cDNA cloning and molecular characterization of cherry green ring mottle virus

Complete genome sequence of a novel robigovirus infecting Mentha arvensis

The complete genomic sequence of a novel robigovirus, provisionally named "Mentha arvensis robigovirus 1" (MARV1), was determined by combining next-generation sequencing (NGS), reverse transcription polymerase chain reaction (RT-PCR), and rapid amplification of cDNA ends (RACE) PCR. The complete genomic sequence of this new virus is 7617 nucleotides in length, excluding the 3' poly(A) tail. The MARV1 genome encodes a putative replicase, "triple gene block" proteins, and a coat protein. Phylogenetic analysis demonstrated that MARV1 is a member of the genus Robigovirus, with closest relationships to African oil palm ringspot virus (AOPRV). Furthermore, MARV1-derived small interfering RNAs (siRNAs) showed typical patterns of plant-virus-derived siRNAs produced by the host antiviral RNA interference pathway. This is the first report of a plant virus of the genus Robigovirus in M. arvensis.

Systemic infection and symptom development of agro-inoculated cDNA clone of cherry rusty mottle-associated virus in sweet cherry (Prunus avium)

Cherry rusty mottle-associated virus (CRMaV), which belongs the genus Robigovirus of the family Betaflexiviridae, is strongly associated with cherry rusty mottle disease of sweet cherry, Prunus avium. Here, we report on the successful development of an Agrobacterium-based inoculation system for a cloned CRMaV cDNA construct. Agro-inoculation of virus-free cherry rootstock 'Krymsk6' [P. cerasus x (P. cerasus x P. maackii)] resulted in the development of chlorotic yellow mottle symptoms on systemic leaves beginning at 50 days post inoculation. The presence of CRMaV in 'Krymsk6' agro-inoculated plants was confirmed by RT-PCR and ELISA. Subsequently, CRMaV from agro-inoculated 'Krymsk6' was graft-transmissible onto virus-free sweet cherry rootstock P. avium 'Mazzard' as evidenced by the production of typical cherry rusty mottle symptoms beginning at 35 days post grafting, and further confirmed by western blotting and RT-PCR. These results showed conclusively that CRMaV is the causal agent of cherry rusty mottle disease in sweet cherry. The reverse genetic system presented in this study can be used as a tool to investigate the molecular biology of CRMaV and also a template for infectious clone development for other viruses in the genus Robigovirus.

Discovery and Survey of a New Mandarivirus Associated with Leaf Yellow Mottle Disease of Citrus in Pakistan

During biological indexing for viruses in citrus trees, in a collection of Symons sweet orange (SSO) (Citrus sinensis L. Osbeck) graft inoculated with bark tissues of citrus trees from the Punjab Province in Pakistan, several SSO trees exhibited leaf symptoms of vein yellowing and mottle. High-throughput sequencing by Illumina of RNA preparation depleted of ribosomal RNAs from one symptomatic tree, followed by BLAST analyses, allowed identification of a novel virus, tentatively named citrus yellow mottle-associated virus (CiYMaV). Genome features of CiYMaV are typical of members of the genus Mandarivirus (family Alphaflexiviridae). Virus particles with elongated flexuous shape and size resembling those of mandariviruses were observed by transmission electron microscopy. The proteins encoded by CiYMaV share high sequence identity, conserved motifs, and phylogenetic relationships with the corresponding proteins encoded by Indian citrus ringspot virus (ICRSV) and citrus yellow vein clearing virus (CYVCV), the two current members of the genus Mandarivirus. Although CYVCV is the virus most closely related to CiYMaV, the two viruses can be serologically and biologically discriminated from each other. A reverse-transcription PCR method designed to specifically detect CiYMaV revealed high prevalence (62%) of this virus in 120 citrus trees from the Punjab Province, Pakistan, where the novel virus was found mainly in mixed infection with CYVCV and citrus tristeza virus. However, a preliminary survey on samples from 200 citrus trees from the Yunnan Province, China failed to detect CiYMaV in this region, suggesting that the molecular, serological, and biological data provided here are timely and can help to prevent the spread of this virus in citrus-producing countries.

