The family Potyviridae consists of plant viruses with a single stranded, positive sense RNA genome and flexuous, filamentous particles. Genomes have a VPg covalently linked to the 5′ end and the 3′ terminus is polyadenylated. Genomes encode a large polyprotein that is self-cleaved into a set of functional proteins. Gene order and protein sequences are conserved throughout the family.
Virions are flexuous filaments with no envelope and are 11–15 nm in diameter, with a helical pitch of about 3.4 nm (Figure 1). Particle lengths of members of some of the six genera differ. Members of the genera Potyvirus, Ipomovirus, Macluravirus, Rymovirus, Tritimovirus, Brambyvirus and the unassigned viruses are monopartite with particle modal lengths of 650–900 nm; members of the genus Bymovirus are bipartite with particles of two modal lengths of 250–300 and 500–600 nm.
Virions of viruses in the genera Potyvirus and Rymovirus have a density in CsCl of about 1.31 g cm−3 and S20,w of 137–160S. Those of the genus Bymovirus have a density in CsCl of about 1.29 g cm−3.
Viruses in all genera except Bymovirus have a single molecule of positive sense, ssRNA, 9.3–10.8 kb in size. Virions are infectious. A VPg of about 24 kDa is covalently linked to the 5′-terminal nt. A polyadenylate tract (20 to 160 adenosines) is present at the 3′ terminus. Bymoviruses have two positive sense, ssRNA molecules; RNA-1 is 7.3–7.6 kb in size and RNA-2 is 3.5–3.7 kb in size. Both RNAs have 3′-terminal polyadenylate tracts and probably a VPg at the 5′ termini.
Virions contain one type of CP of 28.5–47 kDa. N- and C-terminal residues are positioned on the exterior of the virion. Mild trypsin treatment removes N- and C-terminal segments, leaving a trypsin-resistant core of about 24 kDa. Plant proteases may degrade the CP in vivo, as occurs in vitro during purification using some procedures or from certain hosts. All potyvirus CPs display significant aa sequence identity in the trypsin-resistant core, but little identity in their N and C-terminal segments.
The genomic RNA (each genomic RNA for the genus Bymovirus) encodes a single major polyprotein. This then undergoes co- and post-translational proteolytic processing by three viral-encoded proteinases to form individual gene products. Genomic RNA replicates via the production of a full-length negative sense RNA. While there are exceptions noted in the relevant genus descriptions, the polyprotein of the majority of monopartite viruses in the family is cleaved into ten products which show conservation of sequence and organisation. As shown in Figure 2, these products are:
P1: Of all the potyvirid proteins, P1 is the least conserved in sequence and the most variable in size. It plays a significant role in virus replication probably due to the stimulation of the gene silencing suppressor HC-Pro. A serine protease domain towards the C-terminus cleaves the P1 from the polyprotein, typically at Tyr/Phe-Ser.
HC-Pro (Helper Component-Protease): the HC-Pro protein has roles in suppression of gene silencing and in vector transmission. A cysteine protease domain towards the C-terminus cleaves it from the remainder of the downstream polyprotein, typically at Gly-Gly.
P3: Involved in virus replication and appears to be significant in host range and symptom development.
6K1: The function of this small protein is not known.
CI (Cylindrical Inclusion protein): This protein has helicase activity and accumulates in inclusion bodies in the cytoplasm of infected plant cells.
6K2: A small transmembrane protein probably anchoring the replication complex to the ER.
VPg (Viral Protein genome-linked): Attached to the 5′ terminus of the genome and belongs to a class of intrinsically disordered proteins. It plays multiple roles in the viral infection cycle. It is essential for virus replication and translation, interacting with one or several isoforms of the eIF4E translation initiation factor. It is involved in suppression of RNA silencing.
NIa-Pro: Serine-like cysteine protease responsible for cleavage of most sites in the polyprotein, typically at Gln/Glu-(Ser/Gly/Ala).
NIb: The RNA-dependent RNA polymerase.
CP: Viral coat protein that also has roles in virus movement, genome amplification and vector transmission.
Recent studies have shown the presence of an additional short ORF (PIPO=“pretty interesting potyvirus ORF”) embedded within the P3 cistron and expressed as a P3_PIPO fusion product via ribosomal frameshifting. This has now been identified throughout the family and has been shown to be essential for virus intercellular movement.
