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Type Species |
(CLV) |
Virions are slightly flexuous filaments, 610-700 nm in length and 12-15 nm in diameter. They have helical symmetry with a pitch of about 3.4 nm (Fig. 1).
Physicochemical and Physical Properties
Virion Mr is about 60 106. Virion S20w is 147-176S, and the buoyant density in CsCl solutions is 1.3 g/cm3.
Virions contain a single molecule of linear ssRNA of 7.4-7.7 kb (although those of Potato virus M (PVM) and Blueberry scorch virus (BBScV) are 8530 and 8514 nts, respectively). Some species also have two sgRNAs of 2.1 to 3.3 kb and 1.3 to 1.6 kb, which are possibly encapsidated in shorter particles. The genomic RNAs have a 3 poly(A) tract and, probably, a 5-cap. They contain six ORFs. The nucleotide sequence or partial sequence of twelve carlavirus RNAs has been determined.
Virions contain a single polypeptide of Mr 31-36 103.
None reported.
None reported.
Genome Organization and Replication
The genomic RNAs of PVM and BBScV, the better characterized species, each contains six ORFs; PVM RNA has non-coding sequences of 75 nts at the 5-terminus, 70 nts followed by a poly(A) tail at the 3-terminus and 38 and 21 nts between the three large blocks of coding sequences (Fig. 2).
ORF1 encodes a polypeptide of 223 103 which is the viral replicase; ORFs 2, 3 and 4 form the triple gene block and encode polypeptides of 25 103, 12 103 and 7 103 which facilitate virus movement. ORF5 encodes the capsid protein (CP) of 34 103 and overlaps ORF5, which encodes a cysteine-rich protein of 11-16 103. The gene arrangement of other incompletely sequenced carlaviruses is similar. The proteins encoded by the triple gene block facilitate cell-to-cell movement of virus. The 34 103 polypeptide is the CP. The function of the 11-16 103 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 and/or viral RNA replication.
The viruses 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; however, one species (Cowpea mild mottle virus, CPMMV) is transmitted by whiteflies (Bemisia tabaci). Three of the viruses (Pea streak virus, PeSV; Red clover vein mosaic virus, RCVMV and CPMMV) naturally occurring in leguminous species are seedborne. All the viruses are mechanically transmissible; some (e.g., Carnation latent virus, CLV and Potato virus S, PVS) are sufficiently infectious to be so transmitted naturally.
The geographic 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 that transmitted by whiteflies 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 which are seen by light microscopy 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
List of Species Demarcation Criteria in the Genus
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. The core region (i.e., excluding the N- and C-termini) of the CPs of distinct species have less than 68% sequence homology with those of other carlaviruses; strains of individual viruses have 75-90% homology.
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, CMI/AAB description numbers ( ), genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
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Aphid-borne carlaviruses: | ||
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American hop latent virus (262) |
(AHLV) | |
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Blueberry scorch virus |
[L25658] |
(BlScV) |
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Cactus virus 2 |
(CV-2) | |
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Caper latent virus |
(CapLV) | |
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Carnation latent virus (61) |
[X55331, X55897, U43905] |
(CLV) |
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Chrysanthemum virus B (110) |
[S60150] |
(CVB) |
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Dandelion latent virus |
(DaLV) | |
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Elderberry symptomless virus |
(ESLV) | |
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(Elderberry virus A) |
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Garlic common latent virus |
[S60150] |
(GarCLV) |
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Garlic latent virus |
[AB004458, AB004565-67, AB004684-86] |
(GarLV) |
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Helenium virus S (265) |
[D10454, S71594] |
(HVS) |
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Honeysuckle latent virus (289) |
(HnLV) | |
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Hop latent virus (261) |
(HpLV) | |
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Hop mosaic virus (241) |
(HpMV) | |
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Hydrangea latent virus |
(HdLV) | |
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Kalanchoe latent virus |
(KLV) | |
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Lilac mottle virus |
(LiMoV) | |
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Lily symptomless virus (96) |
[X15343, D43801, AF01594] |
(LSV) |
|
(Alstroemeria carlavirus) |
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Mulberry latent virus |
(MLV) | |
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Muskmelon vein necrosis virus |
(MuVNV) | |
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Nerine latent virus |
(NeLV) | |
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(Hippeastrum latent virus) |
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Passiflora latent virus |
(PLV) | |
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Pea streak virus (112) |
(PeSV) | |
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(Alfalfa latent virus) (211) |
||
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Poplar mosaic virus (75) |
[X65102, D13364, X97683, X97765] |
