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Featured Application: The present work can contribute to understanding the origin of the Banana bunchy top virus isolates that occur in Mozambique, allowing phytosanitary organizations to trace the trajectory of the spread of the virus on the African continent and support control measures to avoid further damage. Banana bunchy top virus (BBTV) was recently detected in Mozambique and appears to be limited to the provinces of Gaza, Maputo and Zambezia, but it has great potential to spread to other provinces. Despite its importance, nothing is known about the BBTV isolates that occur in Mozambique. In this study, the sequences of the S and R genes of forty isolates chosen as representatives of samples collected previously from eleven farms of the four administrative posts of the district of Chóckwè, province of Gaza, were sequenced and analyzed. The S-DNA nucleotide sequences of the analyzed isolates were highly conserved, with identity ranging from 97% to 100%. The same was observed for the R-DNA sequences, with most identities ranging between 98% and 100% among the isolates from Chókwè and above 90% when compared to the isolates from GenBank. The phylogenetic analysis showed that the Mozambican BBTV isolates belong to the Pacific–Indian Oceans (PIO) group, showing greater proximity to the isolate JQ820453 from Malawi than to the isolates from sub-Saharan countries, which were grouped in a distinct subclade. This is the first study conducted to determine the molecular characteristics of BBTV isolates present in Mozambique. [ABSTRACT FROM AUTHOR]

During a project investigating pea viruses in the United Kingdom and developing a workflow for high-throughput sequencing in crop surveillance, pea necrotic yellow dwarf virus (PNYDV) was identified at one site, along with pea enation mosaic virus-1, pea enation mosaic virus-2, pea enation mosaic virus satellite RNA, pea seedborne mosaic virus, and turnip yellows virus. Following an initial finding of small PNYDV contigs by an RNA sequencing protocol on MiSeq (Illumina), confirmation and prevalence testing by PCR and Sanger sequencing determined the average PNYDV prevalence to be 3%. This is the first report of PNYDV, and a nanovirus, in the United Kingdom. Initial characterization of the octopartite genome by PCR revealed that component DNA N had a truncated sequence that differed from those previously reported. This led to confirmation testing using rolling circle amplification (RCA) into MiSeq and then MinION (Oxford Nanopore). Sequences were obtained by both RCA-MiSeq and RCA-MinION, with MinION producing more complete genomes than RCA-MiSeq. Data obtained from sequencing were used to provide an initial estimation of the genomic formula of PNYDV. Previous work has looked into comparing each method; however, this study shows how these methods can be used together. The truncated sequence for DNA N was also found by RCA-MiSeq and RCA-MinION and confirmed by specific primers, but further work is required to understand the impact of this truncation. [Figure: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Nanoviruses have multipartite, circular, single‐stranded DNA genomes and cause huge production losses in legumes and other crops. No viral suppressor of RNA silencing (VSR) has yet been reported from a member of the genus Nanovirus. Here, we demonstrate that the nanovirus U2 protein is a VSR. The U2 protein of milk vetch dwarf virus (MDV) suppressed the silencing of the green fluorescent protein (GFP) gene induced by single‐stranded and double‐stranded RNA, and the systemic spread of the GFP silencing signal. An electrophoretic mobility shift assay showed that the U2 protein was able to bind double‐stranded 21‐nucleotide small interfering RNA (siRNA). The cysteine residues at positions 43, 79 and 82 in the MDV U2 protein are critical to its nuclear localization, self‐interaction and siRNA‐binding ability, and were essential for its VSR activity. In addition, expression of the U2 protein via a potato virus X vector induced more severe necrosis symptoms in Nicotiana benthamiana leaves. The U2 proteins of other nanoviruses also acted as VSRs, and the three conserved cysteine residues were indispensable for their VSR activity. [ABSTRACT FROM AUTHOR]

Black locust (Robinia pseudoacacia L., Fabaceae) is a shade tree and commonly used in urban green spaces in Iran. In the current study, 13 symptomatic black locust samples showing withering and decline were collected within the campus of Shahid Bahonar University of Kerman (southeastern Iran) and sophora yellow stunt virus (SYSV, genus Nanovirus, family Nanoviridae) was detected in two samples using nanovirus degenerate primers by PCR assay and sequencing of amplicons. Subsequently, eight genome components of the Rob4 isolate were amplified using specific primer pairs and sequenced. Sequence analysis showed that the Rob4 isolate shared 93.3–99.8% nucleotide identity with the previously sequenced genome of isolate Ta1 from a plant of Sophora alopecuroides also growing at the university campus and 68.9–99.8% nucleotide identity with the other sequences of SYSV available in GenBank. To demonstrate the pathogenesis of SYSV in black locust seedlings, previously constructed clones of the SYSV genome components were used for agroinoculation resulting in the appearance of severe symptoms followed by wilting and death of seedlings. Based on the results of this study, black locust tree is identified as a permanent reservoir host of SYSV in Iran. To the best of our knowledge, this is the first report of the infection of a nanovirus with a symptomatic perennial tree having woody trunk. [ABSTRACT FROM AUTHOR]