The viral proteins are moderately immunogenic; there are serological relationships among members. An epitope of the CP in the conserved internal trypsin-resistant core has been identified that is similar in most members of the family.
All members of the family Potyviridae form cytoplasmic cylindrical inclusion (CI) bodies during infection. The CI is an array of a 70 kDa viral protein that possesses ATPase and helicase activities. Some potyviruses induce nuclear inclusion bodies that are co-crystals of two viral-encoded proteins – NIa and NIb – present in equimolar amounts. The small nuclear inclusion (NIa) protein (49 kDa) is a polyprotein consisting of the VPg and proteinase. Amorphous inclusion bodies are also evident in the cytoplasm during certain potyvirus infections and represent aggregations of the protein HC-Pro and perhaps other non-structural proteins.
Some members have a narrow host range, most members infect an intermediate number of plants, and a few members infect species in up to 30 families. Transmission to most hosts is readily accomplished by mechanical inoculation. Many viruses are widely distributed. Distribution is aided by seed transmission in some cases.
Potyvirids are vectored by a variety of organisms. Members of the genera Potyvirus and Macluravirus have aphid vectors that transmit in a non-persistent, non-circulative manner. A helper component and a particular CP aa triplet (i.e., DAG for some potyviruses) are required for aphid transmission. Rymoviruses and tritimoviruses are transmitted by eriophyid mites, in a semi-persistent manner. Bymoviruses are transmitted by root-infecting vectors in the order Plasmodiophorales, once described as fungi but now classified as Cercozoa. Ipomoviruses appear to be transmitted by whiteflies.
Throughout the family, species are distinguished by the following criteria:
Type species Potato virus Y
The largest genus in the family contains viruses transmitted by aphids in a non-persistent manner.
Virions are flexuous filaments, 680–900 nm long and 11–13 nm wide, with helical symmetry and a pitch of about 3.4 nm. Particles of some viruses are longer in the presence of divalent cations than in the presence of EDTA.
Virion S20,w is 137–160S; density in CsCl is 1.31 g cm−3; E0.1%1 cm, 260 nm=2.4–2.7.
Virions contain a single molecule of linear, positive sense ssRNA, about 9.7 kb in size; virions contain 5% RNA by weight.
Virions contain a single CP, 30–47 kDa in size. The CP of most isolates of the type species, PVY, contains 267 aa.
The genome is organized as described earlier (Figure 2).
Virions are moderately immunogenic; there are serological relationships among many members. Some monoclonal antibodies react with most aphid-transmitted potyviruses. The CP aa sequence identity among aphid-transmitted viruses is 40–70%. Some viruses are serologically related to viruses in the genera Rymovirus and Bymovirus.
Many individual viruses have a narrow host range, but a few infect plant species in up to 30 host families. The viruses are transmitted by aphids in a non-persistent manner and are transmissible experimentally by mechanical inoculation. Some isolates are inefficiently transmitted by aphids and others are not transmissible by aphids at all. This is apparently due to mutations within the helper component and/or CP cistrons. Some viruses are seed-transmitted.
Algerian watermelon mosaic virus
Algerian watermelon mosaic virus-Algeria: H4
Alstroemeria mosaic virus
Alstroemeria mosaic virus-O1
Alternanthera mild mosaic virus
Alternanthera mild mosaic virus-Brazil
Amaranthus leaf mottle virus
Amaranthus leaf mottle virus-Italy
Amazon lily mosaic virus
Amazon lily mosaic virus-Japan
