The family contains viruses infecting plants which share a distinct lineage of alphavirus-like replication proteins.
Virions are flexuous filaments, usually 12–13 nm in diameter (range 10–15 nm) and from 600 to over 1000 nm in length, depending on the genus. They have helical symmetry with a pitch of about 3.4 nm (range 3.3–3.7 nm) and in some genera there is clearly visible cross-banding.
Virions sediment as single (or occasionally two very close) bands with an S20,w of 92–176S, depending on the genus.
Virions contain a single molecule of linear ssRNA of about 5.9–9.0 kb which is 5–6% by weight of the virion. The RNA is capped (or probably capped) at the 5’ terminus with m7G and has a polyadenylated tract at the 3’ terminus. In the genus Carlavirus some viruses have two subgenomic RNAs (sgRNAs) of 2.1–3.3 kb and 1.3–1.6 kb, which are possibly encapsidated in shorter particles.
The viral capsid of all members is composed of a single polypeptide ranging in size from 18 to 44 kDa.
The number of genes is between three and six depending upon the genus (Figure 1) but, in all species, the ORF1-encoded product, which follows a short 5’-UTR sequence, has homologies with polymerase proteins of the “alphavirus-like” supergroup of RNA viruses. This protein (190–250 kDa) contains the conserved domains for methyltransferase (Mtr), helicase (Hel) and RNA-dependent RNA polymerase (RdRp) activity. Most members also have AlkB and papain-like protease (P-Pro) domains between the Mtr and Hel. Smaller ORFs encode the proteins involved in cell-to-cell movement, either a single MP of the “30K” superfamily (Capillovirus, Citrivirus, Trichovirus, Vitivirus) or a “triple gene block” (TGB) (remaining genera and viruses). These are usually located following (3’-proximal to) the polymerase but in capillovirus genomes the MP ORF2 is nested within the ORF1 and in vitiviruses an extra ORF is present between the polymerase and MP genes. The CP gene always follows the MP(s) and in some genera (Carlavirus, Vitivirus and some trichoviruses) a final ORF encodes a protein with a zinc binding finger motif and the ability to bind nucleic acids. In vitiviruses, this small protein has been shown to have RNA silencing suppressor activity. ORFs downstream of the polymerase are translated from 3’-terminal sgRNAs that can often be found in infected tissue. In some viruses, notably in the genera Citrivirus, Vitivirus and Trichovirus, nested sets of 5’-terminal sgRNAs and their associated dsRNAs can also be detected. Replication is (or is presumed to be) cytoplasmic and the product of ORF1 is the only virus-encoded protein known to be involved.
Virions are highly immunogenic in members of the genus Carlavirus but those of other genera are only moderate to poor antigens. Within (but not usually between) genera, some viruses are serologically related.
Members have been reported from a diverse range of plant species but the host range of individual members is usually limited. With the exception of most members of the genus Carlavirus, natural infections are mostly or exclusively of woody hosts. Many of the viruses have relatively mild effects on their host. All species can be transmitted by mechanical inoculation, although some with difficulty. Many of the viruses have no known invertebrate or fungus vectors; however some trichoviruses are known to be mite-borne, most carlaviruses are transmitted naturally by aphids in the non-persistent manner and a range of vectors (pseudococcid mealybugs, scale insects and aphids) have been reported for different vitiviruses. Aggregates of virus particles accumulate in the cytoplasm. Many carlaviruses induce the formation of ovoid or irregularly shaped inclusions but otherwise there are usually no specific cytopathic structures.
Genera are distinguished by various features of genome organization and the natural mode of transmission. These are summarized in Table 1. Throughout the family, isolates of different species should have less than about 72% nt identity (or 80% aa identity) between their respective CP or polymerase genes. Viruses from different genera usually have less than about 45% nt identity in these genes.
Table 1 Distinguishing properties of genera in the family Betaflexiviridae
Virion length (nm)
3 or 4
a Rep, Replication protein size (kDa).
b MP, Movement protein either of the “30K” superfamily or a triple gene block (TGB).
c CP, Coat protein size (kDa).
