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Endogenous viral elements (EVEs) have been reported to exist widely in the genomes of eukaryotic organisms, and they are closely associated with the growth, development, genetics, adaptation, and evolution of their hosts. In this study, two methods—homologous sequence search and genome alignment—were used to explore the endogenous viral sequences in the genomes of Fragaria species. Results revealed abundant endogenous pararetroviruses (EPRVs) in the genomes of Fragaria species, including 786 sequences belonging to five known taxa such as Caulimovirus and other unclassified taxa. Differences were observed in the detected EPRVs between the two methods, with the homologous sequence search having a greater number of EPRVs. On the contrary, genome alignment identified various types and sources of virus-like sequences. Furthermore, through genome alignment, a 267-bp sequence with 95% similarity to the gene encoding the aphid-transmitted protein of Strawberry vein banding virus (Caulimovirus venafragariae) was discovered in the F. chiloensis genome, which was likely a recent insertion. In addition, the statistical analysis of the genome alignment results indicated a remarkably higher abundance of virus-like sequences in the genomes of polyploid strawberries compared with diploid ones. Moreover, the differences in virus-like sequences were observed between the genomes of Fragaria species and those of their close relatives. This study enriched the diversity of viruses that infect strawberries, and laid a theoretical foundation for further research on the origin of endogenous viruses in the strawberry genome, host–virus interactions, adaptation, evolution, and their functions. [ABSTRACT FROM AUTHOR]

The cacao swollen shoot disease (CSSD) caused by a complex of badnavirus species presents a major challenge for cacao production in West Africa, especially Ghana and Côte d'Ivoire. In this study, CSSD species detection efficiency, diversity, and geographic distribution patterns in cacao plantations in Ghana and Côte d'Ivoire were investigated through field surveillance, PCR detection assays, sequencing of positive amplicons, and phylogeographic clustering. Cumulatively, the detection efficiency of the tested CSSD primer sets that were targeting the movement protein domain of the virus ranged from 0.15% (CSSD-3 primer) to 66.91% (CSSD-1 primer) on all the symptomatic cacao leaf samples assessed. The identified CSSD species differed phylogenetically and overlapped in distribution, with the cacao swollen shoot Togo B virus (CSSTBV) (n = 588 sequences) being the most prevalent and widely distributed compared to the other CSSD species that were encountered in both countries. Geographically, the cacao swollen shoot CE virus (CSSCEV) species (n = 124 sequences) that was identified was largely restricted to the bordering regions of Ghana and Côte d'Ivoire. These results provide updated knowledge of the geographic distribution of the key CSSD species and their diagnostic efficiency and, thus, provide guidance in identifying locations for structured testing of cacao germplasm and optimal diagnostics for the predominant CSSD species in Ghana and Côte d'Ivoire. [ABSTRACT FROM AUTHOR]

Endogenous viral elements (EVEs) have been reported to exist widely in the genomes of eukaryotic organisms, and they are closely associated with the growth, development, genetics, adaptation, and evolution of their hosts. In this study, two methods—homologous sequence search and genome alignment—were used to explore the endogenous viral sequences in the genomes of Fragaria species. Results revealed abundant endogenous pararetroviruses (EPRVs) in the genomes of Fragaria species, including 786 sequences belonging to five known taxa such as Caulimovirus and other unclassified taxa. Differences were observed in the detected EPRVs between the two methods, with the homologous sequence search having a greater number of EPRVs. On the contrary, genome alignment identified various types and sources of virus-like sequences. Furthermore, through genome alignment, a 267-bp sequence with 95% similarity to the gene encoding the aphid-transmitted protein of Strawberry vein banding virus (Caulimovirus venafragariae) was discovered in the F. chiloensis genome, which was likely a recent insertion. In addition, the statistical analysis of the genome alignment results indicated a remarkably higher abundance of virus-like sequences in the genomes of polyploid strawberries compared with diploid ones. Moreover, the differences in virus-like sequences were observed between the genomes of Fragaria species and those of their close relatives. This study enriched the diversity of viruses that infect strawberries, and laid a theoretical foundation for further research on the origin of endogenous viruses in the strawberry genome, host–virus interactions, adaptation, evolution, and their functions.

The cacao swollen shoot disease (CSSD) caused by a complex of badnavirus species presents a major challenge for cacao production in West Africa, especially Ghana and Côte d’Ivoire. In this study, CSSD species detection efficiency, diversity, and geographic distribution patterns in cacao plantations in Ghana and Côte d’Ivoire were investigated through field surveillance, PCR detection assays, sequencing of positive amplicons, and phylogeographic clustering. Cumulatively, the detection efficiency of the tested CSSD primer sets that were targeting the movement protein domain of the virus ranged from 0.15% (CSSD-3 primer) to 66.91% (CSSD-1 primer) on all the symptomatic cacao leaf samples assessed. The identified CSSD species differed phylogenetically and overlapped in distribution, with the cacao swollen shoot Togo B virus (CSSTBV) (n = 588 sequences) being the most prevalent and widely distributed compared to the other CSSD species that were encountered in both countries. Geographically, the cacao swollen shoot CE virus (CSSCEV) species (n = 124 sequences) that was identified was largely restricted to the bordering regions of Ghana and Côte d’Ivoire. These results provide updated knowledge of the geographic distribution of the key CSSD species and their diagnostic efficiency and, thus, provide guidance in identifying locations for structured testing of cacao germplasm and optimal diagnostics for the predominant CSSD species in Ghana and Côte d’Ivoire.

Analyses of Illumina-based high-throughput sequencing data generated during characterization of the cotton leafroll dwarf virus population in Mississippi (2020–2022) consistently yielded contigs varying in size (most frequently from 4 to 7 kb) with identical nucleotide content and sharing similarities with reverse transcriptases (RTases) encoded by extant plant pararetroviruses (family Caulimoviridiae). Initial data prompted an in-depth study involving molecular and bioinformatic approaches to characterize the nature and origins of these caulimovirid-like sequences. As a result, here, we report on endogenous viral elements (EVEs) related to extant members of the family Caulimoviridae, integrated into a genome of upland cotton (Gossypium hirsutum), for which we propose the provisional name "endogenous cotton pararetroviral elements" (eCPRVE). Our investigations pinpointed a ~15 kbp-long locus on the A04 chromosome consisting of head-to-head orientated tandem copies located on positive- and negative-sense DNA strands (eCPRVE+ and eCPRVE-). Sequences of the eCPRVE+ comprised nearly complete and slightly decayed genome information, including ORFs coding for the viral movement protein (MP), coat protein (CP), RTase, and transactivator/viroplasm protein (TA). Phylogenetic analyses of major viral proteins suggest that the eCPRVE+ may have been initially derived from a genome of a cognate virus belonging to a putative new genus within the family. Unexpectedly, an identical 15 kb-long locus composed of two eCPRVE copies was also detected in a newly recognized species G. ekmanianum, shedding some light on the relatively recent evolution within the cotton family. [ABSTRACT FROM AUTHOR]

The Caulimoviridae is a family of double-stranded DNA viruses that infect plants. The genomes of most vascular plants contain endogenous caulimovirids (ECVs), a class of repetitive DNA elements that is abundant in some plant genomes, resulting from the integration of viral DNA in the chromosomes of germline cells during episodes of infection that have sometimes occurred millions of years ago. In this review, we reflect on 25 years of research on ECVs that has shown that members of the Caulimoviridae have occupied an unprecedented range of ecological niches over time and shed light on their diversity and macroevolution. We highlight gaps in knowledge and prospects of future research fueled by increased access to plant genome sequence data and new tools for genome annotation for addressing the extent, impact, and role of ECVs on plant biology and the origin and evolutionary trajectories of the Caulimoviridae. [ABSTRACT FROM AUTHOR]