Angelica virus Y
Angelica virus Y-USA:g
Apium virus Y
Apium virus Y-USA: Ce
Araujia mosaic virus
Araujia mosaic virus-Argentina: ARG1973
Arracacha mottle virus
Arracacha mottle virus-Brazil:C17
Artichoke latent virus
Artichoke latent virus-California
Asparagus virus 1
Asparagus virus 1-Germany
Banana bract mosaic virus
Banana bract mosaic virus-Philippines
Basella rugose mosaic virus
Basella rugose mosaic virus-Taiwan:AC
Peace lily mosaic virus
Bean common mosaic necrosis virus
Bean common mosaic necrosis virus-USA:NL-3
Bean common mosaic virus
Bean common mosaic virus-NL4
Azuki bean mosaic virus
Blackeye cowpea mosaic virus
Dendrobium mosaic virus
Peanut stripe virus
Yam bean mosaic virus
Bean yellow mosaic virus
Bean yellow mosaic virus-MB4
Beet mosaic virus
Beet mosaic virus-Wa
Bidens mottle virus
Bidens mottle virus-Taiwan:B12
Sunflower chlorotic spot virus
Brugmansia suaveolens mottle virus
Brugmansia suaveolens mottle virus-Brazil
Butterfly flower mosaic virus
Butterfly flower mosaic virus-China:HZ
Calanthe mild mosaic virus
Calanthe mild mosaic virus-Japan
Canna yellow streak virus
Canna yellow streak virus-UK
Carnation vein mottle virus
Carnation vein mottle virus-Japan
Carrot thin leaf virus
Carrot thin leaf virus-Australia
Carrot virus Y
Carrot virus Y-Australia:Victoria
Celery mosaic virus
Celery mosaic virus-Netherlands
Ceratobium mosaic virus
Ceratobium mosaic virus-Australia:13
Chilli ringspot virus
Chilli ringspot virus-Vietnam:C8
Chilli veinal mottle virus
Chilli veinal mottle virus-Pepper vein banding virus
Chinese artichoke mosaic virus
Chinese artichoke mosaic virus-Japan
Clitoria virus Y
Clitoria virus Y-Australia:Queensland
Clover yellow vein virus
Clover yellow vein virus-30
Cocksfoot streak virus
Cocksfoot streak virus-Germany
Colombian datura virus
Colombian datura virus-Germany:Br1
Petunia flower mottle virus
Commelina mosaic virus
Commelina mosaic virus-Florida
Cowpea aphid-borne mosaic virus
Cowpea aphid-borne mosaic virus-Zimbabwe
Cowpea green vein banding virus
Cowpea green vein banding virus-Brazil
Cypripedium virus Y
Cypripedium virus Y-UK:CP
Daphne mosaic virus
Daphne mosaic virus-Czech Republic
Dasheen mosaic virus
Dasheen mosaic virus-China: M13
Vanilla mosaic virus
Datura shoestring virus
Datura shoestring virus-India:Simla
Diuris virus Y
Diuris virus Y-Australia
East Asian passiflora virus
East Asian passiflora virus-Japan:AO
Endive necrotic mosaic virus
Endive necrotic mosaic virus-Germany 1/85
Euphorbia ringspot virus
Euphorbia ringspot virus-USA
Freesia mosaic virus
Freesia mosaic virus-South Korea
Fritillary virus Y
Fritillary virus Y-China:Pan’an
Gloriosa stripe mosaic virus
Gloriosa stripe mosaic virus-Netherlands
Groundnut eyespot virus
Groundnut eyespot virus-Ivory Coast
Guinea grass mosaic virus
Guinea grass mosaic virus-Ivory Coast
Hardenbergia mosaic virus
Hardenbergia mosaic virus-Australia: BB-6
Helenium virus Y
Helenium virus Y-Germany
Henbane mosaic virus
Henbane mosaic virus-Hungary:PHYS/H
Hibbertia virus Y
Hibbertia virus Y-Australia: New South Wales
Hippeastrum mosaic virus
Hippeastrum mosaic virus-Amaryllis
Hyacinth mosaic virus
Hyacinth mosaic virus-Netherlands
Iris fulva mosaic virus
Iris fulva mosaic virus-USA:Massachusetts
Iris mild mosaic virus
Iris mild mosaic virus-New Zealand:DC4a
Iris severe mosaic virus
Iris severe mosaic virus-Netherlands
Japanese yam mosaic virus
Japanese yam mosaic virus-mild
Johnsongrass mosaic virus
Johnsongrass mosaic virus-Australia
Kalanchoë mosaic virus
Kalanchoë mosaic virus-Netherlands:F39
Konjac mosaic virus
Konjac mosaic virus-Japan: F
Zantedeschia mosaic virus
Japanese hornwort mosaic virus
Leek yellow stripe virus