Banana bunchy top virus (BBTV) was recently detected in Mozambique and appears to be limited to the provinces of Gaza, Maputo and Zambezia, but it has great potential to spread to other provinces. Despite its importance, nothing is known about the BBTV isolates that occur in Mozambique. In this study, the sequences of the S and R genes of forty isolates chosen as representatives of samples collected previously from eleven farms of the four administrative posts of the district of Chóckwè, province of Gaza, were sequenced and analyzed. The S-DNA nucleotide sequences of the analyzed isolates were highly conserved, with identity ranging from 97% to 100%. The same was observed for the R-DNA sequences, with most identities ranging between 98% and 100% among the isolates from Chókwè and above 90% when compared to the isolates from GenBank. The phylogenetic analysis showed that the Mozambican BBTV isolates belong to the Pacific–Indian Oceans (PIO) group, showing greater proximity to the isolate JQ820453 from Malawi than to the isolates from sub-Saharan countries, which were grouped in a distinct subclade. This is the first study conducted to determine the molecular characteristics of BBTV isolates present in Mozambique.

Banana bunchy top virus is reported for the first time in Laos. Infected plants showed typical disease symptoms and the two complete genome sequences reported place the isolates in the Southeast Asian subgroup. [ABSTRACT FROM AUTHOR]

In this study, NEBcutter is used in generating the restriction enzymes map of the circular sequence of BBTV-DNA components (DNA-R, DNA-U3, DNA-S, DNA-M, DNA-M and DNA-N) appearing with each cleavage code and enzyme name code. Results showed that the closest enzymes at the 5' end of the restriction sites of HphI, ApoI, BtsIMutI, Fnu4HI, Hpy99I and BccI were detected for the six BBTV-DNA components, receptively. While, the restriction sites of Cac8I, AluI, Hpy166II, DpnII, AccI and AseI were detected as the closest enzymes at 3' end for the same components, respectively. These BBTV-DNA components were encoding the genes of replication-associated protein (BBJ34149.1, 278 aa), U3 protein (BBJ34150.1, 88 aa), capsid protein (BBJ34151.1, 175 aa), movement protein (BBJ34152.1, 102 aa), cell-cycle link protein (BBJ34153.1, 156 aa) and nuclear shuttle protein (BBJ34154.1, 129 aa), respectively. Similarity ranged from 95 to 100% found when sequences producing significant alignments were done between the ORFs of BBTV-DNA components and the most similar BBTV overseas strains. The number and type of domains of the ORFs of the six BBTV components and their families were determined. Two domains were found for DNA-R (viral rep and RNA_helicase domains). NA-U3 has a hypothetical protein belonging to un-characterized protein U3 domain, one domain called nanovirus_coat the protein family membership is Nanovirus coat protein recorded for DNA-S, DNA-M has one domain Babovirus_MP, DNA-C has a domain belonging to cell cycle protein and DNA-N has a domain belonging to nuclear shuttle protein domain. [ABSTRACT FROM AUTHOR]

Banana is the major staple food crop for approximately 400 million people. Bunchy top disease of banana is one of the most devastating diseases caused by banana bunchy top virus (BBTV), which results in stunting of plants, bunchy appearance of leaves and a significant loss of yield. While many isolates of BBTV from various regions of India have been characterized by different groups, no structural study exists for this important virus. To bridge this gap, the pET28a clone of the coat protein (CP) gene from BBTV isolate of Hill banana grown in lower Pulney Hills (Virupakshi) of Tamilnadu was expressed in BL21 (DE3) pLysS. Purification of the CP was achieved by Ni–NTA affinity chromatography. In vitro capsid assembly studied using sucrose density gradient centrifugation suggested that the CP did not assemble as a virus-like particle (VLP), but remained as smaller oligomers. Studies using dynamic light scattering (DLS) indicate that the purified protein is poly-dispersed, represented majorly as pentamers. Homology modeling studies provided useful insights into the probable fold of the CP suggesting that it is a β-sandwich, similar to that seen in the majority of plant viruses. In silico capsid reconstruction aided the understanding of the quaternary organization of subunits in the capsid and their molecular interactions. The location of the aphid-binding EAG motif was identified on the surface loops close to the pentameric axis indicating its role in vector-mediated transmission. Comparison with the CP and capsid structure of geminiviruses provided useful insights into the mode of nucleic acid binding and the role of genome during capsid assembly. [ABSTRACT FROM AUTHOR]