To assess the DNA virome associated with air yam (Dioscorea bulbifera L.), leaf samples were collected from plants displaying virus-like symptoms in northeastern Brazil in 2021. Total DNA preparations from PCR positive samples (n = 3) were used as template for viral genome amplification via rolling circle amplification and subjected to high-throughput sequencing. Three Illumina-based full-length badnaviral genomes were recovered from 980 to 30,668 reads and a coverage depth of 33 to 963x. The new genomes ranged from 7,208 to 7,420 bp in size and showed typical badnaviral genomic organization with three main open reading frames (ORFs 1–3). Based on pairwise nucleotide identity using the reverse transcriptase (RT) and ribonuclease H (RNase H) sequences, the newly discovered isolates were identified as dioscorea bacilliform AL virus (DBALV; n = 1) and dioscorea bacilliform SN virus (DBSNV; n = 2), at 85.1–86.6 and 82.2–83.9%, respectively. At least two recombination events were predicted in the DBSNV-DBH isolate, with DBALV- and DBSNV-like sequences identified as putative parents. To our knowledge, these are the first complete genome sequences of yam-infecting badnaviruses described in Brazil. [ABSTRACT FROM AUTHOR]

Abstract Plant, animal and protist genomes often contain endogenous viral elements (EVEs), which correspond to partial and sometimes entire viral genomes that have been captured in the genome of their host organism through a variety of integration mechanisms. While the number of sequenced eukaryotic genomes is rapidly increasing, the annotation and characterization of EVEs remains largely overlooked. EVEs that derive from members of the family Caulimoviridae are widespread across tracheophyte plants, and sometimes they occur in very high copy numbers. However, existing programs for annotating repetitive DNA elements in plant genomes are poor at identifying and then classifying these EVEs. Other than accurately annotating plant genomes, there is intrinsic value in a tool that could identify caulimovirid EVEs as they testify to recent or ancient host-virus interactions and provide valuable insights into virus evolution. In response to this research need, we have developed CAULIFINDER, an automated and sensitive annotation software package. CAULIFINDER consists of two complementary workflows, one to reconstruct, annotate and group caulimovirid EVEs in a given plant genome and the second to classify these genetic elements into officially recognized or tentative genera in the Caulimoviridae. We have benchmarked the CAULIFINDER package using the Vitis vinifera reference genome, which contains a rich assortment of caulimovirid EVEs that have previously been characterized using manual methods. The CAULIFINDER package is distributed in the form of a Docker image.

Eukaryotic genomics frequently revealed historical spontaneous endogenization events of external invading nucleic acids, such as viral elements. In plants, an extensive occurrence of endogenous plant pararetroviruses (EPRVs) is usually believed to endow hosts with an additional layer of internal suppressive weaponry. However, an actual demonstration of this activity remains speculative. We analyzed the EPRV component and accompanying silencing effectors of Solanum lycopersicum , documenting that intronic/intergenic pararetroviral integrations bearing inverted-repeats fuel the plant's RNA-based immune system with suitable transcripts capable of evoking a silencing response. A surprisingly small set of rearrangements explained a substantial fraction of pararetroviral-derived endogenous small-interfering (si)RNAs, enriched in 22-nt forms typically associated with anti-viral post-transcriptional gene silencing. We provide preliminary evidence that such genetic and immunological signals may be found in other species outside the genus Solanum. Based on molecular dating, bioinformatics, and empirical explorations, we propose that homology-dependent silencing emerging from particular immuno-competent rearranged chromosomal areas that constitute an adaptive heritable trans -acting record of past infections, with potential impact against the unlocking of plant latent EPRVs and cognate-free pararetroviruses. [ABSTRACT FROM AUTHOR]

Endogenous viral elements (EVEs) are viral sequences that have been integrated into the nuclear chromosomes. Endogenous pararetrovirus (EPRV) are a class of EVEs derived from DNA viruses of the family Caulimoviridae. Previous works based on a limited number of genome assemblies demonstrated that EPRVs are abundant in plants and are present in several species. The availability of genome sequences has been immensely increased in the recent years and we took advantage of these resources to have a more extensive view of the presence of EPRVs in plant genomes. We analyzed 278 genome assemblies corresponding to 267 species (254 from Viridiplantae) using tBLASTn against a collection of conserved domains of the Reverse Transcriptases (RT) of Caulimoviridae. We concentrated our search on complete and well-conserved RT domains with an uninterrupted ORF comprising the genetic information for at least 300 amino acids. We obtained 11.527 sequences from the genomes of 202 species spanning the whole Tracheophyta clade. These elements were grouped in 57 clusters and classified in 13 genera, including a newly proposed genus we called Wendovirus. Wendoviruses are characterized by the presence of four open reading frames and two of them encode for aspartic proteinases. Comparing plant genomes, we observed important differences between the plant families and genera in the number and type of EPRVs found. In general, florendoviruses are the most abundant and widely distributed EPRVs. The presence of multiple identical RT domain sequences in some of the genomes suggests their recent amplification. [ABSTRACT FROM AUTHOR]

Plant, animal and protist genomes often contain endogenous viral elements (EVEs), which correspond to partial and sometimes entire viral genomes that have been captured in the genome of their host organism through a variety of integration mechanisms. While the number of sequenced eukaryotic genomes is rapidly increasing, the annotation and characterization of EVEs remains largely overlooked. EVEs that derive from members of the family Caulimoviridae are widespread across tracheophyte plants, and sometimes they occur in very high copy numbers. However, existing programs for annotating repetitive DNA elements in plant genomes are poor at identifying and then classifying these EVEs. Other than accurately annotating plant genomes, there is intrinsic value in a tool that could identify caulimovirid EVEs as they testify to recent or ancient host-virus interactions and provide valuable insights into virus evolution. In response to this research need, we have developed CAULIFINDER, an automated and sensitive annotation software package. CAULIFINDER consists of two complementary workflows, one to reconstruct, annotate and group caulimovirid EVEs in a given plant genome and the second to classify these genetic elements into officially recognized or tentative genera in the Caulimoviridae. We have benchmarked the CAULIFINDER package using the Vitis vinifera reference genome, which contains a rich assortment of caulimovirid EVEs that have previously been characterized using manual methods. The CAULIFINDER package is distributed in the form of a Docker image. [ABSTRACT FROM AUTHOR]

Analyses of Illumina-based high-throughput sequencing data generated during characterization of the cotton leafroll dwarf virus population in Mississippi (2020–2022) consistently yielded contigs varying in size (most frequently from 4 to 7 kb) with identical nucleotide content and sharing similarities with reverse transcriptases (RTases) encoded by extant plant pararetroviruses (family Caulimoviridiae). Initial data prompted an in-depth study involving molecular and bioinformatic approaches to characterize the nature and origins of these caulimovirid-like sequences. As a result, here, we report on endogenous viral elements (EVEs) related to extant members of the family Caulimoviridae, integrated into a genome of upland cotton (Gossypium hirsutum), for which we propose the provisional name “endogenous cotton pararetroviral elements” (eCPRVE). Our investigations pinpointed a ~15 kbp-long locus on the A04 chromosome consisting of head-to-head orientated tandem copies located on positive- and negative-sense DNA strands (eCPRVE+ and eCPRVE-). Sequences of the eCPRVE+ comprised nearly complete and slightly decayed genome information, including ORFs coding for the viral movement protein (MP), coat protein (CP), RTase, and transactivator/viroplasm protein (TA). Phylogenetic analyses of major viral proteins suggest that the eCPRVE+ may have been initially derived from a genome of a cognate virus belonging to a putative new genus within the family. Unexpectedly, an identical 15 kb-long locus composed of two eCPRVE copies was also detected in a newly recognized species G. ekmanianum, shedding some light on the relatively recent evolution within the cotton family.

