanovirus consist of multiple circular single-stranded DNA components, each of which encodes a single protein. Protein phylogenies supported the hypothesis that faba bean necrotic yellows virus (FBNYV) and milk vetch disease virus (MDV) are sister taxa; that subterranean clover stunt virus (SCSV) branched next; and that banana bunchy top virus (BBTV) is an outgroup to the three other species. The phylogeny of replication (Rep) proteins indicate that this small viral multi-gene family has evolved by a process of duplication and subsequent loss of Rep-encoding genome components, analogous to the "birth-and-death" process of evolution which has been described in eukaryotic multi-gene families. By contrast, repeated recombinational events between components were found to have homogenized the non-coding portions of several components encoding unrelated components. For example, as result of recent recombination a portion of the non-coding region is virtually identical among SCSV components 1, 3, 4, 5, and 7. Thus, there is a process of concerted evolution of non-coding regions of Nanovirus genome components, which raises the possibility that certain non-coding regions are subject to functional constraint.

Base Sequence↗
PubMed2002

Characterisation of Rep-encoding components associated with banana bunchy top nanovirus in Vietnam.

We have analysed the sequence variability of the banana bunchy top nanovirus (BBTV) DNA-1 sequence from 17 isolates collected throughout Vietnam, and showed that the level of DNA-1 sequence variation within Vietnam was approximately double that previously reported for Asian BBTV isolates. Furthermore, the sequences separated into two geographical subgroups that generally correlated to the northern or southern regions of Vietnam. We have also characterised an additional putative Rep-encoding component associated with some BBTV isolates from Vietnam. This component, which we have named BBTV-S3, shared 47%, 69%, 56% and 65% nucleotide sequence identity with the previously reported Rep-encoding components BBTV DNA-1, S1, S2 and Y1 respectively.

Amino Acid Sequence↗
PubMed2004

Nanoviruses: genome organisation and protein function.

Nanoviruses, single-stranded DNA (ssDNA) plant viruses with a multipartite genome, share similarities with members of the Circoviridae family that infect mammals or birds as well as with the Geminiviridae, the only other plant virus family with circular ssDNA genomes. Although the virions of the latter are unique and different from that of the circoviruses, the mode of replication of viruses with monopartite or multipartite circular ssDNA genomes is strikingly similar. They multiply by rolling circle replication using virus-encoded multifunctional replication initiator proteins (Rep proteins) that catalyse initiation of ssDNA replication and resolution of replicative ssDNA into circular single-stranded virion DNA. All these ssDNA viruses exploit host polymerases for DNA synthesis and code for proteins that modulate the host's cell cycle favourably for virus multiplication. Recent three-dimensional structure analyses of a geminivirus and a parvovirus Rep protein have revealed an intriguing similarity between the catalytic domains of their respective Rep proteins. Furthermore, these structural data revealed that ssDNA virus replication initiator proteins might represent evolutionary intermediates between certain RNA-binding proteins and some multifunctional origin-binding proteins of papovaviruses.

Amino Acid Motifs↗
PubMed2005

Interaction between a nanovirus-like component and the Tobacco curly shoot virus/satellite complex.

The biological role of DNA1, a nanovirus-like component shown to be associated with the begomovirus/satellite complex, has not yet been identified. Here, we demonstrated that DNA1 of Tobacco curly shoot virus isolate Y35 (TbCSV-Y35) attenuated leaf-curling symptoms induced by TbCSV-Y35 or TbCSV-Y35 plus Y35 DNAbeta in the early stage of symptom development and induced leaf cluster at a later stage of symptom development in Nicotiana benthamiana plants. The leaf disc assay demonstrated that TbCSV-Y35 DNA1 replicated autonomously. Southern blot analysis revealed that TbCSV-Y35 DNA1 reduced viral DNA accumulation. Viral DNA accumulation was not reduced when plants were co-inoculated with TbCSV-Y35 DNAbeta, but the TbCSV-Y35 DNAbeta level was dramatically reduced in the presence of TbCSV-Y35 DNA1. To determine whether the interaction between TbCSV/satellite complex and DNA1 had isolate specificity, DNA1 of TbCSV isolate Y132 was cloned and sequenced. It was found to have 75% nucleotide sequence identity with TbCSV-Y35 DNA1. Infectivity tests showed that TbCSV-Y132 DNA1 had no effect on the symptoms induced by TbCSV-Y35 or TbCSV-Y35 and Y35 DNAbeta in N. benthamiana plants, although Y132 DNA1 could replicate in these plants.