Sophora alopecuroides is an important shrub widely distributed in arid and semi-arid regions of Asia. Recently, S. alopecuroides plants with symptoms of severe stunting, yellowing and small sized leaves were observed in Wuhai, Inner Mongolia, of China. In this work, the infection of Sophora yellow stunt virus (SYSV), a virus belonging to the genus Nanovirus, was confirmed by next-generation sequencing of small RNAs. The complete genome of the SYSV CH isolate, including eight circular single-stranded DNA components, was amplified by PCR and sequenced. SYSV-CH shared 87.0% identity in overall nucleotide sequence with SYSV-IR:Har:H13:Soph:17 isolate. Both of phylogenetic analysis based on individual DNA components and recombination analysis based on concatenated components supported the hypothesis that SYSV-CH might be a reassortment isolate whose DNA-R originated from faba bean necrotic yellows virus. In addition, an alphasatellite was identified and sequenced. To our knowledge, this is the first report of occurrence and complete genome sequence of SYSV from China. [ABSTRACT FROM AUTHOR]

Nanoviruses are plant viruses with a multipartite single-stranded DNA (ssDNA) genome. Alphasatellites are commonly associated with nanovirus infections, but their putative impact on their helper viruses is unknown. In this study, we investigated the role of subterranean clover stunt alphasatellite 1 (here named SCSA 1) on various important traits of Faba bean necrotic yellows virus (FBNYV) in its host plant Vicia faba and aphid vector Acyrthosiphon pisum, including disease symptoms, viral accumulation, and viral transmission. The results indicate that SCSA 1 does not affect the severity of symptoms nor overall FBNYV accumulation in V. faba, but it does change the relative amounts of its different genomic segments. Moreover, the association of SCSA 1 with FBNYV increases the rate of plant-to-plant transmission by a process seemingly unrelated to the simple increase of viral accumulation in the vector. These results represent the first study on the impact of an alphasatellite on the biology of its helper nanovirus. They suggest that SCSA 1 may benefit FBNYV, but the genericity of this conclusion is discussed and questioned. [ABSTRACT FROM AUTHOR]

Multipartite viruses exhibit a fragmented genome composed of several nucleic acid segments individually packaged in distinct viral particles. The genome of all species of the genus Nanovirus holds eight segments, which accumulate at a very specific and reproducible relative frequency in the host plant tissues. In a given host species, the steady state pattern of the segments' relative frequencies is designated the genome formula and is thought to have an adaptive function through the modulation of gene expression. Nanoviruses are aphid-transmitted circulative non-propagative viruses, meaning that the virus particles are internalized into the midgut cells, transferred to the hemolymph, and then to the saliva, with no replication during this transit. Unexpectedly, a previous study on the faba bean necrotic stunt virus revealed that the genome formula changes after ingestion by aphids. We investigate here the possible mechanism inducing this change by first comparing the relative segment frequencies in different compartments of the aphid. We show that changes occur both in the midgut lumen and in the secreted saliva but not in the gut, salivary gland, or hemolymph. We further establish that the viral particles differentially resist physicochemical variations, in particular pH, ionic strength, and/or type of salt, depending on the encapsidated segment. We thus propose that the replication-independent genome formula changes within aphids are not adaptive, contrary to changes occurring in plants, and most likely reflect a fortuitous differential degradation of virus particles containing distinct segments when passing into extra-cellular media such as gastric fluid or saliva., Importance: The genome of multipartite viruses is composed of several segments individually packaged into distinct viral particles. Each segment accumulates at a specific frequency that depends on the host plant species and regulates gene expression. Intriguingly, the relative frequencies of the genome segments also change when the octopartite faba bean necrotic stunt virus (FBNSV) is ingested by aphid vectors, despite the present view that this virus travels through the aphid gut and salivary glands without replicating. By monitoring the genomic composition of FBNSV populations during the transit in aphids, we demonstrate here that the changes take place extracellularly in the gut lumen and in the saliva. We further show that physicochemical factors induce differential degradation of viral particles depending on the encapsidated segment. We propose that the replication-independent changes within the insect vector are not adaptive and result from the differential stability of virus particles containing distinct segments according to environmental parameters., Competing Interests: The authors declare no conflict of interest.