First identification and molecular characterization of a novel cherry robigovirus

A large contig with sequence similarities to members of the genus Robigovirus was identified by high-throughput sequencing analysis from a symptomless cherry accession. The complete genome sequence of this new virus is 8,384 nucleotides in length, excluding the 3' poly(A) tail. Its genome organization is very similar to those of four known robigoviruses, encoding a putative replicase, three 'triple gene block' proteins, a coat protein, and an unknown protein, 2a. Unlike the four cherry robigoviruses, the new virus does not contain a putative ORF5a. The full-length genome of the virus, which is provisionally named "cherry robigovirus 5" (CRV-5), is 52-57% identical to genome sequences of other robigoviruses. Phylogenetic analysis showed that CRV-5 and other robigoviruses group in a cluster, supporting its assignment to a new species in the genus Robigovirus.

A Virus in American Blackcurrant (Ribes americanum) with Distinct Genome Features Reshapes Classification in the Tymovirales

A novel virus with distinct genome features was discovered by high throughput sequencing in a symptomatic blackcurrant plant. The virus, tentatively named Ribes americanum virus A (RAVA), has distinct genome organization and molecular features bridging genera in the order Tymovirales. The genome consists of 7106 nucleotides excluding the poly(A) tail. Five open reading frames were identified, with the first encoding a putative viral replicase with methyl transferase (MTR), AlkB, helicase, and RNA dependent RNA polymerase (RdRp) domains. The genome organization downstream of the replicase resembles that of members of the order Tymovirales with an unconventional triple gene block (TGB) movement protein arrangement with none of the other four putative proteins exhibiting significant homology to viral proteins. Phylogenetic analysis using replicase conserved motifs loosely placed RAVA within the Betaflexiviridae. Data strongly suggest that RAVA is a novel virus that should be classified as a species in a new genus in the Betaflexiviridae or a new family within the order Tymovirales.

Genomic analyses of cherry rusty mottle group and cherry twisted leaf-associated viruses reveal a possible new genus within the family betaflexiviridae

It is demonstrated that closely related viruses within the family Betaflexiviridae are associated with a number of diseases that affect sweet cherry (Prunus avium) and other Prunus spp. Cherry rusty mottle-associated virus (CRMaV) is correlated with the appearance of cherry rusty mottle disease (CRMD), and Cherry twisted leaf-associated virus (CTLaV) is linked to cherry twisted leaf disease (CTLD) and apricot ringpox disease (ARPD). Comprehensive analysis of previously reported full genomic sequences plus those determined in this study representing isolates of CTLaV, CRMaV, Cherry green ring mottle virus, and Cherry necrotic rusty mottle virus revealed segregation of sequences into four clades corresponding to distinct virus species. High-throughput sequencing of RNA from representative source trees for CRMD, CTLD, and ARPD did not reveal additional unique virus sequences that might be associated with these diseases, thereby further substantiating the association of CRMaV and CTLaV with CRMD and CTLD or ARPD, respectively. Based on comparison of the nucleotide and amino acid sequence identity values, phylogenetic relationships with other triple-gene block-coding viruses within the family Betaflexiviridae, genome organization, and natural host range, a new genus (Robigovirus) is suggested.