Blotting, Southern↗
PubMed2006

Infectivity of nanovirus DNAs: induction of disease by cloned genome components of Faba bean necrotic yellows virus.

Circumstantial evidence suggests that the genome of Faba bean necrotic yellows virus (FBNYV), a nanovirus, consists of eight distinct, circular, single-stranded DNAs, each of about 1 kb and encoding only one protein. Here, the use of cloned full-length FBNYV DNAs for reproducing FBNYV-like symptoms in Vicia faba, the principal natural host of FBNYV, is reported. Characteristic symptoms of FBNYV infection were obtained in faba bean plants following biolistic DNA delivery or agroinoculation with all eight FBNYV DNAs. Although the eight different DNAs have been invariably detected in field samples infected with the various geographical FBNYV isolates, experimental infection with different combinations of fewer than eight DNAs also led to typical FBNYV symptoms. Even only five genome components, DNA-R, DNA-S, DNA-M, DNA-U1 and DNA-U2, were sufficient for inducing disease symptoms in V. faba upon agroinoculation. Symptomatic plants agroinoculated or bombarded with eight DNAs contained typical FBNYV virions; however, the virus was not transmitted by Aphis craccivora or Acyrthosiphon pisum, two efficient aphid vectors of FBNYV.

Animals↗
PubMed1999

Faba bean necrotic yellows virus (genus Nanovirus) requires a helper factor for its aphid transmission.

Purified faba bean necrotic yellows virus (FBNYV; genus Nanovirus) alone is not transmissible by its aphid vector, Acyrthosiphon pisum, regardless of whether it is acquired from artificial diets or directly microinjected into the aphid's hemocoel. The purified virus contains all of the genetic information required for its infection cycle as it readily replicated in cowpea protoplasts and systemically infected Vicia faba seedlings that were biolistically inoculated using gold particles coated with intact virions or viral DNA. The bombarded plants not only developed the typical disease syndrome, thus indicating that FBNYV is the sole causal agent of the disease, but also served as a source from which the virus was readily acquired and transmitted by A. pisum. The defect of the purified virus in aphid transmissibility suggests that FBNYV requires a helper factor (HF) for its vector transmission that is either nonfunctional or absent in purified virus suspensions. The requirement for an HF was confirmed in complementation experiments using two distinct isolates of the virus. These experiments revealed that aphids transmitted the purified virus isolate from artificial diets only when they had fed previously on plants infected with the other FBNYV isolate. Also, microinjected FBNYV, which persisted to the same extent in A. pisum as naturally acquired virus, was transmissible when aphids had acquired the HF from infected plants. This suggests that one of the functions of the HF in the transmission process is to facilitate virus transport across the hemocoel-salivary gland interface.

Amino Acid Sequence↗
PubMed2001

Banana bunchy top nanovirus DNA-1 encodes the 'master' replication initiation protein.

Banana bunchy top nanovirus has a multicomponent, circular single-stranded DNA genome comprising at least six integral components, BBTV DNA-1 to -6, which have been consistently associated with bunchy top disease worldwide. At least three other components, BBTV S1, S2 and Y, which have been isolated from Taiwanese BBTV isolates, do not appear to be integral components. We show here that both BBTV DNA-1 and S1, which encode replication initiation (Rep) proteins, were capable of self-replication when bombarded into banana embryogenic cell suspensions. However, only BBTV DNA-1 was capable of directing the replication of two other BBTV genomic components, namely BBTV DNA-3 which encodes the coat protein, and DNA-5 which encodes a retinoblastoma binding-like protein. These results indicate that (i) BBTV DNA-1 is the minimal replicative unit of BBTV and encodes the 'master' viral Rep and (ii) BBTV S1 is possibly a satellite DNA which is unable to replicate integral BBTV components.