Faba bean necrotic yellows virus (FBNYV) (Nanovirus, Nanoviridae) is a common nanovirus of leguminous plant in Asia, Africa and Europe continents. In this research, natural hosts of FBNYV in three eastern provinces of Iran have been studied and full-length genome components of a Rabor isolate (Kerman province) has been sequenced. To identify FBNYV natural hosts, leguminous plants and leaf vegetables were sampled in Kerman, Razavi Khorasan and Northern Khorasan, and the FBNYV infection of the samples was tested by PCR and/or nucleotide sequence of DNA-S component. Results indicated that lentil, faba bean, broad bean, chickpea, alfalfa, fenugreek, parsley and dill are infected with FBNYV and DNA-S of seven isolates from seven plant species share 89.6-99.7% nucleotide sequence identities. Among infected hosts, full-length genome components of a chickpea isolate of FBNYV from Rabor (Kerman province) was determined and compared with the related components of the GenBank isolates. Accordingly, all genome components of the Rabor isolate shared 88.57-99.81% nucleotide sequence identities with the corresponding sequence of other Iranian and GenBank isolates. To conclude, FBNYV has a broad host range in leguminous plants and even can infect non-leguminous leaf vegetables. It is the first report of the FBNYV infection of fenugreek, parsley and dill in the world. [ABSTRACT FROM AUTHOR]

Abstract Background Tobacco production in China has been affected by plant viruses with Milk vetch dwarf virus (MDV) as a recent invader posing serious concern. According to most of the studies, MDV mainly infects hosts from Fabaceae family but in our previous study we reported its infection in tobacco plant (Nicotiana tabacum L.) in Shandong province. Findings In current study (2016–2017), tobacco plants (Nicotiana tabacum) with severe stunting, yellowing and axillary bunch of new leaves were observed in Zhengning, Gansu province. Isolate GSZN yielded into eight genomic circular single-stranded DNA components while no alphasatellite DNA was obtained. High percent identity of this isolate was recorded in overall nucleotide and amino acid assembly with reported MDV isolates worldwide. Phylogenetic analysis fetched into a separate sub-clade comprising of new isolate along with other tobacco infecting isolates of MDV. While recombination was predicted in DNA-C encoding Clink protein and DNA-U1, which may attribute towards the potential host-shifting phenomenon and ability of this virus to expand its host range. Conclusion To our knowledge this is the first full genome annotation of a Nanovirus, infecting tobacco in natural field conditions, also this is the first extended analysis on host-shifting behavior of MDV.

Of the approximately 1,200 plant virus species that have been described to date, nearly one-third are single-stranded DNA (ssDNA) viruses, and all are transmitted by insect vectors. However, most studies of vector transmission of plant viruses have focused on RNA viruses. All known plant ssDNA viruses belong to two economically important families, Geminiviridae and Nanoviridae, and in recent years, there have been increased efforts to understand whether they have evolved similar relationships with their respective insect vectors. This review describes the current understanding of ssDNA virus–vector interactions, including how these viruses cross insect vector cellular barriers, the responses of vectors to virus circulation, the possible existence of viral replication within insect vectors, and the three-way virus–vector–plant interactions. Despite recent breakthroughs in our understanding of these viruses, many aspects of plant ssDNA virus transmission remain elusive. More effort is needed to identify insect proteins that mediate the transmission of plant ssDNA viruses and to understand the complex virus–insect–plant three-way interactions in the field during natural infection. [ABSTRACT FROM AUTHOR]

Milk vetch dwarf virus (MDV) is an important member of the genus Nanovirus and is transmitted by the aphid Aphis craccivora. MDV has multiple single‐stranded DNA genome components, each approximately 1 kb, and two or three alpha‐satellite molecules. It mainly infects plants of the legume family Fabaceae. Recently, papaya (Carica papaya) collected in Yesan, South Korea, displaying symptoms of leaf yellowing and dwarfism, was identified as a new host for MDV. To examine the geographical distribution of MDV, papaya samples with symptoms were harvested in South Korea, Vietnam, and Taiwan in August 2018, along with tomato and pepper samples grown in adjacent fields in Vietnam. The results revealed the presence of MDV not only in papaya but also in pepper and tomato. This MDV infection in members of the Solanaceae family was confirmed by Southern blot hybridization performed using a PCR product of segment S as a probe. Based on sequence analysis of three MDV components (M, S, and C3), we verified the presence of three different isolates of MDV in these three countries and homology between sequences of isolates from papaya and from members of the Solanaceae from Vietnam. Taken together, our results clearly demonstrate MDV infection in Vietnam and Taiwan for the first time and confirm that MDV can infect economically important pepper and tomato. [ABSTRACT FROM AUTHOR]