The Caulimoviridae is a family of double-stranded DNA viruses that infect plants. The genomes of most vascular plants contain endogenous caulimovirids (ECVs), a class of repetitive DNA elements that is abundant in some plant genomes, resulting from the integration of viral DNA in the chromosomes of germline cells during episodes of infection that have sometimes occurred millions of years ago. In this review, we reflect on 25 years of research on ECVs that has shown that members of the Caulimoviridae have occupied an unprecedented range of ecological niches over time and shed light on their diversity and macroevolution. We highlight gaps in knowledge and prospects of future research fueled by increased access to plant genome sequence data and new tools for genome annotation for addressing the extent, impact, and role of ECVs on plant biology and the origin and evolutionary trajectories of the Caulimoviridae.

Endogenous viral elements (EVEs) are viral sequences that have been integrated into the nuclear chromosomes. Endogenous pararetrovirus (EPRV) are a class of EVEs derived from DNA viruses of the family Caulimoviridae. Previous works based on a limited number of genome assemblies demonstrated that EPRVs are abundant in plants and are present in several species. The availability of genome sequences has been immensely increased in the recent years and we took advantage of these resources to have a more extensive view of the presence of EPRVs in plant genomes. We analyzed 278 genome assemblies corresponding to 267 species (254 from Viridiplantae) using tBLASTn against a collection of conserved domains of the Reverse Transcriptases (RT) of Caulimoviridae. We concentrated our search on complete and well-conserved RT domains with an uninterrupted ORF comprising the genetic information for at least 300 amino acids. We obtained 11.527 sequences from the genomes of 202 species spanning the whole Tracheophyta clade. These elements were grouped in 57 clusters and classified in 13 genera, including a newly proposed genus we called Wendovirus. Wendoviruses are characterized by the presence of four open reading frames and two of them encode for aspartic proteinases. Comparing plant genomes, we observed important differences between the plant families and genera in the number and type of EPRVs found. In general, florendoviruses are the most abundant and widely distributed EPRVs. The presence of multiple identical RT domain sequences in some of the genomes suggests their recent amplification.

Sweet potato collusive virus (SPCV) is a member of the genus Cavemovirus, family Caulimoviridae, for which only one full-length genome sequence has been reported. SPCV was first detected in Australia in 2007 in two sweet potato accessions using the nitrocellulose membrane ELISA kit developed by the International Potato Centre (CIP). Infected plants were also shown to contain isometric virions of ~ 50 nm, typical of members of the genera Cavemovirus, Caulimovirus, Petuvirus and Soymovirus. We have now sequenced and characterised the complete genomes of the two SPCV isolates (designated SPCV-Aus1 and -Aus2) using a combination of next-generation sequencing and PCR/Sanger sequencing. The sequences of both isolates encode three major ORFs with a genome organisation typical of cavemoviruses. However, isolate SPCV-Aus2 possesses a considerably shorter genome length of 7275 bp compared to SPCV-Aus1 (7712 bp) and the only available full-length sequence from a Portuguese isolate (7723 bp; GenBank accession number NC_015328). Further, ORF 1 of SPCV-Aus2 is considerably shorter than the ORF 1 length of both SPCV-Aus1 and SPCV-Mad1. Phylogenetic and PASC analysis showed that SPCV-Aus1 is closely related to SPCV isolates from North and Central America, whereas SPCV-Aus2 clustered together with isolates from Portugal and Africa. [ABSTRACT FROM AUTHOR]

Sugarcane bacilliform virus (SCBV) is an economically important virus limiting sugarcane production worldwide. Although Ethiopia is a major sugarcane producer, and virus-like symptoms are frequently observed in sugarcane fields, there is a complete lack of information as to the occurrence, distribution and molecular properties of SCBV. This study was aimed to identify and characterize SCBV isolates in Ethiopia using molecular methods. Out of 292 leaf samples collected and tested by PCR, 76 samples (26% incidence level) were found SCBV-positive. Nucleotide sequence analysis results showed that three Ethiopian isolates (SCBV-EtS3, SCBV-EtS6 and SCBV-EtC10) shared high level of nucleotide identity (99.5–100%) among themselves and with SCBV isolates from China (accession numbers MH037614 and MH037915). Another isolate, SCBV-EtC2, shared maximum identity of 78% with the other three SCBV isolates from Ethiopia and 99.8% with SCBV isolates from China (KM214357 and KM214307). Based on phylogenetic analysis, isolates from Ethiopia were segregated into two different clusters. Isolates SCBVEtS3, SCBV-EtS6 and SCBV-EtC10 clustered with SCBV-Q group and SCBV-EtC2 with SCBV-H group. This study provides information on the occurrence of SCBV for the first time in Ethiopia and also contributes to the understanding of the genetic diversity of SCBV. [ABSTRACT FROM AUTHOR]

Aim. The development of an inventory of phytoviruses affecting vegetable and melon crops in the South of the Russian Far East.Discussion. On the basis of many years of original research, carried out on a regular basis by the Laboratory of Virology (Federal Scientific Centre of East Asia Biodiversity, Far Eastern Branch, Russian Academy of Sciences) since 1962 as well as available data in the literature, information about the symptoms of diseases, circulation, reserve plants and vectors are presented for the alfalfa mosaic virus (Bromoviridae, Alfamovirus); tomato aspermy virus and cucumber mosaic virus (Bromoviridae, Cucumovirus); cauliflower mosaic virus (Caulimoviridae, Caulimovirus); garlic mosaic virus (Potyviridae, Carlavirus); tobacco etch virus, allium yellow dwarf virus, bean yellow mosaic virus, watermelon mosaic virus 2, turnip mosaic virus and bean common mosaic virus (Potyviridae, Potyvirus); radish mosaic virus (Picornavirales, Secoviridae, Comovirus); tobacco ringspot virus (Picornavirales, Secoviridae, Nepo-virus); cucumber green mottle mosaic virus, tobacco mosaic virus and tomato mosaic virus (Virgaviridae, Tobamovirus).Conclusion. The information presented forms the basis for the development of a set of diagnostic test systems for phytovirus diseases of vegetable and melon crops; a necessary element of activities directed to the improvement of food productivity and security of the Russian Federation in the Far East.

Cacao swollen shoot disease (CSSD) is a damaging disease of Theobroma cacao L. associated with infection by a group of poorly characterized badnaviral species. To establish causality and characterize the symptomatology associated with infection by the badnavirus cacao swollen shoot Ghana M virus (CSSGMV), an infectious clone (1.3-mer) was constructed and used to inoculated cacao “Amelonado” seedlings by biolistic inoculation (BI; n = 18) and agroinoculation (AI; n = 15). Newly expanded leaves of BI (10/18) and AI (12/15) plants developed foliar mosaic and curling symptoms 30-days post inoculation (dpi), with chlorotic mottling and necrotic crinkling being evident by 90 dpi. By 120 dpi, three of 15 AI plants exhibited characteristic stem-swelling. Viral infection was verified by PCR-amplification and sequencing of a 1068 bp fragment of the CSSGMV ORF3 from newly expanding leaves 60 dpi. The PCR results indicated that 14 of 18 and 15 of 15 BI and AI plants, respectively, were systemically infected. The complete CSSGMV genome sequence was determined, by Illumina sequencing, from representative AI and BI plants and shared >99.5% pairwise nucleotide identity with CSSGMV-Nig9 (GenBank Accession No. MH785299). Based on the development of characteristic CSSD symptoms and recovery of partial and complete genome sequences of CSSGMV-Nig9 from systemically infected cacao plants, Koch's postulates have been fulfilled.