Type species Apple stem grooving virus
Capilloviruses have a distinctive genomic organization, with two ORFs encoding a large replication-associated protein fused with the coat protein and (as a nested ORF) a putative movement protein. The MP and CP are expressed from subgenomic RNAs. No vectors are known. Virions have prominent cross-banding.
Virions are flexuous filaments, 640–700×12 nm, constructed from helically arranged protein subunits in a primary helix with a pitch of 3.4 nm and between 9 and 10 subunits per turn with prominent cross-banding (see Figure 1 above).
The S20,w of particles is about 112S, isoelectric point is about pH 4.3 at ionic strength 0.1 M, and electrophoretic mobility is 10.3 and 6.5×10−5 cm−2 sec−1 volt−1, at pH 7.0 and 6.0 respectively (ionic strength 0.1 M; data for apple stem grooving virus).
Virions contain linear positive sense ssRNA, 6.5–7.4 kb in size, constituting about 5%, by weight, of virions. The RNA is polyadenylated at its 3’ end. Isolates of the species Apple stem grooving virus from different hosts show wide variations in the sequence of a 284 aa region of ORF1-encoded protein, between the polymerase and CP domains.
Virions are composed of a single 24–27 kDa protein.
The genomic RNA of all sequenced viruses has the same organization, and two ORFs (Figure 2). ORF1 encodes a 240–266 kDa protein followed by a UTR of 140–300 nt upstream of the 3’-poly(A) tail. ORF2 is nested within ORF1 near its 3’ end, and encodes a 36–52 kDa protein. Although the CP cistron is located in the C-terminal end of ORF1, and ORF2 is nested within ORF1, the strategy of expression of both CP and putative MP may be based on sgRNA production, as suggested by the analysis of dsRNA patterns from infected tissues. dsRNAs of the type member consist of five major bands with sizes of approximately 6.5, 5.5, 4.5, 2.0 and 1.0 kbp. The 6.5 kbp species probably represents the double stranded form of the full-length genome, and the 2.0 and the 1.0 kbp species may be the double-stranded forms of sgRNAs that code for the putative MP and the CP, respectively. Replication is likely to occur in the cytoplasm, in which virus particles accumulate in discrete bundles.
Virions are moderately antigenic. There are no serological relationships between species.
Apple stem grooving virus (ASGV) is pathogenic to pome fruits and citrus and induces stock/scion incompatibility, i.e. top-working disease of apple and bud union crease syndrome of citrus. It also infects lily. Cherry virus A (CVA) is frequently found in sweet and sour cherry (and less frequently in other Prunus hosts) but no disease has been associated with it.
No vectors are known. ASGV was transmitted through seed to progeny seedlings of Chenopodium quinoa, and lily. ASGV, CVA, and Nandina stem pitting virus (NSPV) are transmitted by grafting. NSPV has not been transmitted by sap inoculation, but by slashing stems with a partially purified virus preparation.
Geographical distribution ranges from wide to restricted according to the virus. ASGV has been recorded from most areas where apples are grown, and is widespread in citrus in China, Japan, United States, Australia and South Africa. CVA is widespread and probably occurs worldwide in cherry hosts. NSPV is found only in the United States.
No distinct cytological alterations have been observed in infected cells. Virus particles occur in bundles in mesophyll and phloem parenchyma cells, but not in the epidermis and sieve elements.
The criteria demarcating species in the genus are:
Apple stem grooving virus
Apple stem grooving virus-P-209
Citrus tatter leaf virus-lily
Cherry virus A
Cherry virus A-Germany
Species names are in italic script; names of isolates and strains are in roman script. Sequence accessions [ ] and assigned abbreviations ( ) are also listed.
Nandina stem pitting virus
Type species Carnation latent virus
Carlaviruses have six ORFs, including a TGB, and are insect-transmitted.
Virions are slightly flexuous filaments, 610–700 nm in length and 12–15 nm in diameter (Figure 3). They have helical symmetry with a pitch of about 3.4 nm.