Leek yellow stripe virus-China:Yuhang
Lettuce mosaic virus
Lettuce mosaic virus-E
Lily mottle virus
Lily mottle virus-China:Sb
Lycoris mild mottle virus
Lycoris mild mottle virus-Taiwan
Maize dwarf mosaic virus
Maize dwarf mosaic virus-Bulgaria
Malva vein clearing virus
Malva vein clearing virus-Italy:DS-Ba-01
Meadow saffron breaking virus
Meadow saffron breaking virus-France
Moroccan watermelon mosaic virus
Moroccan watermelon mosaic virus-Tunisia:TN05-76
Narcissus degeneration virus
Narcissus degeneration virus-China:Zhangzhou
Narcissus late season yellows virus
Narcissus late season yellows virus-China:Hangzhou 2
Narcissus yellow stripe virus
Narcissus yellow stripe virus-China:Zhangzhou
Nerine yellow stripe virus
Nerine yellow stripe virus-Netherlands:Ne800
Nothoscordum mosaic virus
Nothoscordum mosaic virus-Canary Islands
Onion yellow dwarf virus
Onion yellow dwarf virus-China:Yuhang
Ornithogalum mosaic virus
Ornithogalum mosaic virus-O
Ornithogalum virus 2
Ornithogalum virus 2-Japan:Akita, Oga
Ornithogalum virus 3
Ornithogalum virus 3-Japan
Papaya leaf distortion mosaic virus
Papaya leaf distortion mosaic virus-Japan:P
Papaya ringspot virus
Papaya ringspot virus-Hawaii
Parsnip mosaic virus
Parsnip mosaic virus-UK:Scotland
Passiflora chlorosis virus
Passiflora chlorosis virus-LAJ-2006
Passion fruit woodiness virus
Passion fruit woodiness virus-Australia:MU2
Pea seed-borne mosaic virus
Pea seed-borne mosaic virus-DPD1
Peanut mottle virus
Peanut mottle virus-M
Pennisetum mosaic virus
Pennisetum mosaic virus-China:B
Pepper mottle virus
Pepper mottle virus-California
Pepper severe mosaic virus
Pepper severe mosaic virus-South Korea
Pepper veinal mottle virus
Pepper veinal mottle virus-P
Pepper yellow mosaic virus
Pepper yellow mosaic virus-Brazil:Pi-15
Peru tomato mosaic virus
Peru tomato mosaic virus-Peru:PPK13
Pfaffia mosaic virus
Pfaffia mosaic virus-Brazil
Pleione virus Y
Pleione virus Y-Australia
Plum pox virus
Plum pox virus-NAT
Pokeweed mosaic virus
Pokeweed mosaic virus-USA
Potato virus A
Potato virus A-Hungary: B11
Tamarillo mosaic virus
Potato virus V
Potato virus V-UK:DV 42
Potato virus Y
Potato virus Y-France:O
Potato virus Y-Hungary:N
Potato virus Y-France:C
Bidens mosaic virus
Ranunculus leaf distortion virus
Ranunculus leaf distortion virus-Italy:RN122
Ranunculus mild mosaic virus
Ranunculus mild mosaic virus-Italy:RN129
Ranunculus mosaic virus
Ranunculus mosaic virus-Italy:RN136
Rhopalanthe virus Y
Rhopalanthe virus Y-Australia
Sarcochilus virus Y
Sarcochilus virus Y-Australia
Scallion mosaic virus
Scallion mosaic virus-China:Hangzhou
Shallot yellow stripe virus
Shallot yellow stripe virus-China:ZQ2
Sorghum mosaic virus
Sorghum mosaic virus-China:Xiaoshan
Soybean mosaic virus
Soybean mosaic virus-N
Spiranthes mosaic virus 3
Spiranthes mosaic virus 3-USA
Sugarcane mosaic virus
Sugarcane mosaic virus-China:Hangzhou
Sunflower mosaic virus
Sunflower mosaic virus-USA:Texas
Sweet potato feathery mottle virus
Sweet potato feathery mottle virus-S
Sweet potato latent virus
Sweet potato latent virus-Taiwan
Sweet potato mild speckling virus
Sweet potato mild speckling virus-Argentina
Sweet potato virus 2
Sweet potato virus 2-Nigeria
Sweet potato virus G
Sweet potato virus G-Peru:Hua2
Telfairia mosaic virus
Telfairia mosaic virus-Nigeria
Telosma mosaic virus
Telosma mosaic virus-Vietnam:Hanoi
Thunberg fritillary mosaic virus
Thunberg fritillary mosaic virus-China: Ningbo
Tobacco etch virus
Tobacco etch virus-HAT
Tobacco vein banding mosaic virus
Tobacco vein banding mosaic virus-China:YND
Tobacco vein mottling virus
Tobacco vein mottling virus-S
Tradescantia mild mosaic virus
Tradescantia mild mosaic virus-Italy:IFA195
Tropaeolum mosaic virus