Background and Aims Endogenous pararetroviruses (EPRVs) are widespread components of plant genomes that originated from episomal DNA viruses of the Caulimoviridae family. Due to fragmentation and rearrangements, most EPRVs have lost their ability to replicate through reverse transcription and to initiate viral infection. Similar to the closely related retrotransposons, extant EPRVs were retained and often amplified in plant genomes for several million years. Here, we characterize the complete genomic EPRV fraction of the crop sugar beet (Beta vulgaris , Amaranthaceae) to understand how they shaped the beet genome and to suggest explanations for their absent virulence. Methods Using next- and third-generation sequencing data and genome assembly, we reconstructed full-length in silico representatives for the three host-specific EPRVs (beetEPRVs) in the B. vulgaris genome. Focusing on the endogenous caulimovirid beetEPRV3, we investigated its chromosomal localization, abundance and distribution by fluorescent in situ and Southern hybridization. Key Results Full-length beetEPRVs range between 7.5 and 10.7 kb in size, are heterogeneous in structure and sequence, and occupy about 0.3 % of the beet genome. Although all three beetEPRVs were assigned to the florendoviruses, they showed variably arranged protein-coding domains, different fragmentation, and preferences for diverse sequence contexts. We observed small RNAs that specifically target the individual beetEPRVs, indicating stringent epigenetic suppression. BeetEPRV3 sequences occur along all sugar beet chromosomes, preferentially in the vicinity of each other and are associated with heterochromatic, centromeric and intercalary satellite DNAs. BeetEPRV3 members also exist in genomes of related wild species, indicating an initial beetEPRV3 integration 13.4–7.2 million years ago. Conclusions Our study in beet illustrates the variability of EPRV structure and sequence in a single host genome. Evidence of sequence fragmentation and epigenetic silencing implies possible plant strategies to cope with long-term persistence of EPRVs, including amplification, fixation in the heterochromatin, and containment of EPRV virulence. [ABSTRACT FROM AUTHOR]

Although chestnut mosaic disease (ChMD) was described several decades ago, its etiology is still not clear. Using classical approaches and highthroughput sequencing (HTS) techniques, we identified a novel Badnavirus that is a strong etiological candidate for ChMD. Two disease sources from Italy and France were submitted to HTS-based viral indexing. Total RNAs were extracted, ribodepleted, and sequenced on an Illumina NextSeq500 (2 × 150 nt or 2 × 75 nt). In each source, we identified a single contig of -7.2 kb that corresponds to a complete circular viral genome and shares homologies with various badnaviruses. The genomes of the two isolates have an average nucleotide identity of 90.5%, with a typical badnaviral genome organization comprising three open reading frames. Phylogenetic analyses and sequence comparisons showed that this virus is a novel species; we propose the name Chestnut mosaic virus (ChMV). Using a newly developed molecular detection test, we systematically detected the virus in symptomatic graft-inoculated indicator plants (chestnut and American oak) as well in chestnut trees presenting typical ChMD symptoms in the field (100 and 87% in France and Italy surveys, respectively). Datamining of publicly available chestnut sequence read archive transcriptomic data allowed the reconstruction of two additional complete ChMV genomes from two Castanea mollissima sources from the United States as well as ChMV detection in C. dentata from the United States. Preliminary epidemiological studies performed in France and central eastern Italy showed that ChMV has a high incidence in some commercial orchards and low within-orchard genetic diversity. [ABSTRACT FROM AUTHOR]

Theobroma cacao is one of the most economically important tropical trees, being the source of chocolate. As part of an ongoing study to understand the diversity of the badnavirus complex, responsible for the cacao swollen shoot virus disease in West Africa, evidence was found recently of virus-like sequences in asymptomatic cacao plants. The present study exploited the wealth of genomic resources in this crop, and combined bioinformatic, molecular, and genetic approaches to report for the first time the presence of integrated badnaviral sequences in most of the cacao genetic groups. These sequences, which we propose to name eTcBV for endogenous T. cacao bacilliform virus, varied in type with each predominating in a specific genetic group. A diagnostic multiplex PCR method was developed to identify the homozygous or hemizygous condition of one specific insert, which was inherited as a single Mendelian trait. These data suggest that these integration events occurred before or during the species diversification in Central and South America, and prior to its cultivation in other regions. Such evidence of integrated sequences is relevant to the management of cacao quarantine facilities and may also aid novel methods to reduce the impact of such viruses in this crop. [ABSTRACT FROM AUTHOR]

Badnaviruses are plant pararetroviruses that infect economically important crops worldwide, and several badnaviral species have been reported causing significant economic losses in cacao plantations in West Africa. Based on the available full-length genome sequences of cacao swollen shoot disease (CSSD)-associated badnaviruses (n = 66), four primer pairs (CSSD1-CSSD4) were designed to amplify a fragment of the 5′ region of open reading frame (ORF) 3, which comprises the movement protein, by polymerase chain reaction (PCR). Primers were evaluated for their ability to amplify a badnaviral fragment(s) from symptomatic and asymptomatic cacao leaf samples collected in Côte d'Ivoire during 2017–2019. The PCR products obtained by amplification with the CSSD1 primers showed high sequence variability and were phylogenetically related to one of three different badnaviral species, Cacao swollen shoot Togo B virus, Cacao swollen shoot CD virus, and Cacao swollen shoot CE virus, while the CSSD2 and CSSD4 amplicon sequences grouped exclusively with either cacao swollen shoot Togo B virus (CSSTBV) and Cacao swollen shoot Ghana M virus isolates, respectively. The majority of the isolates obtained here were most closely phylogenetically related to CSSTBV, with which they shared 81.0–98.0% nucleotide identity, making the CSSTBV-like isolates the predominant species associated with badnavirus-infected cacao trees tested in Côte d'Ivoire. [ABSTRACT FROM AUTHOR]

Abstract Background A disease of unknown etiology in water chestnut plants (Eleocharis dulcis) was reported in China between 2012 and 2014. High throughput sequencing of small RNA (sRNA) combined with bioinformatics, and molecular identification based on PCR detection with virus-specific primers and DNA sequencing is a desirable approach to identify an unknown infectious agent. In this study, we employed this approach to identify viral sequences in water chestnut plants and to explore the molecular interaction of the identified viral pathogen and its natural plant host. Results Based on high throughput sequencing of virus-derived small RNAs (vsRNA), we identified the sequence a new-to-science double-strand DNA virus isolated from water chestnut cv. ‘Tuanfeng’ samples, a widely grown cultivar in Hubei province, China, and analyzed its genomic organization. The complete genomic sequence is 7535 base-pairs in length, and shares 42–52% nucleotide sequence identity with viruses in the Caulimoviridae family. The virus contains nine predicated open reading frames (ORFs) encoding nine hypothetical proteins, with conserved domains characteristic of caulimoviruses. Phylogenetic analyses at the nucleotide and amino acid levels indicated that the virus belongs to the genus Soymovirus. The virus is tentatively named Water chestnut soymovirus-1 (WCSV-1). Phylogenetic analysis of the putative viral polymerase protein suggested that WCSV-1 is distinct to other well established species in the Soymovirus genus. This conclusion was supported by phylogenetic analyses of the amino acid sequences encoded by ORFs I, IV, VI, or VII. The sRNA bioinformatics showed that the majority of the vsRNAs are 22-nt in length with a preference for U at the 5′-terminal nucleotide. The vsRNAs are unevenly distributed over both strands of the entire WCSV-1 circular genome, and are clustered into small defined regions. In addition, we detected WCSV-1 in asymptomatic and symptomatic water chestnut samples collected from different regions of China by using PCR. RNA-seq assays further confirmed the presence of WCSV-1-derived viral RNA in infected plants. Conclusions This is the first discovery of a dsDNA virus in the genus Soymovirus infecting water chestnuts. Data presented also add new information towards a better understanding of the co-evolutionary mechanisms between the virus and its natural plant host.