Virion Mr is about 60×106, with a nucleic acid content of about 6%. Virion S20,w is 147–176S, and the buoyant density in CsCl solutions is 1.3 g cm−3.
Virions contain a single molecule of linear ssRNA that has a size range of 7.4–7.7 kb when estimated by agarose gel analysis, although full-length sequence analysis suggests that genome sizes are in the 8.3–8.7 kb range. Some species also have two sgRNAs of 2.1–3.3 kb and 1.3–1.6 kb, which are possibly encapsidated in shorter particles. The genomic RNAs have a 3’-poly(A) tract and a 5’-cap.
There are typically six ORFs with short UTRs at the 5’ and 3’ termini. In potato virus M (Figure 4), ORF1 encodes a polypeptide of 223 kDa that is the viral replicase; ORFs 2, 3 and 4 form the triple gene block and encode polypeptides of 25, 12 and 7 kDa which facilitate virus movement. ORF5 encodes the 34 kDa CP and overlaps ORF6, which encodes a cysteine-rich protein of 11–16 kDa. The function of the 11–16 kDa polypeptide has yet to be determined, but its ability to bind nucleic acid indicates that it may facilitate aphid transmission or be involved in host gene transcription/gene silencing and/or viral RNA replication.
Only ORF1 is translated from the full length genomic RNA. With blueberry scorch virus and probably other carlaviruses the product of ORF1 is proteolytically processed by a papain-like proteinase activity, with about 30–40 kDa being removed. The 3’-terminal ORFs appear to be translated from two sgRNAs that can be found in infected tissue, and, for some viruses, can be detected in purified virus preparations. The 5’-untranslated leader sequence of the genomic RNA and the sgRNA for the CP of potato virus S (PVS) have both been shown to act as efficient enhancers of translation.
Carlavirus virions are good immunogens. Some species are serologically interrelated, but others are apparently distinct.
Individual viruses have restricted natural host ranges, but some can infect a wide range of experimental hosts.
Most species are transmitted naturally by aphids in the non-persistent manner; cowpea mild mottle virus (CPMMV) is transmitted by whiteflies (Bemisia tabaci), pea streak virus, red clover vein mosaic virus and CPMMV are seedborne in their leguminous hosts. All are mechanically transmissible; some (e.g. carnation latent virus and PVS) are sufficiently infectious to be so transmitted this way in the field.
The geographical distribution of many species is restricted, but those infecting vegetatively-propagated crops are usually widely distributed, presumably due to inadvertent dissemination in vegetative propagules. Most species commonly occur in temperate climates, but CPMMV is restricted to tropical and sub-tropical regions.
Virions of aphid-borne species are scattered throughout the cytoplasm or occur in membrane-associated bundle-like or plate-like aggregates. Many species also induce the formation of ovoid or irregularly shaped inclusions that appear in the light microscope as vacuolate bodies; these consist of aggregates of virus particles, mitochondria, endoplasmic reticulum and lipid globules. The particles of CPMMV, the whitefly-transmitted carlavirus, also occur in aggregates in cytoplasm; those of most, but not all, strains of CPMMV form brush-like inclusions.
Each distinct species usually has a specific natural host range. Distinct species do not cross-protect in infected common host plant species. Distinct species are readily differentiated by serological procedures; strains of individual species are often distinguishable in reactions with polyclonal antisera, but more readily so with monoclonal antibodies. Distinct species have less than about 72% nt identity (or 80% aa identity) between their CP or polymerase genes.