Control of pome and stone fruit virus diseases

Many different systemic pathogens, including viruses, affect pome and stone fruits causing diseases with adverse effects in orchards worldwide. The significance of diseases caused by these pathogens on tree health and fruit shape and quality has resulted in the imposition of control measures both nationally and internationally. Control measures depend on the identification of diseases and their etiological agents. Diagnosis is the most important aspect of controlling fruit plant viruses. Early detection of viruses in fruit trees or in the propagative material is a prerequisite for their control and to guarantee a sustainable agriculture. Many quarantine programs are in place to reduce spread of viruses among countries during international exchange of germplasm. All these phytosanitary measures are overseen by governments based on agreements produced by international organizations. Also certification schemes applied to fruit trees allow the production of planting material of known variety and plant health status for local growers by controlling the propagation of pathogen-tested mother plants. They ensure to obtain propagative material not only free of "quarantine" organisms under the national legislation but also of important "nonquarantine" pathogens. The control of insect vectors plays an important role in the systemic diseases management, but it must be used together with other control measures as eradication of infected plants and use of certified propagation material. Apart from the control of the virus vector and the use of virus-free material, the development of virus-resistant cultivars appears to be the most effective approach to achieve control of plant viruses, especially for perennial crops that are more exposed to infection during their long life span. The use of resistant or tolerant cultivars and/or rootstocks could be potentially the most important aspect of virus disease management, especially in areas in which virus infections are endemic. The conventional breeding for virus-tolerant or resistant fruit tree cultivars using available germplasm is a long-term strategy, and the development and production of these cultivars may take decades, if successful. Genetic engineering allows the introduction of specific DNA sequences offering the opportunity to obtain existing fruit tree cultivars improved for the desired resistance trait. Unfortunately, genetic transformation of pome and stone fruits is still limited to few commercial genotypes. Research carried out and the new emerging biotechnological approaches to obtain fruit tree plants resistant or tolerant to viruses are discussed.

Analysis of the complete genome of a virus associated with twisted leaf disease of cherry reveals evidence of a close relationship to unassigned viruses in the family Betaflexiviridae

The genome of a virus associated with cherry twisted leaf disease (CTLaV, isolate ZH) was sequenced and consists of 8431 nucleotides, excluding a poly(A) tail at the 3' end. Genome analysis shows that CTLaV-ZH represents a new and distinct species and has a genome organization similar to those of unassigned viruses in the family Betaflexiviridae. The CTLaV-ZH genome has five open reading frames (ORFs), with putative ORFs within ORF2 and ORF5, identified as ORF2a and ORF5a, respectively. The AUG start codons of ORF2a and ORF5a are in contexts suitable for efficient translation, with appropriate stop codons in frame.

Viruses associated with rusty mottle and twisted leaf diseases of sweet cherry are distinct species

Virus RNA sequences related to those of the family Betaflexiviridae were amplified from trees affected with the following diseases: cherry twisted leaf, apricot ring pox, cherry necrotic rusty mottle, cherry rusty mottle, and cherry green ring mottle. Phylogenetic analysis of virus sequences obtained from these diseased trees from western North America, along with published sequences of Cherry green ring mottle virus (CGRMV) and Cherry necrotic rusty mottle virus (CNRMV), revealed four major clades. Segregation into these four populations correlated with distinct symptom expression on woody indicators, suggesting that each clade represents a distinct virus species within the family Betaflexiviridae. The viruses occupying each clade were designated clade I: Cherry twisted leaf associated virus, clade II: CNRMV, clade III: Cherry rusty mottle associated virus, and clade IV: CGRMV. Potential recombination events were predicted to occur within and between these viruses, the latter being strongly supported by incongruent phylogenies. Examination of frequency distribution data derived from pairwise sequence comparisons of coat protein coding sequences resulted in a proposal for alternative guidelines for species demarcation for this family of viruses.

A duplex, SYBR Green I-based RT-qPCR assay for the simultaneous detection of Apple chlorotic leaf spot virus and Cherry green ring mottle virus in peach

Background

Co-infections of Apple chlorotic leaf spot virus (ACLSV) and Cherry green ring mottle virus (CGRMV) in peach is common in China and have resulted in significant yield reductions. A reliable, sensitive and quantitive method is needed to detect and distinguish between ACLSV and CGRMV in peach.