Tropaeolum mosaic virus-Ecuador:Mashua
Tuberose mild mosaic virus
Tuberose mild mosaic virus-Taiwan
Tuberose mild mottle virus
Tuberose mild mottle virus-China:Hangzhou
Tulip breaking virus
Tulip breaking virus-India
Tulip mosaic virus
Tulip mosaic virus-Japan
Turnip mosaic virus
Turnip mosaic virus-UK1
Twisted-stalk chlorotic streak virus
Twisted-stalk chlorotic streak virus-Alaska:Denali 2001
Vallota mosaic virus
Vallota mosaic virus-USA:Beltsville
Watermelon leaf mottle virus
Watermelon leaf mottle virus-Florida
Watermelon mosaic virus
Watermelon mosaic virus-Fr
Wild potato mosaic virus
Wild potato mosaic virus-Peru
Wild tomato mosaic virus
Wild tomato mosaic virus-Vietnam: Laichau
Wisteria vein mosaic virus
Wisteria vein mosaic virus-China:Beijing
Yam mild mosaic virus
Yam mild mosaic virus-Papua New Guinea
Yam mosaic virus
Yam mosaic virus-Ivory Coast
Zantedeschia mild mosaic virus
Zantedeschia mild mosaic virus-Taiwan
Zea mosaic virus
Zea mosaic virus-Israel
Zucchini yellow fleck virus
Zucchini yellow fleck virus-Italy
Zucchini yellow mosaic virus
Zucchini yellow mosaic virus-Taiwan:TN3
Species names are in italic script; names of strains, isolates and synonyms are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.
* Partial sequence including the coat protein; complete genome sequence not available.
Ammi majus latent virus
Anemone mosaic virus
Arisaema potyvirus 1
Arisaema potyvirus 2
Begonia flower breaking virus
Calla lily latent virus
Catharanthus mosaic virus
Chickpea yellow mosaic virus
Christmas bell potyvirus
Delphinium vein-clearing virus
Ecuadorian rocoto virus
Impatiens flower break virus
Lupin mosaic virus
Muscari mosaic virus
Omphalodes virus Y
Ornamental onion stripe mosaic virus
Ornithogalum necrotic mosaic virus
Ornithogalum stripe mosaic virus
Ornithogalum virus 4
Panax virus Y
Passiflora foetida virus Y
Siratro 1 virus Y
Siratro 2 virus Y
Snowdrop virus Y
Sunflower chlorotic mottle virus
Stenomesson mosaic virus
Sweet potato virus C
Trillium crinkled leaf virus
Vanilla distortion mosaic virus
Veltheimia mosaic virus
Veltheimia virus Y
Verbena virus Y
Type species Blackberry virus Y
This is a monotypic genus. The single species is distinguished from all other members of the family by having a very large P1 protein (83.6 k Da) containing an AlkB domain. It is also phylogenetically distinct.
Virions are flexuous filaments 800×11–15 nm in size.
Virions contain a single molecule of linear positive sense ssRNA with a 3′-poly(A) terminus. Virion RNA is about 11 kb in size.
There is a single CP of 40.9 kDa.
Apart from the size of the P1, the genome organization is identical to that of most monopartite viruses in the family Potyviridae (Figure 2).
The virus could not be detected by a universal potyvirus monoclonal antibody but there are no additional data.
The virus has been reported only from wild and cultivated blackberry (Rubus sp.) where it is often symptomless but is also a component of a complex of viruses. It is not known to cause symptoms in any herbaceous test host.
The virus is presumed to be transmitted by an aerial vector that has not yet been identified.
Blackberry virus Y
Blackberry virus Y-Arkansas 3
Species names are in italic script; names of isolates are in roman script. Sequence accession numbers [ ] and assigned abbreviations ( ) are also listed.
Type species Sweet potato mild mottle virus
Ipomoviruses are distinguished from other genera by their mode of transmission (whiteflies) and by phylogenetic analyses.
Virions are flexuous filaments 800–950 nm long.
Virion S20,w is 155S for sweet potato mild mottle virus (SPMMV).
Virions contain a positive sense ssRNA, with a 3′-poly(A) terminus.