Aconitum latent virus
Aconitum latent virus-Japan:D
American hop latent virus
American hop latent virus-USA:Washington State
Blueberry scorch virus
Blueberry scorch virus-NJ-2
Cactus virus 2
Cactus virus 2-Germany
Caper latent virus
Caper latent virus-Italy
Carnation latent virus
Carnation latent virus-United Kingdom
Chrysanthemum virus B
Chrysanthemum virus B-Japan:Showa
Cole latent virus
Cole latent virus-Brazil
Coleus vein necrosis virus
Coleus vein necrosis virus-USA
Cowpea mild mottle virus
Cowpea mild mottle virus-M
Dandelion latent virus
Dandelion latent virus-Canada:British Colombia
Daphne virus S
Daphne virus S-type strain: K
Elderberry symptomless virus
Elderberry symptomless virus-United Kingdom
Garlic common latent virus
Garlic common latent virus-Germany
Helenium virus S
Helenium virus S-Germany
Helleborus net necrosis virus
Helleborus net necrosis virus-G5
Honeysuckle latent virus
Honeysuckle latent virus-United Kingdom
Hop latent virus
Hop latent virus-Japan
Hop mosaic virus
Hop mosaic virus-Australia
Hydrangea latent virus
Hydrangea latent virus-USA
Kalanchoë latent virus
Kalanchoë latent virus-PV-0290B
Ligustrum necrotic ringspot virus
Ligustrum necrotic ringspot virus-USA
Lilac mottle virus
Lilac mottle virus-USA
Lily symptomless virus
Lily symptomless virus-South Korea
Melon yellowing-associated virus
Melon yellowing-associated virus-Bessa
Mulberry latent virus
Mulberry latent virus-Japan
Muskmelon vein necrosis virus
Muskmelon vein necrosis virus-USA:California
Narcissus common latent virus
Narcissus common latent virus-Zhangzhou
Narcissus symptomless virus
Narcissus symptomless virus-Hangzhou
Nerine latent virus
(Hippeastrum latent virus)
Nerine latent virus-Taiwan
Passiflora latent virus
Passiflora latent virus-Israel
Pea streak virus
Pea streak virus-ATCCPV-87
Poplar mosaic virus
Poplar mosaic virus-PV-0341
Potato latent virus
Potato latent virus-Canada
Potato virus M
Potato virus M-Russian wild type
Potato virus P
Potato virus P-Brazil
Potato rough dwarf virus
Potato virus S
Potato virus S-Leona
Red clover vein mosaic virus
Red clover vein mosaic virus-Washington
Shallot latent virus
Shallot latent virus-YH1
Sint-Jan’s onion latent virus
Sint-Jan’s onion latent virus-Netherlands
Strawberry pseudo mild yellow edge virus
Strawberry pseudo mild yellow edge virus-USA
Sweet potato chlorotic fleck virus
Sweet potato chlorotic fleck virus-Uganda
Verbena latent virus
Verbena latent virus-Israel
Species names are in italic script; names of isolates are in roman script; names of synonyms are in roman script and parentheses. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.
* Sequences do not comprise the complete genome.
Arracacha latent virus
Artichoke latent virus M
Artichoke latent virus S
Butterbur mosaic virus
Cardamine latent virus
Carrot virus S
Helleborus mosaic virus
Hydrangea chlorotic mottle virus
Phlox virus B
Phlox virus M
Phlox virus S
Sedum latent virus
Type species Citrus leaf blotch virus
This genus consists of a single species. There are three ORFs, similar to trichoviruses, but it is distinct from them in phylogenetic analyses, has longer virions and a much larger coat protein that more closely resembles those of foveaviruses.
Virions are slightly flexuous filaments, 960 nm in length and 12–15 nm in diameter (Figure 5).
Virions contain a single molecule of positive sense ssRNA, about 8.7 kb long. There is a methylated cap at the 5’ terminus and a polyadenylated 3’ terminus.
The viral capsid is composed of a single polypeptide of about 41 kDa.
The genome contains three ORFs (Figure 6). ORFs 2 and 3 are separated by a short intergenic region and ORFs 1 and 2 overlap by 1 nt. ORF1 is the replication protein and is probably directly expressed from genomic RNA. It is assumed that the two smaller downstream ORFs, which code respectively for the putative “30K” MP and CP, are expressed via sgRNAs.
The virus causes abnormal bud union and leaf blotching in various citrus varieties. Citrus is the only known natural host and mechanical transmission to a range of herbaceous hosts has been unsuccessful.