Faba bean necrotic yellows virus (FBNYV) causes severe yield losses and crop failure in legumes in the north African, south Asian and European countries. Following nucleotide sequencing of DNA-M segment of 17 host and geographical FBNYV isolates in Iran, different molecular analysis were performed based on all available DNA-M sequences of FBNYV. Based on constructed phylogenetic tree using nucleotide sequence of DNA-M component, FBNYV isolates were grouped into three clades, including isolates from Iran and Azerbaijan as a distinct clade. Genetic distance studies of FBNYV host subpopulations revealed some evidences of host adaptation in FBNYV natural selection. High gene flow was found among Iran – Azerbaijan and Spain – Africa subpopulations, indicating the relationship of their origins. Maximum genetic diversity of DNA-M was estimated in the central subpopulation of Iran. The dN/dS (Ѡ) value less than 1 represented the negative selection pressure on the movement protein of the virus. Seven out of nine recombination events were detected in DNA-M of Iranian FBNYV isolates. This is the first report of the FBNYV infection on pea from Iran. In the current study, the complete DNA-M nucleotide sequences of French bean and pea isolates of FBNYV were determined for the first time in the world. [ABSTRACT FROM AUTHOR]

Sophora yellow stunt-associated virus (SYSaV) (Nanovirus, Nanoviridae) is a new nanovirus that recently identified in Iran with wide distribution. In the present study, the SYSaV infection of chickpea (Cicer arietinum L.), lentil (Lens culinaris Medikus), liquorice (Glycyrrhiza glabra L.), esfand (Peganum harmala L.) and milk vetch (Astragalus sp.) showing typical nanovirus symptoms including dwarfing and yellowing was tested by PCR and full-length sequencing of selected genome components. Results indicated that these samples are infected with SYSaV. In transmission experiments, the capability of cowpea aphid (Aphis craccivora ) and pea aphid (Acyrthosiphon pisum) to transmit SYSaV to healthy plants was evaluated under greenhouse conditions. While Aphis craccivora transmitted the virus from infected to healthy sophora plants, Acyrthosiphon pisum collected on naturally infected sophora plants transmitted the virus to sophora, chickpea and cowpea seedlings. Based on the results of this study, beside the main host (sophora), SYSaV is able to infect two other medicinal plants. In addition, the host range of the virus is not limited to the wild species and at least two legume crops are infected with SYSaV. [ABSTRACT FROM AUTHOR]

Single-stranded DNA (ssDNA) plant viruses belong to the families Geminiviridae and Nanoviridae. They are transmitted by Hemipteran insects in a circulative, mostly non-propagative, manner. While geminiviruses are transmitted by leafhoppers, treehoppers, whiteflies and aphids, nanoviruses are transmitted exclusively by aphids. Circulative transmission involves complex virus−vector interactions in which epithelial cells have to be crossed and defense mechanisms counteracted. Vector taxa are considered a relevant taxonomic criterion for virus classification, indicating that viruses can evolve specific interactions with their vectors. Thus, we predicted that, although nanoviruses and geminiviruses represent related viral families, they have evolved distinct interactions with their vector. This prediction is also supported by the non-structural Nuclear Shuttle Protein (NSP) that is involved in vector transmission in nanoviruses but has no similar function in geminiviruses. Thanks to the recent discovery of aphid-transmitted geminiviruses, this prediction could be tested for the geminivirus alfalfa leaf curl virus (ALCV) and the nanovirus faba bean necrotic stunt virus (FBNSV) in their common vector, Aphis craccivora. Estimations of viral load in midgut and head of aphids, precise localization of viral DNA in cells of insect vectors and host plants, and virus transmission tests revealed that the pathway of the two viruses across the body of their common vector differs both quantitatively and qualitatively.