Findings

We developed a sensitive and specific SYBR Green-I based RT-qPCR for the quantification of ACLSV and CGRMV in different peach tissues, and a duplex RT-qPCR system to detect ACLSV and CGRMV simultaneously. The RT-qPCR method was optimized using standard samples transcribed by the T7 Large Scale RNA Production System in vitro. The peach genes, RNA Polymerase subunit II (RPII) and Ubiquitin 10 (UBQ10), which were used as the internal controls for the quantification assay also showed good expression stability in this system. Single RT-qPCR assays showed that CGRMV in peach accumulates to a higher level than ACLSV. The detection limits of the duplex RT-qPCR assay were 10² and 10⁴ copies for ACLSV and CGRMV, respectively. The sensitivity of the duplex RT-qPCR was as high as RT-qPCR and higher than RT-PCR.

Conclusions

The SYBR Green-I RT-qPCR assay provided a sensitive, specific and reliable method for the detection and quantification of ACLSV and CGRMV in different peach tissues. The duplex RT-qPCR system provided a sensitive and specific method to detect and differentiate between ACLSV and CGRMV in a single sample. This RT-qPCR assay could be a useful tool for the routine diagnosis of these two viruses and for disease epidemiology studies in peach orchards.

Complete nucleotide sequence of a virus associated with rusty mottle disease of sweet cherry (Prunus avium)

Cherry rusty mottle is a disease of sweet cherries first described in 1940 in western North America. Because of the graft-transmissible nature of the disease, a viral nature of the disease was assumed. Here, the complete genomic nucleotide sequences of virus isolates from two trees expressing cherry rusty mottle disease symptoms are characterized; the virus is designated cherry rusty mottle associated virus (CRMaV). The biological and molecular characteristics of this virus in comparison to those of cherry necrotic rusty mottle virus (CNRMV) and cherry green ring mottle virus (CGRMV) are described. CRMaV was subsequently detected in additional sweet cherry trees expressing symptoms of cherry rusty mottle disease.

Identification and characterization of citrus yellow vein clearing virus, a putative new member of the genus Mandarivirus

Molecular features and genomic organization were determined for Citrus yellow vein clearing virus (CYVCV), the putative viral causal agent of yellow vein clearing disease of lemon trees, reported in Pakistan, India, and more recently in Turkey and China. CYVCV isolate Y1 from Adana, Turkey, was used for deep sequencing analysis of the virus-induced small RNA fractions and for mechanical and graft inoculation of herbaceous and citrus indicator plants. A polyclonal antiserum was developed from CYVCV-Y1 purified from Phaseolus vulgaris and used in western blot assays to characterize the coat protein of CYVCV-Y1 and determine its serological relationship with related viruses. Contigs assembled from the Illumina sequenced short reads were used to construct the whole genome of Citrus yellow vein clearing virus (CYVCV), consisting in a positive-sense RNA of 7,529 nucleotides and containing six predicted open reading frames. The CYVCV genome organization and size resembled that of flexiviruses, and search for sequence homologies revealed that Indian citrus ringspot virus (ICRSV) (Mandarivirus, Alphaflexiviridae) is the most closely related virus. However, CYVCV had an overall nucleotide sequence identity of ≈74% with ICRSV. Although the two viruses were similar with regard to genome organization, viral particles, and herbaceous host range, CYVCV caused different symptoms in citrus and was serologically distinct from ICRSV. Primer pairs were designed and used to detect the virus by conventional and quantitative reverse transcription-polymerase chain reaction on yellow vein clearing symptomatic field trees as well as graft- and mechanically inoculated host plants. Collectively, these data suggest that CYVCV is the causal agent of yellow vein clearing disease and represents a new species in the genus Mandarivirus.