The virus is transmitted to citrus by grafting. There is no known natural vector.
The virus has been reported from citrus germplasm worldwide.
Citrus leaf blotch virus
(Dweet mottle virus)
Citrus leaf blotch virus-SRA-153
Type species Apple stem pitting virus
Foveaviruses are distinct in having five ORFs and larger CPs than most other members of the family.
Virions are flexuous filaments, about 800 to over 1000 nm in length and 12–15 nm in diameter with helical symmetry exhibiting a surface pattern with cross-banding and longitudinal lines (Figure 7). Particles of some viruses, including apple stem pitting virus (ASPV), show a tendency for end-to-end aggregation.
ASPV virions sediment as two or three bands in sucrose density gradients but yield a single band at equilibrium in Omnipaque 350 density gradients. They resist moderately high temperatures (thermal inactivation is around 60 °C) but not organic solvents, and are unstable in cesium chloride and sulfate.
Virions contain a single molecule of positive sense ssRNA, polyadenylated at the 3’ terminus.
The viral capsid of all species is composed of a single polypeptide with a size ranging from 28 kDa (grapevine rupestris stem pitting-associated virus, GRSPaV) to 44 kDa (ASPV and apricot latent virus, ApLV).
The genomes of all fully sequenced members contain five ORFs (Figure 8). The 5’ region initiates with a UTR of 33–72 nt, ORF1 codes for the replication-related protein, ORF2, ORF3 and ORF4 constitute the TGB and ORF5 is the CP cistron. A non-coding sequence of 176–312 nt followed by a poly(A) tail terminate the genome. ASPV virions accumulate in the cytoplasm, where multiplication is likely to occur following a strategy comparable to that of other viruses in the family, based on direct expression of the 5’-proximal ORF, and expression of downstream ORFs from sgRNAs. Multiple dsRNAs are found in infected hosts.
Antisera to ASPV that can be used for serological detection tests have been raised from purified virions or chimeric fusion CPs expressed in E. coli. ASPV and ApLV are serologically related, but there are no recognized serological relationships among other members of the genus.
The natural host range of individual species is restricted to a single (GRSPaV) or a few hosts (ASPV, ApLV). ASPV infects primarily pome fruits, causing diseases of apple (topworking disease) when grafted on susceptible rootstocks, of pear (vein yellows and necrotic spot) and quince. ApLV is the putative agent of peach asteroid spot and peach sooty ringspot diseases. GRSPaV is a pathogen of grapevine. Experimental host ranges are also restricted.
No vector is known for any of the viruses. ASPV is transmitted by grafting and persists in the host propagative material. ASPV is mechanically transmissible, with some difficulty, to Nicotiana occidentalis and its subspecies obliqua.
All members have a wide geographical distribution.
ASPV elicits a severe derangement of the cytology of infected cells but no specific cytopathic structures or inclusion bodies. Virus particles accumulate in bundles in the cytoplasm.
Apple stem pitting virus
Apple stem pitting virus-PA66
Apricot latent virus
Apricot latent virus-Caserta12
Grapevine rupestris stem pitting-associated virus
Grapevine rupestris stem pitting-associated virus-USA
Peach chlorotic mottle virus
Peach chlorotic mottle virus-Agua-4N6
Species names are in italic script; names of isolates are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.
Asian prunus virus 1
Asian prunus virus 2
Asian prunus virus 3
Type species: Potato virus T
Potato virus T
Potato virus T-Peru
Type species Apple chlorotic leaf spot virus
Trichoviruses have three (or sometimes four) ORFs including a movement protein of the “30K” superfamily.
Virions are very flexuous filaments, 640–890×10–12 nm in size, helically constructed with a pitch of 3.3–3.5 nm, and about 10 subunits per turn of the helix. Virions may show cross banding, criss-cross or rope-like features according to the negative contrast material used (Figure 9).