Biolistics↗
PubMed2000

Activities associated with the putative replication initiation protein of coconut foliar decay virus, a tentative member of the genus Nanovirus.

The putative replication initiation protein (Rep) of Coconut foliar decay virus (CFDV) was expressed as a 6x His recombinant protein in E. coli and in recombinant baculovirus. Purified 6x His-Rep protein was demonstrated to possess sequence non-specific RNA- and ssDNA-binding activities as well as magnesium-dependent ATPase/GTPase activity. The yeast two-hybrid system revealed that CFDV Rep could interact with itself. Subcellular distribution of the CFDV Rep was studied by fractionation of insect cells infected with recombinant baculovirus expressing the 6x His-Rep protein and by laser scanning confocal microscopy of Nicotiana benthamiana epidermal cells bombarded with a construct encoding CFDV Rep fused to GFP. It was shown that CFDV Rep associated predominantly with nuclei and membranes of infected/transfected cells. These activities of CFDV-encoded Rep are very similar to those reported for Reps of geminiviruses.

Adenosine Triphosphatases↗
PubMed2000

Clink, a nanovirus-encoded protein, binds both pRB and SKP1.

Clink, a 20-kDa protein of faba bean necrotic yellows virus, a single-stranded DNA plant virus, interacts with pRB family members and a SKP1 homologue from Medicago sativa. An LxCxE motif and an F-box of Clink mediate the interactions with the respective proteins. The capacity of Clink to bind pRB correlates with its ability to stimulate viral replication. Interaction of a single protein with the cell cycle regulator pRB and SKP1, a constituent of the ubiquitin-protein turnover pathway, appears to be a novel feature. Hence, Clink may represent a new class of viral cell cycle modulators.

Amino Acid Motifs↗
PubMed1999

Evidence that a plant virus switched hosts to infect a vertebrate and then recombined with a vertebrate-infecting virus.

There are several similarities between the small, circular, single-stranded-DNA genomes of circoviruses that infect vertebrates and the nanoviruses that infect plants. We analyzed circovirus and nanovirus replication initiator protein (Rep) sequences and confirmed that an N-terminal region in circovirus Reps is similar to an equivalent region in nanovirus Reps. However, we found that the remaining C-terminal region is related to an RNA-binding protein (protein 2C), encoded by picorna-like viruses, and we concluded that the sequence encoding this region of Rep was acquired from one of these single-stranded RNA viruses, probably a calicivirus, by recombination. This is clear evidence that a DNA virus has incorporated a gene from an RNA virus, and the fact that none of these viruses code for a reverse transcriptase suggests that another agent with this capacity was involved. Circoviruses were thought to be a sister-group of nanoviruses, but our phylogenetic analyses, which take account of the recombination, indicate that circoviruses evolved from a nanovirus. A nanovirus DNA was transferred from a plant to a vertebrate. This transferred DNA included the viral origin of replication; the sequence conservation clearly indicates that it maintained the ability to replicate. In view of these properties, we conclude that the transferred DNA was a kind of virus and the transfer was a host-switch. We speculate that this host-switch occurred when a vertebrate was exposed to sap from an infected plant. All characterized caliciviruses infect vertebrates, suggesting that the host-switch happened first and that the recombination took place in a vertebrate.

Amino Acid Sequence↗
PubMed2006

Reassortment and concerted evolution in banana bunchy top virus genomes.