The experience with a diagnostic technology based on rolling circle amplification (RCA), restriction fragment length polymorphism (RFLP) analyses, and direct or deep sequencing (Circomics) over the past 15 years is surveyed for the plant infecting geminiviruses, nanoviruses and associated satellite DNAs, which have had increasing impact on agricultural and horticultural losses due to global transportation and recombination-aided diversification. Current state methods for quarantine measures are described to identify individual DNA components with great accuracy and to recognize the crucial role of the molecular viral population structure as an important factor for sustainable plant protection. [ABSTRACT FROM AUTHOR]

Im Jahr 2016 kam es deutschlandweit zu einem Auftreten von Viruserkrankungen an Leguminosen mit teilweise erheb­lichen Schäden. Im gesamten Bundesgebiet wurde das Nanovirus Pea necrotic yellow dwarf virus (PNYDV) nachgewiesen, erstmals auch an Ackerbohnen, Linsen und Wicken. Bislang war die Verbreitung des Virus auf Gemüseerbsen in wenigen Befallsgebieten beschränkt. Da PNYDV und andere Leguminosen befallende Pflanzenviren hauptsächlich durch Blattläuse übertragen werden, ist mit milderen Wintern in Deutschland infolge des Klimawandels und der damit einhergehenden längeren Flugperiode und anholozyklischen Überwinterung von Blattläusen zukünftig mit einem vermehrten Auftreten von Viren an Leguminosen zu rechnen.

Subterranean clover stunt virus (SCSV) is a type species of the genus Nanovirus in the family Nanoviridae. It was the first single-stranded DNA plant virus with a multipartite genome, of which genomic DNA sequences had been determined. All nanoviruses have eight genome components except SCSV, for which homologs of two genome components present in all other nanovirus genomes, DNA-U2 and DNA-U4, were lacking. We analysed archived and more recent samples from SCSV-infected legume plants to verify its genome composition and found the missing genome components. These results indicated that SCSV also has eight genome components and is a typical member of the genus Nanovirus.

Pea necrotic yellow dwarf virus (PNYDV) is a multipartite, circular, single-stranded DNA plant virus. PNYDV encodes eight proteins and the function of three of which remains unknown-U1, U2, and U4. PNYDV proteins cellular localization was analyzed by GFP tagging and bimolecular fluorescence complementation (BiFC) studies. The interactions of all eight PNYDV proteins were tested pairwise in planta (36 combinations in total). Seven interactions were identified and two (M-Rep with CP and MP with U4) were characterized further. MP and U4 complexes appeared as vesicle-like spots and were localized at the nuclear envelope and cell periphery. These vesicle-like spots were associated with the endoplasmatic reticulum. In addition, a nuclear localization signal (NLS) was mapped for U1, and a mutated U1 with NLS disrupted localized at plasmodesmata and therefore might also have a role in movement. Taken together, this study provides evidence for previously undescribed nanovirus protein-protein interactions and their cellular localization with novel findings not only for those proteins with unknown function, but also for characterized proteins such as the CP. [ABSTRACT FROM AUTHOR]

Viruses in the genus Nanovirus of the family Nanoviridae generally have eight individually encapsidated circular genome components and have been predominantly found infecting Fabaceae plants in Europe, Australia, Africa and Asia. For over a decade Sophora alopecuroides L. (Fabaceae) plants have been observed across Iran displaying dwarfing, yellowing, stunted leaves and yellow vein banding. Using a high-throughput sequencing approach, sequences were identified within one such plant that had similarities to nanovirus genome components. From this plant, the nanovirus-like molecules DNA-R ( n = 4), DNA-C ( n = 2), DNA-S ( n = 1), DNA-M ( n = 1), DNA-N ( n = 1), DNA-U1 ( n = 1), DNA-U2 ( n = 1) and DNA-U4 ( n = 1) were amplified, cloned and sequenced. Other than for the DNA-R, these components share less than 71% identity with those of other known nanoviruses. The four DNA-R molecules were highly diverse, sharing only 65–71% identity with each other and 64–86% identity with those of other nanoviruses. In the S. alopecuroides plant 14 molecules sharing 57.7–84.6% identity with previously determined sequences of nanovirus-associated alphasatellites were also identified. Given the research activity in the nanovirus field during the last five years coupled with high-throughput sequence technologies, many more diverse nanoviruses and nanovirus-associated satellites are likely to be identified. [ABSTRACT FROM AUTHOR]

In 2016, a country-wide virus outbreak was observed on legumes in Germany. Severe yield losses were reported in some cases. For the very first time, Pea necrotic yellow dwarf virus (PNYDV), a nanovirus, was not only found nationwide on peas in Germany but also infected faba beans, lentils and vetch. PNYDV was so far only found in few geographic regions of Germany. PNYDV as well as other legume-infecting viruses are mainly aphid-borne. It is expected that climate change will lead to milder winters in Germany therefore aphid flight periods will be extended. Furthermore, more aphids can overwinter as adults thus potentially enhancing virus incidences on legumes. [ABSTRACT FROM AUTHOR]

