|
Type Species |
(CRSV) |
Virions sediment in sucrose gradients as a single band of S20w 126-135S. The genome is in two genomic RNAs of 3.9 and 1.5 kb. The first ORF1 encoding the polymerase is interrupted by a ribosomal frameshifting event yielding a pre-frameshift Mr 27 
103 protein and a Mr 88 103 frameshift polypeptide. The CP possessing a protruding domain, is encoded by the 3
-proximal ORF on RNA1 and is expressed from a 1.5 kb sgRNA in vivo. The ORF for the phylogenetically distinct Mr 34-35 103 movement protein is in the monocistronic RNA2. Species are transmitted through the soil without the aid of a biological vector.
Virions are not enveloped. Virions are 32-35 nm in diameter and have a T = 3 icosahedral symmetry (Fig. 7). The isometric nucleocapsids have an obvious regular surface structure giving a granular appearance in the electron microscope. The surface capsomer arrangement is not obvious. Virions are composed of 180 protein subunits, but the detailed structure is not known. However, based on similarity of CP sequence, it is predicted that the virion is similar in structure to those of species in the genera Carmovirus and Tombusvirus. Each subunit is predicted to fold into three distinct structural domains: R, the N-terminal internal domain interacting with RNA; S, the shell domain constituting the capsid backbone; and P, the protruding C-terminal domain. P domains are clustered in pairs to form 90 projections.
Physicochemical and Physical Properties
Virions sediment as one component in sucrose with S20w of 126-135S. The buoyant density in CsCl is 1.363-1.366 g/cm3, and the virion Mr is 8.6 106. Particles exhibit an A260/A280 ratio of 1.67 and a thermal inactivation point between 80-90°C. A longevity in vitro of around 10 weeks has been reported for most species. Virions are insensitive to ether, chloroform and non-ionic detergents. Virions are stable at pH 6 and alkaline conditions (pH 7-8) induce particle swelling. Virions are stabilized by divalent cations.
Virions contain two molecules of infectious linear positive sense ssRNA. Genomic RNA1 is 3876-3940 nts and RNA2 is between 1412-1449 nts in size. The 5-end of each RNA is capped with m7GpppA. The RNAs do not contain a 3-terminal poly(A) tract or a tRNA-like structure. It is assumed that the virion packages only one copy of each genomic RNA. There is no evidence that the sgRNAs are packaged into virions. Three virus-specific dsRNA species are found in infected cells. The largest and smallest dsRNAs correspond to the genomic RNA1 and RNA2, respectively. The smallest dsRNA corresponds to a sgRNA of 1.5 kb representing the 3 portion of genomic RNA1.
Virions are composed of 180 copies of a single CP of 339 amino acid (Mr 37-38 103).
None reported.
None reported.
Genome Organization and Replication
Only the 5-terminal 6 nts and 3 terminal 27 nts are identical in RNA1 and RNA2 (Fig. 8). The 3 27 nts are predicted to form a stem-loop structure. RNA1 contains two ORFs. ORF1 is capable of encoding a Mr 27 103 protein. A -1 ribosomal frameshift event at the canonical shifty heptanucleotide allows translation to continue into ORF 1FS in about 5% of the times the RNA is translated to yield a Mr 88 103 protein. Both the Mr 27 and 88 103 proteins are observed in vivo and are made by translation of virion RNA in vitro. The ORF1 and ORF1FS encoded proteins form the viral polymerase. ORF2 encodes the Mr 37-38 103 CP. This ORF is expressed in vivo from the 1.5 kb sgRNA. ORF3 on RNA2 encodes the Mr 34-35 103 movement protein.
The viruses are moderately to highly immunogenic. Various serologically distinct strains have been identified. Antisera yield a single precipitin line in agar gel-diffusion assays. Monoclonal antibodies have been identified that cross-react between species.
In nature dianthoviruses have moderately broad natural host ranges restricted to dicotyledonous plants. In the laboratory, the experimental host range is much broader, and includes a wide range of herbaceous species in the families Solanaceae, Leguminosae, Cucurbitaceae, and Compositae. Species infect a larger number of plants locally (non-systemically).
The viruses are readily transmitted by mechanical inoculation; they are not known to be seed-transmitted. The viruses are not transmitted by insects, nematodes, or soil-inhabiting fungi. However, viruses are readily transmitted through the soil without the aid of a biological vector.
Dianthoviruses, with the possible exception of FNSV, which appears to be tropical in range, are widespread throughout the temperate regions of the world.
None reported.
List of Species Demarcation Criteria in the Genus
The list of species demarcation criteria in the genus is:
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Extent of serological relationship as determined by immunodiffusion and/or ELISA, |
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Extent of sequence identity between relevant gene products, |
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Less than 79% amino acid sequence identity of the CP, |
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Less than 54% amino acid sequence identity of the polymerase, |
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Ability to form pseudorecombinants with the two RNA components, |
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Transmission by a fungal vector, |
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Natural host range, |
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Artificial host range reactions. |
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:
|
Carnation ringspot virus (21, 308) |
[M88589, L18870] |
(CRSV) |
|
Red clover necrotic mosaic virus (181) |
[J04357, X08021] |
(RCNMV) |
|
Sweet clover necrotic mosaic virus (321) |
[L07884, S46027, S46028] |
(SCNMV) |
Tentative Species in the Genus
|
Furcraea necrotic streak virus |
(FNSV) |
|
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