Sweet potato is among the most important root crops worldwide, particularly in developing countries, and its production is affected severely by a variety of virus diseases. During the last decade, a number of new viruses have been discovered in sweet potatoes through next-generation sequencing studies. Among them are viruses belonging to the genus Badnavirus and collectively assigned to the species sweet potato pakakuy virus (SPPV). We determined the complete genome sequence of two SPPV isolates and show the ubiquitous presence of similar viruses in germplasm and field material from around the globe. We show that SPPV is not integrated into the sweet potato genome, occurs only at extremely low titers, and is efficiently transmitted through seeds and cuttings. They are unaffected by virus elimination therapy and do not induce discernible symptoms in sweet potatoes or indicator host plants. They show considerable variation in their nucleotide sequences and correspond to several genetic lineages. Studies of their interaction with the two most important sweet potato viruses showed only limited synergistic increase in the titers of one of two SPPV isolates. We contend that these viruses may pose little threat to sweet potato production and more likely represent a new type of persistent virus in sweet potato.

Sweet potato is among the most important root crops worldwide, particularly in developing countries, and its production is affected severely by a variety of virus diseases. During the last decade, a number of new viruses have been discovered in sweet potatoes through next-generation sequencing studies. Among them are viruses belonging to the genus Badnavirus and collectively assigned to the species sweet potato pakakuy virus (SPPV). We determined the complete genome sequence of two SPPV isolates and show the ubiquitous presence of similar viruses in germplasm and field material from around the globe. We show that SPPV is not integrated into the sweet potato genome, occurs only at extremely low titers, and is efficiently transmitted through seeds and cuttings. They are unaffected by virus elimination therapy and do not induce discernible symptoms in sweet potatoes or indicator host plants. They show considerable variation in their nucleotide sequences and correspond to several genetic lineages. Studies of their interaction with the two most important sweet potato viruses showed only limited synergistic increase in the titers of one of two SPPV isolates. We contend that these viruses may pose little threat to sweet potato production and more likely represent a new type of persistent virus in sweet potato. [ABSTRACT FROM AUTHOR]

Dahlia mosaic virus (DMV), an aphid‐transmitted caulimovirus in the family Caulimoviridae, is an important pathogen of dahlia (Dahlia variabilis). Development of rapid, and sensitive diagnostic tools is essential in surveillance and management of DMV. A loop‐mediated isothermal amplification (LAMP) assay was developed for DMV detection. The LAMP assay targets the reverse transcriptase region of the DMV genome and is optimal at a temperature of 60°C and run time of 60 min, and amplification was detected through fluorescence detection and by agarose gel electrophoresis. The assay detected DMV in DNA concentration as low as 10−3 ng. To the best of our knowledge, this is the first report of a LAMP assay for the detection of DMV, a plant DNA virus. This assay will be useful in rapid and sensitive detection of DMV and in reducing the virus incidence through production of virus‐free planting material. [ABSTRACT FROM AUTHOR]

Petunia plants are used for urban landscaping in many parts of the world, including South Korea. In this study, we aimed to investigate the occurrence of petunia vein clearing virus (PVCV) infection in petunia plants in Seoul, South Korea. PVCV was detected from 23 of 79 petunia samples collected from Seoul. We obtained the complete genome sequences of the Korean isolates in this study (called PVCV-Kr, Kr2, and Kr3), which were compared with the genome sequence of the USA isolate of the virus (PVCV-USA). The genomic DNA of the three PVCV isolates was found to comprise 7210–7267 nucleotides (nts), which is 4–15 nts longer than the PVCV-USA genome. The genomes of the Kr and Kr2 isolates encode a large polyprotein of 252 kDa (2180 amino acids (aa)). The genome of the Kr3 isolate encodes a large polyprotein of 255 kDa (2203 aa). The polyprotein has six protein domains: a movement protein (MP; 72 aa), a coiled-coil domain (CC; 33 aa), an RNA-binding domain (RB; 18 aa), a protease (PR; 21 aa), a reverse transcriptase (RT; 196 aa), and an RNase H (RH; 121 aa). The large polyprotein and six domains of the three isolates showed 93.9–100.0% sequence homology with those of PVCV-USA. Furthermore, the polymerase polyprotein gene (PR, RT, and RH) of the four PVCV isolates containing the USA isolate grouped with those of Rice tungro bacilliform virus and Soybean chlorotic mottle virus, which belong to the same family (Caulimoviridae). Our findings suggested that the Korean isolates represent a new isolate of PVCV. To our knowledge, this is the first report of PVCV detection in South Korea. [ABSTRACT FROM AUTHOR]

Abstract Background Cacao swollen shoot virus (CSSV), Cacao swollen shoot CD virus (CSSCDV), and Cacao swollen shoot Togo A virus (CSSTAV) cause cacao swollen shoot disease (CSSD) in West Africa. During 2000–2003, leaf and shoot-swelling symptoms and rapid tree death were observed in cacao in Cote d’Ivoire and Ghana. Molecular tests showed positive infection in only ~50–60% of symptomatic trees, suggesting the possible emergence of an unknown badnavirus. Methods The DNA virome was determined from symptomatic cacao samples using Illumina-Hi Seq, and sequence accuracy was verified by Sanger sequencing. The resultant 14, and seven previously known, full-length badnaviral genomic and RT-RNase H sequences were analyzed by pairwise distance analysis to resolve species relationships, and by Maximum likelihood (ML) to reconstruct phylogenetic relationships. The viral coding and non-coding sequences, genome organization, and predicted conserved protein domains (CPDs) were identified and characterized at the species level. Results The 21 CSSD-badnaviral genomes and RT-RNase H sequences shared 70–100% and 72–100% identity, respectively. The RT-RNase H analysis predicted four species, based on an ≥80% species cutoff. The ML genome sequence tree resolved three well-supported clades, with ≥70% bootstrap, whereas, the RT-RNase H phylogeny was poorly resolved, however, both trees grouped CSSD isolates within one large clade, including the newly discovered Cacao red vein virus (CRVV) proposed species. The genome arrangement of the four species consists of four, five, or six predicted open reading frames (ORFs), and the CPDs have similar architectures. By comparison, two New World cacao-infecting badnaviruses encode four ORFs, and harbor CPDs like the West African species. Conclusions Three previously recognized West African cacao-infecting badnaviral species were identified, and a fourth, previously unidentified species, CRVV, is described for the first time. The CRVV is a suspect causal agent of the rapid decline phenotype, however Koch’s Postulates have not been proven. To reconcile viral evolutionary with epidemiology considerations, more detailed information about CSSD-genomic variability is essential. Also, the functional basis for the multiple genome arrangements and subtly distinct CPD architectures among cacao-infecting badnaviruses is poorly understood. New knowledge about functional relationships may help explain the diverse symptomatologies observed in affected cacao trees.

We have characterized the complete genome sequence of an Australian isolate of banana streak CA virus (BSCAV). A greater-than-full-length, cloned copy of the virus genome was assembled and agroinoculated into five tissue-cultured plants of nine different Musa acuminata banana accessions. BSCAV was highly infectious in all nine accessions. All five inoculated plants from eight accessions developed symptoms by 28 weeks post-inoculation, while all five plants of M. acuminata AA subsp. zebrina remained symptomless. Symptoms were mild in six accessions but were severe in Khae Phrae (M. acuminata subsp. siamea) and the East African Highland banana accession Igisahira Gisanzwe. This is the first full-length BSCAV genome sequence reported from Australia and the first report of the infectivity of an infectious clone of banana streak virus.