Complete nucleotide sequences of two isolates of cherry green ring mottle virus from peach (Prunus persica) in China

Two complete nucleotide sequences of cherry green ring mottle virus (CGRMV) isolated from peach in Hebei (Hs10) and Fujian (F9) Provinces, China, were determined. Five open reading frames (ORFs) were found in the genomes of both isolates. The F9 and Hs10 isolates shared 82.2 % and 83.4-94.4 % nucleotide sequence identity, respectively, with two CGRMV isolates from cherry. Analysis of the nucleotide and amino acid sequences from the five ORFs of both isolates showed that Hs10 shares the greatest sequence identity with P1A (GenBank AJ291761) from cherry. Phylogenetic analysis indicated that CGRMV isolates from peach and cherry are closely related to members of the genus Foveavirus.

Complete nucleotide sequence of cherry virus A (CVA) infecting sweet cherry in India

Cherry virus A (CVA) is a graft-transmissible member of the genus Capillovirus that infects different stone fruits. Sweet cherry (Prunus avium L; family Rosaceae) is an important deciduous temperate fruit crop in the Western Himalayan region of India. In order to determine the health status of cherry plantations and the incidence of the virus in India, cherry orchards in the states of Jammu and Kashmir (J&K) and Himachal Pradesh (H.P.) were surveyed during the months of May and September 2009. The incidence of CVA was found to be 28 and 13% from J&K and H.P., respectively, by RT-PCR. In order to characterize the virus at the molecular level, the complete genome was amplified by RT-PCR using specific primers. The amplicon of about 7.4 kb was sequenced and was found to be 7,379 bp long, with sequence specificity to CVA. The genome organization was similar to that of isolates characterized earlier, coding for two ORFs, in which ORF 2 is nested in ORF1. The complete sequence was 81 and 84% similar to that of the type isolate at the nucleotide and amino acid level, respectively, with 5' and 3' UTRs of 54 and 299 nucleotides, respectively. This is the first report of the complete nucleotide sequence of cherry virus A infecting sweet cherry in India.

Characterization of a flowering cherry strain of Cherry necrotic rusty mottle virus

The host range and complete nucleotide sequences of two Cherry necrotic rusty mottle virus (CNRMV) isolates (FC4 and FC5) infecting flowering cherry accessions imported from Japan are described. Of the plants tested, cherry, peach, apricot and almond became infected, but only sweet cherry cv. 'Canindex', Nanking cherry and apricot cv. 'Tilton' showed a mild foliar mottle. The genomic sequences of CNRMV-FC4 and CNRMV-FC5 are 8,430 and 8,429 nt in length, excluding the 3' poly (A) tail. They contain seven open reading frames encoding for a putative virus replicase, "triple gene block" proteins, a coat protein and two proteins with unknown functions. The two CNRMV-FC isolates share 96% identity in the genomic sequences, and their genome organizations are virtually identical to that of a German CNRMV isolate (CNRMV-GER). However, they differ from CNRMV-GER by 14% in the overall nucleotide sequence and 2% (ORF2) to 30% (ORF5a) in the derived amino acid sequences of individual gene products.

An improved reverse transcription-polymerase chain reaction (RT-PCR) assay for the detection of two cherry flexiviruses in Prunus spp

A one-step reverse transcription-polymerase chain reaction (RT-PCR) procedure was developed to detect Cherry green ring mottle virus (CGRMV) and Cherry necrotic rusty mottle virus (CNRMV) in woody indicators and naturally infected Prunus spp. Viral RNA suitable for RT-PCR was obtained by a simple trapping method that did not require either extraction of double-stranded RNA (dsRNA) or total RNA, availability of virus antibodies, or purification of viral particles. Consensus primers, degenerate primers and virus-specific primers, whose designs were based on alignments of available cherry flexivirus sequences, were tested to amplify viral genomic fragments of six CGRMV isolates and one CNRMV isolate. RT-PCR allowed CGRMV detection in total RNA and viral RNA preparations equivalent to 400mug and 4mug of infected leaf tissue, respectively. CGRMV was detected in tender shoots, leaves, bark and root tips, and the strongest bands were obtained using young leaves. Detection was less consistent in summer when the temperature was elevated and plant tissues were old. A direct comparison of the RT-PCR and grafting assays indicated that the RT-PCR assay is sensitive, rapid and reliable. The method will improve the routine diagnosis of cherry flexiviruses in Prunus spp.