Virions sediment as single or as two very close bands with an S20,w of about 100S. Apple chlorotic leaf spot virus (ACLSV) virions are sensitive to ribonucleases. Virions of all viruses in the genus resist moderately high temperatures (thermal inactivation is around 55–60 °C) and are moderately resistant to organic solvents.
Virions contain a single molecule of linear, positive sense, ssRNA about 7.5– 8.0 kb in size, with a polyadenylated 3’ terminus, accounting for about 5% of the particle weight. Indirect evidence suggests that the genome RNA of ACLSV is capped at its 5’-end with m7G. An infectious cDNA clone of ACLSV has been produced. ACLSV isolates show a high variability in their nt sequence with an overall identity between 76 and 82%. The CP is the most conserved protein (87–93% identity), whilst the putative MP is the most divergent (77–85% identity).
Virions of all members are composed of a single 20.5–27 kDa polypeptide.
The genomes of ACLSV and grapevine berry inner necrosis virus (GINV) contain three slightly overlapping ORFs while other members and possible members of the genus have an additional ORF at the 3’ terminus (Figure 10). The large 5’ ORF of ACLSV is directly expressed from genomic RNA, whereas the two smaller downstream ORFs that code, respectively, for the MP and CP, are expressed via sgRNAs. The fourth ORF (where present) has homologies to the vitivirus nucleic acid binding proteins. ACLSV-infected tissues contain six dsRNA species of approximately 7.5, 6.4, 5.4, 2.2, 1.1 and 1.0 kbp. The 7.5 kbp species represents the double-stranded form of the full-length genome, whereas the 2.2 and the 1.1 kbp species are the double-stranded forms of sgRNAs coding for the MP and the CP, respectively. The most abundant dsRNA species, the function of which are unknown, are 5’ co-terminal with genomic RNA, and have sizes of 6.4 and 5.4 kbp, respectively. Replication is presumed to be cytoplasmic and to involve the translation product of ORF1. The MP of ACLSV is a suppressor of silencing that interferes with systemic movement of the silencing signal.
Virions are moderate to poor antigens. Cherry mottle leaf virus (CMLV) and peach mosaic virus (PcMV) are serologically related to one another but not to the other members of the genus.
The natural host range of individual species is relatively narrow (ACLSV, PcMV), or restricted to a single host (GINV, CMLV). The experimental host range is somewhat wider, but still limited to a few herbaceous species. In the natural hosts, infections induce few or no symptoms (ACLSV in certain hosts), or mottling, rings, line patterns and fruit injuries (i.e. pseudosharka) (ACLSV), mottling with stunting and internal necrosis of shoots and berries (GINV), mottling and severe distortion of the leaves (CMLV), mottling and deformation of leaves and fruits and color break in the petals (PcMV).
The viruses are readily transmitted by mechanical inoculation, by grafting (ACLSV, GINV, CMLV, PcMV) and through propagating material. GINV is transmitted by the grape erineum mite Colomerus vitis, CMLV by the scale mite Eriophyes inequalis, and PcMV by the peach bud mite Eriophyes insidiosus.
Geographical distribution varies from wide to restricted, according to the virus. ACLSV is ubiquitous, whereas GINV is reported only from Japan, and CMLV and PcMV from North America.
Infected cells are damaged by ACLSV to varying extents. Virions are found in phloem and parenchyma cells of leaves and roots and accumulate in the cytoplasm, sometimes in the nucleus, in bundles or paracrystalline aggregates. No inclusion bodies are formed.
Apple chlorotic leaf spot virus
Apple chlorotic leaf spot virus-P863
Apricot pseudo-chlorotic leaf spot virus
Apricot pseudo-chlorotic leaf spot virus-Sus2
Cherry mottle leaf virus
Cherry mottle leaf virus-SA1162-21
Grapevine berry inner necrosis virus
Grapevine berry inner necrosis virus-Japan
Peach mosaic virus
Peach mosaic virus-2022-01 (CA-1)
Fig latent virus 1
Phlomis mottle virus
Type species Grapevine virus A
Vitiviruses have a distinctive genome organization with five ORFs, including a 20K ORF between the polymerase and the movement protein of the “30K” superfamily. Natural transmission is by pseudococcid mealybugs, soft scale insects and aphids.