Taro (Colocasia esculenta) and tannia (Xanthosoma sp.) are important root crops cultivated mainly by small‐scale farmers in sub‐Saharan Africa and the South Pacific. Viruses are known to be one of the most important constraints to production, with infections resulting in severe yield reduction. In 2014 and 2015, surveys were conducted in Ethiopia, Kenya, Tanzania and Uganda to determine the identity of viruses infecting taro in East Africa. Screening of 392 samples collected from the region using degenerate badnavirus primers revealed an incidence of 58–74% among the four countries surveyed, with sequence analysis identifying both Taro bacilliform virus (TaBV) and Taro bacilliform CH virus (TaBCHV). TaBCHV was identified from all four countries while TaBV was identified in all except Ethiopia. Full‐length sequences from representative TaBV and TaBCHV isolates showed that the genome organization of TaBV isolates from East Africa was consistent with previous reports while TaBCHV isolates from East Africa were found to encode only four ORFs, distinct from a previous report from China. Phylogenetic analysis showed that all East African TaBV isolates form a single subgroup within known TaBV isolates, while TaBCHV isolates form at least two distinct subgroups. To the authors' knowledge, this is the first report describing the occurrence and genome organization of TaBV and TaBCHV isolates from East Africa and the first full‐length sequence of the two viruses from tannia. [ABSTRACT FROM AUTHOR]

The incidence of cacao swollen shoot disease (CSSD) in cacao (Theobroma cacao L.) has increased in West Africa since ~2000. To investigate the genomic and species diversity of the CSSD-badnaviruses infecting cacao in Côte d’Ivoire and Ghana, symptomatic leaves were subjected to high-throughput sequencing. Among the 30 newly determined genomes, three badnaviruses were identified, Cacao swollen shoot Togo B virus (CSSTBV), Cacao swollen shoot CD virus, and Cacao swollen shoot CE virus (CSSCEV). The phylogenetic trees reconstructed for the reverse transcriptase (RT) and ribonuclease H (RNase H) sequences were incongruent with the complete viral genomes, which had the most robust statistical support. Recombination seems to be involved in the CSSD-badnavirus diversification. The genomic diversity varied among different CSSD-badnaviruses, with CSSTBV showing the lowest nucleotide diversity (π = 0.06236), and CSSCEV exhibiting the greatest variability (π = 0.21911). Evidence of strong purifying selection was found in the coding regions of the CSSTBV isolates.

Here, we report the genome sequence and evidence for transcriptional activity of a virus-like element in the native Chilean berry tree Aristotelia chilensis. We propose to name the endogenous sequence as Aristotelia chilensis Virus 1 (AcV1). High-throughput sequencing of the genome of this tree uncovered an endogenous viral element, with a size of 7122 bp, corresponding to the complete genome of AcV1. Its sequence contains three open reading frames (ORFs): ORFs 1 and 2 shares 66%–73% amino acid similarity with members of the Caulimoviridae virus family, especially the Petunia vein clearing virus (PVCV), Petuvirus genus. ORF1 encodes a movement protein (MP); ORF2 a Reverse Transcriptase (RT) and a Ribonuclease H (RNase H) domain; and ORF3 showed no amino acid sequence similarity with any other known virus proteins. Analogous to other known endogenous pararetrovirus sequences (EPRVs), AcV1 is integrated in the genome of Maqui Berry and showed low viral transcriptional activity, which was detected by deep sequencing technology (DNA and RNA-seq). Phylogenetic analysis of AcV1 and other pararetroviruses revealed a closer resemblance with Petuvirus. Overall, our data suggests that AcV1 could be a new member of Caulimoviridae family, genus Petuvirus, and the first evidence of this kind of virus in a fruit plant.

We have characterized the complete genome of a novel circular double-stranded DNA virus, tentatively named Dioscorea nummularia-associated virus (DNUaV), infecting Dioscorea nummularia originating from Samoa. The genome of DNUaV comprised 8139 bp and contained four putative open reading frames (ORFs). ORFs 1 and 2 had no identifiable conserved domains, while ORF 3 had conserved motifs typical of viruses within the family Caulimoviridae including coat protein, movement protein, aspartic protease, reverse transcriptase and ribonuclease H. A transactivator domain, similar to that present in members of several caulimoviridae genera, was also identified in the putative ORF 4. The genome size, organization, and presence of conserved amino acid domains are similar to other viruses in the family Caulimoviridae. However, based on nucleotide sequence similarity and phylogenetic analysis, DNUaV appears to be a distinct novel member of the family and may represent a new genus. [ABSTRACT FROM AUTHOR]

Endogenous viral elements (paleoviruses) provide "molecular fossils" for studying the deep history and macroevolution of viruses. Endogenous plant pararetroviruses (EPRVs) are widespread in angiosperms, but little is known about EPRVs in earlier-branching plants. Here we use a large-scale phylogenomic approach to investigate the diversity and macroevolution of plant pararetroviruses (formally known as Caulimoviridae). We uncover an unprecedented and unappreciated diversity of EPRVs within the genomes of gymnosperms and ferns. The known angiosperm viruses constitute only a minor part of the Caulimoviridae diversity. By characterizing the distribution of EPRVs, we show that no major euphyllophyte lineages escape the activity of Caulimoviridae, raising the possibility that many exogenous Caulimoviridae remain to be discovered in euphyllophytes. We find that the copy numbers of EPRVs are generally high, suggesting that EPRVs might define a unique group of repetitive elements and represent important components of euphyllophyte genomes. Evolutionary analyses suggest an ancient origin of Caulimoviridae and at least three independent origins of Caulimoviridae in angiosperms. Our findings reveal the remarkable diversity of Caulimoviridae and have important implications for understanding the origin and macroevolution of plant pararetroviruses. [ABSTRACT FROM AUTHOR]

In declining birches (Betula sp.) from different European stands affected by the “birch leaf-roll disease” (BLRD) a novel virus is identified by means of RNA-Seq virome analysis. The virus represents a new member in the genus Badnavirus, family Caulimoviridae, tentatively named Birch leaf roll-associated virus (BLRaV) and it is the first badnavirus found to infect birch. Complete genome sequences (7,862–7,864 nucleotides) of three viral isolates of Finnish and German origin have been determined. The virus sequences show a typical badnavirus organization with three major open reading frames (ORFs) and a fourth potential ORF overlapping with the end of ORF3. ORFs 1-2-3 show low level of amino acid identity to the corresponding proteins encoded by other badnaviruses, reaching a maximum of 44% identity (ORF3). Grapevine vein-clearing virus appears as the closest badnavirus when considering the polymerase region. So far, we can exclude evidence for presence of endogenous BLRaV elements in the birch genome, while evidence for the episomal activity of BLRaV is provided. The viral population holds significant haplotype diversity, while co-infection by different BLRaV variants are observed in single hosts. BLRaV presence is associated with the BLRD in both silver (B. pendula) and downy birch (B. pubescens). These results challenge the earlier hypothesis of a causal role of Cherry leaf roll virus in BLRD. Further work is now needed to finally prove that BLRaV is the causal agent for the BLRD. [ABSTRACT FROM AUTHOR]

Cacao swollen shoot virus is a member of the family Caulimoviridae , genus Badnavirus and is naturally transmitted to Theobroma cacao (L.) by several mealybug species. CSSV populations in West African countries are highly variable and genetically structured into several different groups based on the diversity in the first part of ORF3 which encodes the movement protein. To unravel the extent of isolate diversity and address the problems of low titer and mixed viral sequences in samples, we used Illumina MiSeq and HiSeq technology. We were able to reconstruct de novo 20 new complete genomes from cacao samples collected in the Cocoa Research Institute of Ghana (CRIG) Museum and from the field samples collected in Côte d’Ivoire or Ghana. Based on the 20% threshold of nucleotide divergence in the reverse transcriptase/ribonuclease H (RT/RNase H) region which denotes species demarcation, we conclude there exist seven new species associated with the cacao swollen shoot disease. These new species along with the three already described leads to ten, the total number of the complex of viral species associated with the disease. A sample from Sri Lanka exhibiting similar leaf symptomology to West African CSSD-affected plants was also included in the study and the corresponding sequence represents the genome of a new virus named cacao bacilliform SriLanka virus (CBSLV). [ABSTRACT FROM AUTHOR]