Polyvalent degenerate oligonucleotides reverse transcription-polymerase chain reaction: a polyvalent detection and characterization tool for trichoviruses, capilloviruses, and foveaviruses

ABSTRACT A polyvalent nested reverse transcription-polymerase chain reaction (RT-PCR) test using degenerate primers containing inosine (polyvalent degenerate oligonucleotides [PDO]) was developed for filamentous fruit tree viruses belonging to the genera Trichovirus, Capillovirus, and Foveavirus. The 362-bp product was amplified from nucleic acid extracts obtained from Prunus and Malus leaf samples. All the viruses targeted were detected, demonstrating the polyvalence of the test. The variability of a collection of Apple chlorotic leaf spot virus isolates was analyzed using the sequence of the PDO RT-PCR amplified cDNAs. The technique was also used to screen stone fruit materials infected with known agents or with virus-like graft-transmissible diseases of unknown etiology. The results obtained further validated the broad specificity of the assay, with positive amplification obtained for uncharacterized or partially characterized viruses associated with cherry and peach disorders. Sequencing the amplified PCR products either directly or after cloning allowed the identification of variants of known agents and the tentative identification of two new agents, a Trichovirus and a Foveavirus. In addition, sequence comparisons demonstrated that the sequence of the targeted region is phylogenetically informative and of predictive taxonomic value.

Biological and Molecular Characterization of a New Carlavirus Isolated from an Aconitum sp

ABSTRACT A new virus was isolated from symptomless Aconitum napellus plants. The virus, for which the name Aconitum latent virus (AcLV) is proposed, has flexuous particles 640 nm in length. The experimental host range was limited to Nicotiana clevelandii. Electron microscopy studies of ultrathin sections of infected A. napellus tissues revealed the presence of elongated virus particles. No inclusion bodies characteristic of potyvirus infection were observed. AcLV was purified from naturally infected A. napellus by cesium chloride step gradient centrifugation. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis of dissociated purified virus preparations, a major protein component with a molecular mass of 35 kDa was observed. Diagnostic antibodies that could specifically bind to virus particles were produced. The 5' terminus (620 nucleotides) of the viral RNA was cloned and sequenced. It comprised 71 nucleotides from the untranslated 5' terminus and 549 nucleotides of an open reading frame encoding 183 amino acids. Comparison of the predicted amino acid sequence with those of other plant viruses revealed 40 to 60% identity with several carlaviruses. Based on particle morphology, absence of inclusion bodies in ultrathin sections, the relative molecular weight of the coat protein, the nucleotide sequence, and predicted amino acid homology, it is suggested that this virus belongs to the carlavirus group.

Nucleotide sequence and rt-PCR detection of a virus associated with grapevine rupestris stem-pitting disease

ABSTRACT Grapevine rupestris stem pitting (RSP) is a graft-transmissible disease of unknown etiology. We have characterized a virus associated with this disease. The entire genomic sequence (GenBank accession number AF026278) consisted of 8,725 nucleotides excluding a poly(A) tail. Six open reading frames (ORF) were found. ORF1 potentially encodes a polypeptide with a methyltransferase domain, a papain-like proteinase domain, a helicase domain, and a RNA-dependent RNA polymerase domain; ORF2, ORF3, and ORF4 compose a triple-gene block; ORF5 encodes a coat protein; and ORF6 is located near the 3' end with unknown function. Sequence analysis indicated that the virus is most similar to apple stem-pitting virus and may be allied with the carla- and potexviruses and grouped with other viruses that infect woody hosts. A specific reverse-transcription polymerase chain reaction (RT-PCR)-based detection method was developed. Among 62 grapevine sources known to be infected with rupestris stem-pitting disease, 60 sources tested positive by RT-PCR. Among 43 healthy vines tested, all were negative. The name grapevine rupestris stem-pitting-associated virus is proposed.