The viral CP is a single polypeptide of 302–378 aa (35–41 kDa).
Ipomovirus genomes consist of 9069–10818 nt excluding the 3′-terminal poly(A) tail and encode a polyprotein of 2902–3456 aa (Figure 3). These viruses exhibit unusual structural variability. The structure and organization of the SPMMV genome is similar to Potyvirus, but some motifs of HC-Pro and CP characteristic of Potyvirus are incomplete or missing, which may account for its vector relations. The unusually large P1 (83 kDa) of SPMMV contains no obvious AlkB domain and hence differs from Brambyvirus. Cucumber vein yellowing and squash vein yellowing viruses (CVYV and SqVYV) differ from SPMMV by containing two P1-like serine proteases (P1a and P1b) but no HC-Pro. P1b functions as a suppressor of RNA silencing. Cassava brown streak virus (CBSV) differs from SPMMV by having no HC-Pro and, also, from CVYV and SqVYV by having only P1b which suppresses silencing. Additionally, CBSV contains a Maf/HAM1-like sequence recombined into the NIb/CP junction which can accommodate heterologous genes in engineered infectious potyvirus clones. Homology of HAM1h with cellular Maf/HAM1 NTP pyrophosphatases suggests that HAMh1 might intercept non-canonical NTPs to reduce mutation rates of viral RNA.
Moderately immunogenic. No serological relationships with other members of the family Potyviridae have been found.
The natural host range of SPMMV is wide, with more than nine families susceptible, whereas the host range of CBSV, CVYV and SqVYV is less known apart from the hosts which they have been found to infect in the field.
CBSV, CVYV and SqVYV are transmitted by the whitefly Bemisia tabaci in a non-persistent manner. B. tabaci may also be the vector of SPMMV, but this is not fully confirmed. All ipomoviruses are transmissible experimentally by mechanical inoculation and by grafting.
Cassava brown streak virus
Cassava brown streak virus-Tanzania:KOR6
Cucumber vein yellowing virus
Cucumber vein yellowing virus-Spain:ALM32
Squash vein yellowing virus
Squash vein yellowing virus-Florida
Sweet potato mild mottle virus
Sweet potato mild mottle virus-East Africa
Ugandan cassava brown streak virus
* Two strains sharing 87% nucleotide sequence identity.
Type species Maclura mosaic virus
Macluraviruses resemble members of the genus Potyvirus in their transmission by aphids but virions are slightly shorter. They form a distinct group in phylogenetic analyses and have different polyprotein consensus cleavage sites.
Virions are flexuous filaments mostly 650–675 nm×13–16 nm.
Virion S20,w is 155–158S; density in CsCl is 1.31–1.33 g cm−3.
Virions contain one molecule of linear positive sense, ssRNA. RNA is about 8.0 kb.
Macluraviruses have a single CP species of 33–34 kDa.
Complete genomes of macluraviruses are not yet available. The aa sequences of macluravirus CPs show limited (14–23%) identity with CP sequences of some aphid-transmitted potyviruses. Macluraviruses show significant aa sequence identity in portions of the replicase protein with viruses in other genera of the family Potyviridae. The macluraviruses seem to have a genome organization and replication strategy typical of viruses in the family Potyviridae.
Moderately immunogenic. No serological relationships to members of the genus Potyvirus have been found except for a weak reaction between Maclura mosaic virus (MacMV) and bean yellow mosaic virus.
Current information suggests that most viruses have a narrow host range, infecting species in up to nine host families.
The viruses are transmitted by aphids in a non-persistent manner and experimentally by mechanical inoculation.
Alpinia mosaic virus
Alpinia mosaic virus-Taiwan
Cardamom mosaic virus
Cardamom mosaic virus-India:Yelsur
Maclura mosaic virus
Maclura mosaic virus-UK
Chinese yam necrotic mosaic virus
Chinese yam necrotic mosaic virus-Japan
Narcissus latent virus
Narcissus latent virus-New Zealand
Ranunculus latent virus
Ranunculus latent virus-RN128
Yam chlorotic necrotic mosaic virus
Type species Ryegrass mosaic virus
This genus contains only three viruses presumably transmitted by host-adapted populations of eriophyid mite species in a semi-persistent manner. The rymoviruses share a reciprocal monophyletic relationship with species of the genus Potyvirus (see Figure 6).
Virions are flexuous filaments 690–720 nm×11–15 nm in size.