Members of the genus Badnavirus have a single non-covalently closed circular double-stranded DNA genome of 7.2–9.2 kb. The genome encodes three open reading frames (ORFs) on the positive DNA strand. Canna yellow mottle virus (CaYMV) is a badnavirus that has been described as the etiological cause of yellow mottle disease in canna, although only a 565 bp fragment of the genome has been previously reported from cannas. In this report, concentrated virions were recovered from infected canna plants and nucleic acids were extracted. Two full-length sequences represent two badnavirus genomes were recovered and were determined to be 6966 bp and 7385 bp in length. These DNAs represent a virus strain belonging to Canna yellow mottle virus and a novel species tentatively termed Canna yellow mottle associated virus. Phylogenetic analysis indicates that these two viruses are closely related to sugarcane bacilliform GD virus, pineapple bacilliform comosus virus, banana streak MY virus, and cycad leaf necrosis virus. We also showed naturally grown canna plants to be frequently co-infected by these two badnaviruses along with a potyvirus, Canna yellow streak virus . [ABSTRACT FROM AUTHOR]

Background: Cacao swollen shoot virus (CSSV), Cacao swollen shoot CD virus (CSSCDV), and Cacao swollen shoot Togo A virus (CSSTAV) cause cacao swollen shoot disease (CSSD) in West Africa. During 2000-2003, leaf and shoot-swelling symptoms and rapid tree death were observed in cacao in Cote d'Ivoire and Ghana. Molecular tests showed positive infection in only ~50-60% of symptomatic trees, suggesting the possible emergence of an unknown badnavirus. Methods: The DNA virome was determined from symptomatic cacao samples using Illumina-Hi Seq, and sequence accuracy was verified by Sanger sequencing. The resultant 14, and seven previously known, full-length badnaviral genomic and RT-RNase H sequences were analyzed by pairwise distance analysis to resolve species relationships, and by Maximum likelihood (ML) to reconstruct phylogenetic relationships. The viral coding and non-coding sequences, genome organization, and predicted conserved protein domains (CPDs) were identified and characterized at the species level. Results: The 21 CSSD-badnaviral genomes and RT-RNase H sequences shared 70-100% and 72-100% identity, respectively. The RT-RNase H analysis predicted four species, based on an ⩾80% species cutoff. The ML genome sequence tree resolved three well-supported clades, with ⩾70% bootstrap, whereas, the RT-RNase H phylogeny was poorly resolved, however, both trees grouped CSSD isolates within one large clade, including the newly discovered Cacao red vein virus (CRVV) proposed species. The genome arrangement of the four species consists of four, five, or six predicted open reading frames (ORFs), and the CPDs have similar architectures. By comparison, two New World cacao-infecting badnaviruses encode four ORFs, and harbor CPDs like the West African species. Conclusions: Three previously recognized West African cacao-infecting badnaviral species were identified, and a fourth, previously unidentified species, CRVV, is described for the first time. The CRVV is a suspect causal agent of the rapid decline phenotype, however Koch's Postulates have not been proven. To reconcile viral evolutionary with epidemiology considerations, more detailed information about CSSD-genomic variability is essential. Also, the functional basis for the multiple genome arrangements and subtly distinct CPD architectures among cacaoinfecting badnaviruses is poorly understood. New knowledge about functional relationships may help explain the diverse symptomatologies observed in affected cacao trees. [ABSTRACT FROM AUTHOR]

Long terminal repeat retrotransposons represent a major component of plant genomes and act as drivers of genome evolution and diversity. Musa is an important fruit crop and also used as a starchy vegetable in many countries. BAC sequence analysis by dot plot was employed to investigate the LTR retrotransposons from Musa genomes. Fifty intact LTR retrotransposons from selected Musa BACs were identified by dot plot analysis and further BLASTN searches retrieved 153 intact copies, 61 truncated, and a great number of partial copies/remnants from GenBank database. LARD-like elements were also identified with several copies dispersed among the Musa genotypes. The predominant elements were the LTR retrotransposons Copia and Gypsy, while Caulimoviridae (pararetrovirus) were rare in the Musa genome. PCR amplification of reverse transcriptase (RT) sequences revealed their abundance in almost all tested Musa accessions and their ancient nature before the divergence of Musa species. The phylogenetic analysis based on RT sequences of Musa and other retrotransposons clustered them into Gypsy, Caulimoviridae, and Copia lineages. Most of the Musa-related elements clustered in their respective groups, while some grouped with other elements indicating homologous sequences. The present work will be helpful to understand the LTR retrotransposons landscape, giving a complete picture of the nature of the elements, their structural features, annotation, and evolutionary dynamics in the Musa genome. [ABSTRACT FROM AUTHOR]

We report a new circular DNA virus identified from a Chinese jujube tree showing mosaic-like symptoms. The genome of this virus is 7194 bp in length and contains five putative open reading frames (ORFs), all on the plus-strand of the genome. The genomic organization, primer binding sites and the sizes of the ORFs were similar to those reported for other badnaviruses (family Caulimoviridae), except for ORF3, which was split into ORF3a and ORF3b with a 70-nt intergenic region. Furthermore, this new virus shares low nucleotide sequence identity (<50%) with other members of the family Caulimoviridae. Consequently, we propose this virus as a new member of the family Caulimoviridae and refer to it as jujube mosaic-associated virus (JuMaV). [ABSTRACT FROM AUTHOR]

A disease of Rudbeckia hirta (Black-eyed Susan), characterized by severe flower deformation, was observed in Minnesota during 2010–2016. A previously undescribed virus species, named Rudbeckia flower distortion virus (RuFDV, family Caulimoviridae , genus unassigned), was determined to be the causal agent of the disease. Symptoms induced by RuFDV infection resemble those characteristic of phytoplasma-induced diseases, but no phytoplasmas were detected in RuFDV-infected R. hirta . The virus, and the disease were transmitted readily by mechanical inoculation and by the aphid Myzus persicae , but only to R. hirta . Virions of RuFDV are icosahedral, 42–45 nm in diameter, and contain a circular 8222 bp dsDNA genome containing seven open reading frames (ORFs). The ORFs 2–6 have 28–52% amino acid sequence identity to the movement protein (MP), coat protein (CP), aspartic protease (AP), reverse transcriptase (RT) and RNase H, and translational transactivator (TA) domains of known caulimoviruses. The two remaining ORFs (1 and 7) have no significant amino acid sequence similarity to known viruses. Although the RuFDV ORF 6 is significantly truncated relative to those of other known caulimoviruses, neither this nor the concomitant absence of characteristic virus-encoded cytoplasmic inclusion bodies appears to adversely affect aphid transmission of this virus. Phylogenetic analysis based on the sequence of the RT region revealed no close relationship to known members of the family Caulimoviridae . Based on sequence similarity, genome organization and phylogenetic relatedness, RuFDV appears to be distinct from any currently recognized taxonomic grouping in the family Caulimoviridae. [ABSTRACT FROM AUTHOR]