Stress granules (SGs) are structures within cells that regulate gene expression during stress response, e.g. viral infection. In mammalian cells assembly of SGs is dependent on the Ras-GAP SH3-domain–binding protein (G3BP). The C-terminal domain of the viral nonstructural protein 3 (nsP3) of Semliki Forest virus (SFV) forms a complex with mammalian G3BP and sequesters it into viral RNA replication complexes in a manner that inhibits the formation of SGs. The binding domain of nsP3 to HsG3BP was mapped to two tandem ‘FGDF’ repeat motifs close to the C-terminus of the viral proteins. It was speculated that plant viruses employ a similar strategy to inhibit SG function. This study identifies an Arabidopsis thaliana NTF2-RRM domain-containing protein as a G3BP-like protein (AtG3BP), which localizes to plant SGs. Moreover, the nuclear shuttle protein (NSP) of the begomovirus abutilon mosaic virus (AbMV), which harbors a ‘FVSF’-motif at its C-terminal end, interacts with the AtG3BP-like protein, as does the ‘FNGSF’-motif containing NSP of pea necrotic yellow dwarf virus (PNYDV), a member of the Nanoviridae family. We therefore propose that SG formation upon stress is conserved between mammalian and plant cells and that plant viruses may follow a similar strategy to inhibit plant SG function as it has been shown for their mammalian counterparts. [ABSTRACT FROM AUTHOR]

Although single stranded (ss) DNA viruses that infect humans and their domesticated animals do not generally cause major diseases, the arthropod borne ssDNA viruses of plants do, and as a result seriously constrain food production in most temperate regions of the world. Besides the well known plant and animal-infecting ssDNA viruses, it has recently become apparent through metagenomic surveys of ssDNA molecules that there also exist large numbers of other diverse ssDNA viruses within almost all terrestrial and aquatic environments. The host ranges of these viruses probably span the tree of life and they are likely to be important components of global ecosystems. Various lines of evidence suggest that a pivotal evolutionary process during the generation of this global ssDNA virus diversity has probably been genetic recombination. High rates of homologous recombination, non-homologous recombination and genome component reassortment are known to occur within and between various different ssDNA virus species and we look here at the various roles that these different types of recombination may play, both in the day-to-day biology, and in the longer term evolution, of these viruses. We specifically focus on the ecological, biochemical and selective factors underlying patterns of genetic exchange detectable amongst the ssDNA viruses and discuss how these should all be considered when assessing the adaptive value of recombination during ssDNA virus evolution.

The experience with a diagnostic technology based on rolling circle amplification (RCA), restriction fragment length polymorphism (RFLP) analyses, and direct or deep sequencing (Circomics) over the past 15 years is surveyed for the plant infecting geminiviruses, nanoviruses and associated satellite DNAs, which have had increasing impact on agricultural and horticultural losses due to global transportation and recombination-aided diversification. Current state methods for quarantine measures are described to identify individual DNA components with great accuracy and to recognize the crucial role of the molecular viral population structure as an important factor for sustainable plant protection.

Banana bunchy top virus (BBTV) is a multi-component single-stranded DNA virus. From 267 potentially infected Musa plants, 24 apparently 'defective' BBTV components have been identified. Interestingly, 23/24 of these defective molecules were apparently derived from DNA-R. All of the identified defective molecules had retained at least part of the CR-SL and CR-M but had insertions and/or deletions that in most cases resulted in open reading frame disruptions. Our detection of three monophyletic but diverse (and therefore likely circulating) defective DNA-R lineages suggests that, in many cases, defective DNA-R molecules might remain associated with BBTV genomes for prolonged periods. [ABSTRACT FROM AUTHOR]