Virions are flexuous filaments 725–825×12 nm in size, showing distinct cross-banding, helically constructed with a pitch of 3.3–3.5 nm and about 10 subunits per turn of the helix (Figure 11).
Virions sediment as a single or two very close bands in sucrose or Cs2SO4 gradients, with an S20,w of about 92S. Virions of Heracleum latent virus (HLV) are sensitive to ribonucleases. Virions of all members of the genus resist moderately high temperatures (thermal inactivation is around 60 °C) and are moderately resistant to organic solvents.
Virions contain a single molecule of positive sense ssRNA, about 7.6 kb in size, capped at the 5’ terminus with m7G and polyadenylated at the 3’ terminus. The RNA accounts for about 5% of the particle weight. Infectious cDNA clones have been produced for grapevine viruses A and B (GVA and GVB).
The CPs are composed of a single 18–21.5 kDa polypeptide.
The genomes contain five slightly overlapping ORFs (Figure 12). The 5’ regions of grapevine viruses A and B initiate with an A/T-rich (60–68%) UTR of 47–86 nt. ORF1 is the replication-related protein. ORF2 is a 19–20 kDa polypeptide of unknown function with no significant sequence homology to known proteins, which, in GVB infections, does not accumulate in phase with MPs. ORF3 (31–36.5 kDa) is the movement protein and ORF4 is the CP. The final ORF is a 10–14 kDa polypeptide with weak homologies to proteins with RNA-binding properties and which has been shown (in GVA) to have RNA silencing suppressor activity.
The strategy of expression is based on sgRNA production, as suggested by the analysis of dsRNA patterns from infected tissues. The four dsRNAs have sizes of 7.6, 6.48, 5.68 and 5.1 kbp for GVA and GVD, and 7.6, 6.25, 5.03 and 1.97 kbp for GVB. In GVA there are nested sets of 5’-terminal sgRNAs 5.1, 5.5 and 6.0 kb in size and of 3’-terminal sgRNAs 1.0, 1.8 and 2.2 kb that serve for the expression of all ORFs, except for ORF5, which may be expressed via a bi- or polycistronic mRNA. The generation of these 5’- and 3’-terminal sgRNAs appears to be controlled by internal cis-acting elements. Replication occurs in the cytoplasm, possibly in association with membranous vesicles.
Virions are moderate or poor antigens. Most species are very distantly serologically related. Monoclonal antibodies to GVA, GVB and GVD and recombinant protein antibodies to the putative MP of GVA have been produced. The relationship between GVA, GVB and GVD is due to a few common internal antigenic determinants (cryptotopes). GVA particles carry a highly structured epitope centered in a common peptide region of the CP sequence.
The natural host range of individual species is restricted to a single host. Infections induce either no symptoms (HLV and mint virus 2 (MV-2)) or severe diseases characterized by pitting and grooving of the wood (GVA, GVB and GVD). The experimental host range varies from wide (HLV) to restricted (GVA, GVB, GVD and GVE).
All species except for MV-2 are transmitted by mechanical inoculation, those infecting grapevines with greater difficulty. Transmission by grafting and dispersal through propagating material is common with grapevine-infecting species. GVA and GVB are transmitted in a semi-persistent manner by different species of pseudococcid mealybugs of the genera Pseudococcus and Planococcus. GVA is also transmitted by the scale insect Neopulvinaria innumerabilis. HLV and MV-2 are transmitted semi-persistently by aphids, in association with a helper virus.
Geographical distribution varies from very wide (GVA, GVB, GVD) to restricted (HLV).
Infected cells are damaged to a varying extent. All species investigated elicit the formation of vesicular evaginations of the tonoplast containing finely fibrillar material, possibly representing replicative forms of viral RNA. Virions of grapevine-infecting species are strictly phloem-limited, but in herbaceous hosts they also invade the parenchyma. Virus particles accumulate in the cytoplasm in bundles or paracrystalline aggregates.