Virion density in CsCl is 1.325 g cm-3 (for ryegrass mosaic virus, RGMV). Virion S20,w is 165–166S for most members.
Virions contain a single molecule of linear positive sense ssRNA with a 3′-poly(A) terminus. Virion RNA is about 9.5 kb in size.
Rymoviruses have one type of CP, with a theoretical Mr of 35,482 Da and an apparent Mr estimated by Western blots of 45 kDa for RGMV.
The complete genome sequences available for two isolates of RGMV and one each of Agropyron mosaic virus (AgMV) and Hordeum mosaic virus (HoMV) indicate that rymoviruses have a genome organization (see Figure 2) and replication strategy similar to other species of the Potyviridae with monopartite genomes.
Particles of most rymoviruses are moderately immunogenic. HoMV and AgMV are serologically related.
Most rymoviruses have limited but widespread host ranges within the family Gramineae but some have relatively narrow host ranges.
Transmission by eriophyid mites and mechanical transmission have been reported for most members. The eriophyid mites transmitting rymoviruses are different from those transmitting tritimoviruses. The cereal rust mite Abacarus hystrix transmits both RGMV and AgMV, but only the former is efficiently transmitted. No vector is known for HoMV. Recent studies have revealed that host-associated populations of A. hystrix represent a species complex.
Agropyron mosaic virus
Agropyron mosaic virus-USA:ND402
Hordeum mosaic virus
Hordeum mosaic virus-ATCC PV81
Ryegrass mosaic virus
Ryegrass mosaic virus-Denmark
Type species Wheat streak mosaic virus
Tritimoviruses are transmitted by mites (but different from those that transmit rymoviruses). They form a distinctive phylogenetic cluster.
Virions are flexuous filaments 690–700 nm long.
Virion S20,w is 166S for wheat streak mosaic virus (WSMV).
Virions contain a positive sense ssRNA, about 9.4–9.6 kb in size, with a 3′-poly(A) terminus.
The viral CP is a single peptide of about 349 aa for WSMV and 320 aa for brome streak mosaic virus (BrSMV). The Mr estimated by electrophoresis is about 42 kDa.
The WSMV genome consists of 9384 nt excluding the 3′-terminal poly(A) tail. Sequence analysis reveals an ORF of 3035 aa. The structure and organization of the WSMV genome is similar to those of other members of the family Potyviridae (see Figure 2) except the bymoviruses. Most known potyvirus motifs are present in the polyprotein of WSMV. However, motifs in the putative helper-component and CP of BrSMV are incomplete or missing, which may account for different vector relations of the tritimoviruses. The WSMV CP sequence shows limited (22-25%) identity with CP sequences of some aphid-transmitted potyviruses. WSMV shows significant aa sequence identity with aphid-transmitted potyviruses in the cylindrical inclusion protein and portions of the nuclear inclusion proteins. WSMV RNA has been translated in vitro into several large proteins immunoprecipitable with WSMV CP antiserum, suggesting that WSMV uses a proteolytic processing strategy to express functional proteins such as the CP. Antiserum to TEV 58 kDa nuclear inclusion protein also reacts with in vitro translation products of WSMV. An in vitro translation product is precipitated with antiserum to HC-Pro helper component of an isolate of the species Tobacco vein mottling virus. Comparative sequence analyses show similarities with other members of the family Potyviridae, but these are limited to the nine mature proteins. WSMV is especially susceptible to proteinases in planta and has CP molecules of 42, 36 and 32 kDa; the two smaller proteins are parts of the 42 kDa protein.
Moderately immunogenic. WSMV and oat necrotic mottle virus (ONMV) are serologically related to each other, but not to the other members of the family Potyviridae.
The viruses only affect hosts in the Gramineae but while WSMV has a wide host range BrSMV and ONMV have narrow ones.
WSMV and BrSMV are transmitted by eriophyid mites in a semi-persistent manner. HC-Pro of WSMV is required for mite transmission. All definitive tritimoviruses are transmissible experimentally by mechanical inoculation.