The nanovirus Banana bunchy top virus (BBTV) has six standard components in its genome and occasionally contains components encoding additional Rep (replication initiation protein) genes. Phylogenetic network analysis of coding sequences of DNA 1 and 3 confirmed the two major groups of BBTV, a Pacific and an Asian group, but show evidence of web-like phylogenies for some genes. Phylogenetic analysis of 102 major common regions (CR-Ms) from all six components showed a possible concerted evolution within the Pacific group, which is likely due to recombination in this region. The CR-M of additional Rep genes is close to that of DNA 1 and 2. Comparison of tree topologies constructed with DNA 1 and DNA 3 coding sequences of 14 BBTV isolates showed distinct phylogenetic histories based on Kishino-Hasegawa and Shimodaira-Hasegawa tests. The results of principal component analysis of amino acid and codon usages indicate that DNA 1 and 3 have a codon bias different from that of all other genes of nanoviruses, including all currently known additional Rep genes of BBTV, which suggests a possible ancient genome reassortment event between distinctive nanoviruses.

Asia↗
PubMed2005

Plant viral intergenic DNA sequence repeats with transcription enhancing activity.

BACKGROUND: The geminivirus and nanovirus families of DNA plant viruses have proved to be a fertile source of viral genomic sequences, clearly demonstrated by the large number of sequence entries within public DNA sequence databases. Due to considerable conservation in genome organization, these viruses contain easily identifiable intergenic regions that have been found to contain multiple DNA sequence elements important to viral replication and gene regulation. As a first step in a broad screen of geminivirus and nanovirus intergenic sequences for DNA segments important in controlling viral gene expression, we have 'mined' a large set of viral intergenic regions for transcriptional enhancers. Viral sequences that are found to act as enhancers of transcription in plants are likely to contribute to viral gene activity during infection. RESULTS: DNA sequences from the intergenic regions of 29 geminiviruses or nanoviruses were scanned for repeated sequence elements to be tested for transcription enhancing activity. 105 elements were identified and placed immediately upstream from a minimal plant-functional promoter fused to an intron-containing luciferase reporter gene. Transient luciferase activity was measured within Agrobacteria-infused Nicotiana tobacum leaf tissue. Of the 105 elements tested, 14 were found to reproducibly elevate reporter gene activity (>25% increase over that from the minimal promoter-reporter construct, p < 0.05), while 91 elements failed to increase luciferase activity. A previously described "conserved late element" (CLE) was identified within tested repeats from 5 different viral species was found to have intrinsic enhancer activity in the absence of viral gene products. The remaining 9 active elements have not been previously demonstrated to act as functional promoter components. CONCLUSION: Biological significance for the active DNA elements identified is supported by repeated isolation of a previously defined viral element (CLE), and the finding that two of three viral enhancer elements examined were markedly enriched within both geminivirus sequences and within Arabidopsis promoter regions. These data provide a useful starting point for virologists interested in undertaking more detailed analysis of geminiviral promoter function.

Arabidopsis↗
PubMed2025

Construction and Segmental Reconstitution of Full-Length Infectious Clones of Milk Vetch Dwarf Virus.

The construction of infectious clones (ICs) is essential for studying viral replication, pathogenesis, and host interactions. Milk vetch dwarf virus (MDV), a nanovirus with a multipartite, single-stranded DNA genome, presents unique challenges for IC development due to its segmented genome organization. To enable functional analysis of its genome, we constructed full-length tandem-dimer-based ICs for all eight MDV genomic segments. Each segment was cloned into a binary vector and co-delivered into Nicotiana benthamiana, Nicotiana tabacum, Vicia faba, and Vigna unguiculata plants via Agrobacterium-mediated inoculation. Systemic infection was successfully reconstituted in all host plants, with PCR-based detection confirming the presence of all viral segments in the infected leaves of nearly all tested plants. Segmental accumulation in infected plants was quantified using qPCR, revealing non-equimolar distribution across hosts. This study establishes the first complete IC system for MDV, enabling reproducible infection, replication analysis, and quantitative segment profiling. It provides a foundational tool for future molecular investigations into MDV replication, host interactions, and viral movement, advancing our understanding of nanovirus biology and transmission dynamics.

Nicotiana↗