(PopMV) |
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Potato virus M (87) |
[X53062, X57440, D144449, AF23877] |
(PVM) |
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Potato virus S (60) |
[D00461, S45593] |
(PVS) |
|
(Pepino latent virus) |
||
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Red clover vein mosaic virus (22) |
(RCVMV) | |
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Shallot latent virus (250) |
[AB004456-57, AB004544, AB4802-03] |
(SLV) |
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Sint-Jem’s onion latent virus |
(SJOLV) | |
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Strawberry pseudo mild yellow edge virus |
(SPMYEV) | |
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Whitefly-transmitted carlaviruses: | ||
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Cowpea mild mottle virus |
[AF024628-29] |
(CPMMV) |
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(Bean angular mosaic virus) |
||
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(Groundnut crinkle virus) |
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(Psophocarpus necrotic mosaic virus) |
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(Tomato pale chlorosis virus) |
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(Voandzeia mosaic virus) |
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Tentative Species in the Genus
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Anthriscus latent virus |
(AntLV) |
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Arracacha latent virus |
(ALV) |
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Artichoke latent virus M |
(ArLVM) |
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Artichoke latent virus S |
(ArLVS) |
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Butterbur mosaic virus |
(ButMV) |
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Caraway latent virus |
(CawLV) |
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Cardamine latent virus |
(CaLV) |
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Cassia mild mosaic virus |
(CasMMV) |
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Chicory yellow blotch virus |
(ChYBV) |
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Chinese yam necrotic mosaic virus |
(ChYNMV) |
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Cole latent virus |
(CoLV) |
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Cynodon mosaic virus |
(CynMV) |
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Daphne virus S |
(DVS) |
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Dulcamara virus A |
(DuVA) |
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Dulcamara virus B |
(DuVB) |
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Eggplant mild mottle virus (Eggplant virus) |
(EMMV) |
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Euonymus mosaic virus |
(EuoMV) |
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Fig virus S |
(FVS) |
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Fuchsia latent virus |
(FLV) |
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Garlic mosaic virus |
(GarMV) |
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Gentiana viruslatent virus |
(GenLV) |
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Gynura latent virus |
(GyLV) |
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(Chrysanthemum virus B?) |
|
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Helleborus mosaic virus |
(HeMV) |
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Impatiens latent virus |
(ILV) |
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Lilac ringspot virus |
(LiRSV) |
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Plantain virus 8 |
(PlV-8) |
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Prunus virus S |
(PruVS) |
|
Southern potato latent virus |
(SoPLV) |
|
White bryony mosaic virus |
(WBMV) |
Phylogenetic Relationships within the Genus
Not available.
The composition of the 12 103, 7 103 and 25 103 polypeptides of the triple gene block of carlaviruses is very similar to that of comparable polypeptides produced by potexviruses; these polypeptides also have homologies with proteins produced by Barley stripe mosaic virus and Beet necrotic yellow vein virus.
The replicase of carlaviruses is a papain-like proteinase with sequence similarity to comparable replicases of potexviruses, furoviruses, capilloviruses and tymoviruses, especially the latter which, like that of carlaviruses, is capable of autoproteolysis.
Virions of Narcissus latent virus (NLV) are filamentous and about 650 nm long. It was previously considered to be a carlavirus. However, it differs from carlaviruses in inducing the formation of intracellular inclusions (“pinwheels”) and in having a CP of 46 103; it is thus now better placed in the genus Macluravirus (family Potyviridae), together with Maclura mosaic virus, to which it is serologically related.
Brown streak symptoms in cassava (Manihot esculenta) were previously thought to be induced by a carlavirus tentatively designated Cassava brown streak-associated virus. In recent extensive studies, no carlavirus was detected in affected cassava plants (G.D. Foster, personal communication); such plants, however, consistently contained a newly recognized virus (now designated Cassava brown streak virus; CBSV) which induces the formation of cytoplasmic intracellular inclusions and has filamentous particles containing single-stranded RNA having significant sequence homology with that of Sweet potato mild mottle virus. CBSV is thus probably a species of the genus Ipomovirus (Potyviridae)
Carla: siglum from carnation latent.
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