Brome streak mosaic virus
Brome streak mosaic virus-France-11-Cal
Oat necrotic mottle virus
Oat necrotic mottle virus-Type-NE
Wheat Eqlid mosaic virus
Wheat Eqlid mosaic virus-Iran
Wheat streak mosaic virus
Wheat streak mosaic virus-Sidney 81
Yellow oat-grass mosaic virus
Type species Barley yellow mosaic virus
Compared with other viruses in the family, members of the genus Bymovirus are distinct in having a divided (bipartite) genome and in being transmitted by the root-infecting parasite, Polymyxa graminis (Plasmodiophorales, a fungoid protist).
Virions are flexuous filaments of two modal lengths, 250–300 nm and 500-600 nm; both are 13 nm in width (Figure 4).
Virion density in CsCl is 1.28–1.30 g cm−3.
Virions contain two molecules of linear positive sense, ssRNA. RNA-1 is 7.5–8.0 kb and RNA-2 is 3.5–4.0 kb; RNA makes up 5% by weight of particles. There is little base sequence identity between the two RNAs except in the 5′ UTR.
Virions have a single CP of 28.5–33 kDa. The CP of barley yellow mosaic virus isolates has 297 aa.
The two RNA molecules are translated initially into precursor polypeptides from which functional proteins are derived by proteolytic processing (Figure 5). The organization of RNA1 is similar to that of other potyviruses but without the P1 and HC-Pro proteins. The RNA2 polyprotein is unique to bymoviruses although the first (ca. 28 kDa) protein from RNA-2 has aa domains with sequence similarities to the potyvirus protein HC-Pro. The larger protein of RNA2 is believed to have a role in vector transmission.
The viral proteins are moderately immunogenic; serological relationships exist among most members (except barley mild mosaic virus). The CP aa sequence identity among members is 35–74%.
There are characteristic pinwheel-like inclusions and membranous network structures are formed in the cytoplasm of infected plant cells. No nuclear inclusions are found.
The host range of member viruses is narrow, restricted to the host family Gramineae. Each species has a very restricted host range; for example, the barley-infecting species do not infect wheat and vice versa.
These viruses are transmitted by Polymyxa graminis in a persistent manner, surviving in resting spores as long as these remain viable; it is transmissible experimentally by mechanical inoculation, sometimes with difficulty.
Barley mild mosaic virus
Barley mild mosaic virus-fungally transmissible UK isolate
Barley yellow mosaic virus
Barley yellow mosaic virus-IIa
Oat mosaic virus
Oat mosaic virus-UK
Rice necrosis mosaic virus
Rice necrosis mosaic virus-Japan
Wheat spindle streak mosaic virus
Wheat spindle streak mosaic virus-France
Wheat yellow mosaic virus
Wheat yellow mosaic virus-Japan
* Partial sequence of RNA1, including the coat protein; complete genome sequence not available.
Spartina mottle virus
Spartina mottle virus-Germany
Sugarcane streak mosaic virus
Sugarcane streak mosaic virus-Pakistan
Tomato mild mottle virus
Tomato mild mottle virus-Yemen
Tomato mild mottle virus is most closely related to members of the genus Ipomovirus but is transmitted by aphids in a non-circulative manner, whereas ipomoviruses are transmitted by the whitefly Bemisia tabaci. No vectors have been identified for the other unassigned members of the family.
Triticum mosaic virus-Kansas isolate U06-123
There is a current proposal to make Triticum mosaic virus, recently described in the USA and transmitted by the same mite vector as tritimoviruses, the type species of a new genus, Poacevirus. If accepted, this genus would also contain the unassigned species Sugarcane streak mosaic virus, which is clearly related.
Phylogenetic relationships within the family are depicted in Figures 6 and 7.
Viruses in the family Potyviridae have similarity to members of the order Picornavirales. In particular, the genomes have a VPg at their 5′ termini and a poly(A) tract at their 3′ termini. Their genomes are expressed initially as high molecular weight polyprotein precursors which are processed by virus-encoded proteases. Gene products involved in replication are conserved in gene order and gene sequence. However, members of the Picornavirales have isometric particles, a much smaller VPg and a different type of helicase. There are also some sequence similarities to members of the family Hypoviridae.
Bramby: from bramble, the host of the type species.
Bymo: from barley yellow mosaic.
Ipomo: from Ipomea and mosaic.
Maclura: the genus name of the host of the type species.
Poty: from potato virus Y.
Rymo: from ryegrass mosaic.
Tritimo: from Triti*** and mosaic.
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Adams, M.J., Zerbini, F.M., French, R., Rabenstein, F., Stenger, D.C. and Valkonen, J.P.T.