Geminiviruses, single-stranded DNA plant viruses, encode a replication-initiator protein (Rep) that is indispensable for virus replication. A potential cyclin interaction motif (RXL) in the sequence of African cassava mosaic virus Rep may be an alternative link to cell cycle controls to the known interaction with plant homologs of retinoblastoma protein (pRBR). Mutation of this motif abrogated rereplication in fission yeast induced by expression of wildtype Rep suggesting that Rep interacts via its RXL motif with one or several yeast proteins. The RXL motif is essential for viral infection of Nicotiana benthamiana plants, since mutation of this motif in infectious clones prevented any symptomatic infection. The cell-cycle link (Clink) protein of a nanovirus (faba bean necrotic yellows virus) was investigated that activates the cell cycle by binding via its LXCXE motif to pRBR. Expression of wildtype Clink and a Clink mutant deficient in pRBR-binding did not trigger rereplication in fission yeast. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assessed reassortment and recombination among CBDV isolates from Northeast India. [•] Patterns of reassortment were biased to specific genome components. [•] Inter-component recombination events indicate a process of concerted evolution. [•] Rates of reassortment and inter-component recombination appear to be associated. [ABSTRACT FROM AUTHOR]

Although single stranded (ss) DNA viruses that infect humans and their domesticated animals do not generally cause major diseases, the arthropod borne ssDNA viruses of plants do, and as a result seriously constrain food production in most temperate regions of the world. Besides the well known plant and animal-infecting ssDNA viruses, it has recently become apparent through metagenomic surveys of ssDNA molecules that there also exist large numbers of other diverse ssDNA viruses within almost all terrestrial and aquatic environments. The host ranges of these viruses probably span the tree of life and they are likely to be important components of global ecosystems. Various lines of evidence suggest that a pivotal evolutionary process during the generation of this global ssDNA virus diversity has probably been genetic recombination. High rates of homologous recombination, non-homologous recombination and genome component reassortment are known to occur within and between various different ssDNA virus species and we look here at the various roles that these different types of recombination may play, both in the day-to-day biology, and in the longer term evolution, of these viruses. We specifically focus on the ecological, biochemical and selective factors underlying patterns of genetic exchange detectable amongst the ssDNA viruses and discuss how these should all be considered when assessing the adaptive value of recombination during ssDNA virus evolution. [ABSTRACT FROM AUTHOR]

Five genes encoded by Banana bunchy top virus (BBTV) originating from Pakistan were expressed in Nicotiana benthamiana using a Potato virus X (PVX) vector. Expression of the master replication-associated protein (mRep) and movement protein (MP) resulted in necrotic cell death of inoculated tissues, as well as leaf curling and necrosis along the veins in newly emerging leaves. The systemic necrosis induced by the expression of MP was discolored (dark) in comparison to that induced by mRep. Expression of the cell-cycle link protein (Clink), the coat protein (CP), and the nuclear shuttle protein from the PVX vector induced somewhat milder symptoms, consisting of mild leaf curling and mosaic, although expression of the CP caused a necrotic response in inoculated leaf. The accumulation of viral RNA was enhanced by MP, Clink, and CP. Of the five BBTV-encoded gene products two, the MP and Clink, stabilized GFP-specific mRNA and reduced GFP-specific small interfering RNA in N. benthamiana line 16c when expressed under the control of the 35S promoter and co-inoculated with a construct for the expression of GFP hairpin RNA construct. These results identified MP and Clink as suppressors of RNA silencing. Taken together the ability of MP to induce severe symptoms in plants and suppress RNA silencing implicates this product as a major pathogenicity determinant of BBTV. [ABSTRACT FROM AUTHOR]

Multicomponent ssDNA plant viruses were discovered during 1990s. They are associated with bunchy top, yellowing and dwarfing diseases of several economic plants under family Musaceae, Leguminosae and Zingiberaceae. In the current plant virus taxonomy, these viruses are classified under the family Nanoviridae containing two genera, Nanovirus and Babuvirus. The family Nanoviridae was created with five members in 2005 and by 2010, it has expanded with four additional members. The viruses are distributed in the tropical and subtropical regions of Asia, Australia, Europe and Africa. The viruses are not sap or seed transmissible and are naturally transmitted by aphid vector in a persistent manner. The genome is consisted of several circular ssDNAs of about 1 kb each. Up to 12 DNA components have been isolated from the diseased plant. The major viral proteins encoded by these components are replication initiator protein (Rep), coat protein, cell-cycle link protein, movement protein and a nuclear shuttle protein. Each ssDNA contains a single gene and a noncoding region with a stable stem and loop structure. Several Rep encoding components have been reported from each virus, only one of them designated as master Rep has ability to control replication of the other genomic components. Infectivity of the genomic DNAs was demonstrated only for two nanoviruses, Faba bean necrotic yellows virus and Faba bean necrotic stunt virus (FBNSV). A group of eight ssDNA components of FBNSV were necessary for producing disease and biologically active progeny viruses. So far, infectivity of genomic components of Babuvirus has not been demonstrated. [ABSTRACT FROM AUTHOR]