Grapevine virus A
Grapevine virus A-Is 151
Grapevine virus B
Grapevine virus B-Italy
Grapevine virus D
Grapevine virus D-Italy
Grapevine virus E
Grapevine virus E-Japan:TvAQ7
Heracleum latent virus
Heracleum latent virus-Scottish: Murant
Mint virus 2
Mint virus 2-USA
African oil palm ringspot virus
African oil palm ringspot virus-Colombia
Banana mild mosaic virus
Banana mild mosaic virus-Australia
Cherry green ring mottle virus
Cherry green ring mottle virus-USA
Cherry necrotic rusty mottle virus
Cherry necrotic rusty mottle virus-Germany
Sugarcane striate mosaic-associated virus
Sugarcane striate mosaic-associated virus-Australia
Banana virus X
White ash mosaic virus
In a phylogenetic analysis of the replication protein, most genera fall on well-supported branches (Figure 13, p. 938). The family falls into two broad parts that correspond with the types of movement protein. Carlavirus and Foveavirus with a number of unassigned species that have a TGB form one branch, while the remaining genera and viruses (which all have a “30K”-type movement protein) also cluster together. Of the unassigned species, Potato virus T is expected to become the type member of a new genus (proposed Tepovirus). The remaining unassigned species resemble foveaviruses in their genome organization but do not form a monophyletic group.
The polymerase proteins are members of the “alphavirus-like” supergroup of RNA viruses and are most closely related to those of the other families in the order, namely Alphaflexiviridae, Gammaflexiviridae and Tymoviridae. There are also similarities between the TGB-containing genera and members of the family Alphaflexviridae in the 3’ end of the genome (Figure 14, p. 939). The TGB proteins are also more distantly related to those of rod-shaped viruses in the family Virgaviridae (genera Hordeivirus, Pecluvirus and Pomovirus) (Figure 15a, p. 940). The “30K” movement proteins are related to those in the family Virgaviridae (genera Furovirus, Tobamovirus and Tobravirus) (Figure 15b, p. 940).
Capillo: from Latin capillus, “a hair”.
Carla: from Carnation latent virus.
Citri: from Citrus leaf blotch virus.
Flexi: from Latin flexus, “bent”.
Fovea: from Latin fovea, “pit” or “hole”, a type of symptom induced by the type species.
Tricho: from Greek thrix, “hair”.
Viti: from Vitis, generic name of the grapevine, Vitis vinifera, the host of the type species.
Adams et al., 2004 M.J. Adams, J.F. Antoniw, M. Bar-Joseph, A.A. Brunt, T. Candresse, G.D. Foster, G.P. Martelli, R.G. Milne, S.K. Zavriev, C.M. Fauquet, The new plant virus family Flexiviridae and assessment of molecular criteria for species demarcation. Arch. Virol. 149 (2004) 1045–1060.
Bratlie and Drabløs, 2005 M.S. Bratlie, F. Drabløs, Bioinformatic mapping of AlkB homology domains in viruses. BMC Genomics. 6 (2005) 1–15.
Martelli et al., 2007 G. Martelli, M.J. Adams, J.F. Kreuze, V.V. Dolja, Family Flexiviridae: a case study in virion and genome plasticity. Annu. Rev. Phytopathol. 45 (2007) 73–100.
Vives et al., 2001 M.C. Vives, L. Galipienso, L. Navarro, P. Moreno, J. Guerri, The nucleotide sequence and genomic organization of citrus leaf blotch virus: candidate type species for a new virus genus. Virology. 287 (2001) 225–233.
International Council for the Study of Virus and Virus-like Diseases of the Grapevine: http://www.icvg.ch.
Adams, M.J., Candresse, T., Hammond, J., Kreuze, J.F., Martelli, G.P., Namba, S., Pearson, M.N., Ryu, K.H., Saldarelli, P. and Yoshikawa, N.