Badnaviruses (family Caulimoviridae, genus Badnavirus) have emerged as serious pathogens especially affecting the cultivation of tropical crops. Badnavirus sequences can be integrated in host genomes, complicating the detection of episomal infections and the assessment of viral genetic diversity in samples containing a complex mixture of sequences. Yam (Dioscorea spp.) plants are hosts to a diverse range of badnavirus species, and recent findings have suggested that mixed infections occur frequently in West African yam germplasm. Historically, the determination of the diversity of badnaviruses present in yam breeding lines has been achieved by cloning and sequencing of polymerase chain reaction (PCR) products. In this study, the molecular diversity of partial reverse transcriptase (RT)-ribonuclease H (RNaseH) sequences from yam badnaviruses was analysed using PCR-dependent denaturing gradient gel electrophoresis (PCR-DGGE). This resulted in the identification of complex 'fingerprints' composed of multiple sequences of Dioscorea bacilliform viruses (DBVs). Many of these sequences show high nucleotide identities to endogenous DBV (eDBV) sequences deposited in GenBank, and fall into six monophyletic species groups. Our findings highlight PCR-DGGE as a powerful tool in badnavirus diversity studies enabling a rapid indication of sequence diversity as well as potential candidate integrated sequences revealed by their conserved nature across germplasm. [ABSTRACT FROM AUTHOR]

The complete sequence of a strawberry vein banding virus (SVBV) isolate collected in Nova Scotia, Canada, and designated NS8, was determined. The 7,856-nucleotide circular double-stranded DNA genome contains seven open-reading frames (ORFs), which is consistent with other SVBV isolates and other members of the genus Caulimovirus. Comparison of NS8 with other whole-genome sequences retrieved from databases revealed that NS8 shares the highest sequence similarity (96.5% identity) with isolate China (accession number HE681085) and the lowest (88.3% identity) with clone pSVBV-E3 (accession number X97304). Despite the overall high sequence similarity between NS8 and China, the coat protein encoding ORF IV of NS8 shares only 90.9% sequence identity with the China isolate. Phylogenetic analysis at the complete-genome level placed NS8 and all Chinese isolates in one clade and clone pSVBV-E3 in a separate clade. Interestingly, phylogenetic analysis of all available ORF IV sequences, including those retrieved from databases and newly sequenced samples in this study from Canada, revealed three distinct clades. All Canadian isolates grouped together as one clade, pSVBV-E3 and several others from Europe, Egypt and the USA grouped as a second clade, and isolates from China formed a third clade. These results demonstrate that SVBV is more divergent than previously reported. [ABSTRACT FROM AUTHOR]

Polyomaviruses (PyVs), belonging to the family Polyomaviridae, are a group of small, nonenveloped, double-stranded, circular DNA viruses widely distributed in the vertebrates. PyVs cause no apparent disease in adult laboratory mice but cause a wide variety of tumors when artificially inoculated into neonates or semipermissive animals. A few human PyVs, such as BK, JC, and Merkel cell PyVs, have been unequivocally linked to pathogenesis under conditions of immunosuppression. Infection is thought to occur early in life and persists for the lifespan of the host. Over evolutionary time scales, it appears that PyVs have slowly co-evolved with specific host animal lineages. Host cell surface glycoproteins and glycolipids seem to play a decisive role in the entry stage of viral infection and in channeling the virions to specific intracellular membrane-bound compartments and ultimately to the nucleus, where the genomes are replicated and packaged for release. Therefore the transport of the infecting virion or viral genome to this site of multiplication is an essential process in productive viral infection as well as in latent infection and transformation. This review summarizes the major findings related to the characterization of the nature of the interactions between PyV and host protein and their impact in host cell invasion. [ABSTRACT FROM AUTHOR]

Grapevine vein clearing virus (GVCV), a new member of the genus Badnavirus in the family Caulimoviridae, is associated with a vein clearing and vine decline disease that severely affects grape production and berry quality in commercial vineyards in the Midwest region of the United States. In this paper, the genetic and phenotypic characteristics of GVCV-VRU1 and GVCV-VRU2, two isolates from wild Vitis rupestris grapevines in their native habitat, are described. The GVCV-VRUI genome is 7,755 bp long while the GVCV-VRU2 genome consists of 7,725 bp, both of which are different from the genome of the GVCV-CHA isolate (7,753 bp), which was originally discovered in the grape cultivar 'Chardonel'. The nucleotide sequence identity among GVCV-VRU I. GVCV-VRU2, and GVCV-CHA ranges from 91.6 to 93.4%, and open reading frame (ORF) II is the most divergent ORF with only 83.3 to 88.5% identity. Sequence analysis of the ORF II indicated that GVCV isolates genetically similar to GVCV-VRU 1 and GVCV-VRU2 also are present in commercial vineyards. Symptoms of GVCV-VRU 1- or GVCV-VRU2-infected wild V. rupestris grapevine appeared initially as translucent vein clearing on young leaves and progressed to vein necrosis on mature leaves. Inoculation of GVCV-VRU I or GVCV-VRU2 by grafting onto grape cultivar Chardonel resulted in mild mottle and leaf distortion. The natural range of wild V. rupestris grapevines overlaps with commercial vineyards in the Midwestern United States. Therefore, the discovery of GVCV isolates in wild V. rupestris grapevines has important implications for epidemics and management of the GVCV-associated disease. [ABSTRACT FROM AUTHOR]

Blackberry viruses are pervasive, decreasing growth, yield, and plant longevity. In a quest to identify viruses associated with blackberry yellow vein, a disease caused by virus complexes, a new double-stranded DNA virus, referred to as blackberry virus F (BVF), a putative member of the genus Badnavirus, family Caulimoviridae, was identified. The virus was found in both cultivated and wild blackberry samples collected from several states in the southern United States. Population structure, host range, and association with disease symptoms were assessed. As BVF integrates into the plant genome, it affects the production of virus-free propagation material, the cornerstone for certification programs. [ABSTRACT FROM AUTHOR]

This study describes the nucleotide sequence and genome organization of a new DNA virus isolated from 'Bluecrop' blueberry plants exhibiting fruit-drop symptoms and named Blueberry fruit drop-associated virus (BFDaV). Blueberry fruit drop disease was first detected in blueberry plants in British Columbia. Canada in the late 1990s, and in a single field in northern Washington state in the United States in 2012. Infected bushes abort nearly 100% of their fruit about three weeks prior to harvest, when the berries are about 3 to 5 mm in diameter. At harvest, the affected plants appear taller than healthy ones as there is no fruit weighing down the branches. The virus was amplified from diseased material using rolling circle amplification, followed by enzyme digestion, cloning, and sequencing. The full genome of BFDaV is 9,850 bp in length and contains a single open reading frame, encoding for a polyprotein, and a large noncoding region. Based on the genome size and organization and phylogenetics, BFDaV is proposed as a new and the largest member of family Caulimoviridae. Finally, in mapping part of a field with fruit-drop symptoms, there was a nearly perfect correlation between the presence of the virus and fruit-drop symptoms. [ABSTRACT FROM AUTHOR]

Cynodon dactylon and Zoysia japonica are two important warm-season turfgrass species with multiple utilizations. Genetic transformations of Cynodon dactylon and Zoysia japonica are extremely difficult, which severely restrict the gene functional studies and molecular breeding research of the two grasses. By contrast, virus-induced gene silencing (VIGS) presents an effective and rapid alternative method to create targeted gene knock-outs for gene functional studies in plants. In this study, we tested the efficiency of modified rice tungro bacilliform virus (RTBV) vector in silencing Cynodon dactylon and Zoysia japonica phytoene desaturase ( PDS ) gene through agroinfiltration. The agroinfiltrated leaves of two Cynodon dactylon and two Zoysia japonica cultivars all showed white streaks typical for PDS gene silencing at 21 days post agroinfiltration. In Cynodon dactylon and Zoysia japonica plants displaying white streak leaf symptoms, PDS gene expression in leaves were all significantly lower than that of control and mock-infected plants. These results indicated that RTBV-VIGS system is efficient in Cynodon dactylon and Zoysia japonica . [ABSTRACT FROM AUTHOR]