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Type Species |
(ASPV) |
Virions are flexuous filaments, approximately 800 
12 nm, with helical symmetry exhibiting a surface pattern with cross-banding and longitudinal lines (Fig. 1). Particles of some species such as, Apple stem pitting virus (ASPV) and Cherry green ring mottle virus, (CGRMV) show a tendency to end-to-end aggregation.
Physicochemical and Physical Properties
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 sulphate. CGRMV virions resist organic solvents and are stable in cesium sulphate.
Virions contain a single molecule of positive sense ssRNA, polyadenylated at the 3
terminus. The genome of the tentative species CGRMV is capped at the 5 terminus. The complete nucleotide sequence of ASPV (9.3 kb), Rupestris stem pitting-associated virus (RSPaV) (8.7 kb), and CGRMV (8.4 kb) are available.
The viral capsid of all species is composed of a single polypeptide with a size ranging from 28 103 (RSPaV), to 30 103 (CGRMV), to 44 103 (ASPV). Non structural proteins consist of a large polypeptide (230-247 103) containing the methyltransferase, helicase, and viral RNA-dependent RNA polymerase (RdRp) signatures, a 25 103 polypeptide with the NTP-binding helicase domain, and two small polypetides (12-13 103 and 7 103) with membrane-binding functions.
None reported.
None reported.
Genome Organization and Replication
ASPV and RSPaV genomes contain 5 ORFs each (Fig. 2). The 5 region of ASPV initiates with a non coding sequence of 33 nts, ORF1 codes for the replication-related proteins with conserved motifs of the “alpha-like” supergroup of positive-strand ssRNA viruses (i.e., methyltrasferase and RdRp); ORF2, ORF3, and ORF4 constitute the triple gene block thought to be involved in cell-to-cell spread of the virus; ORF5 is the CP cistron. A noncoding sequence of 135 nts followed by a poly(A) tail terminates the sequence. RSPaV possesses an identical genome structure, expressing products of similar size as those of ASPV, except for the CP which is smaller (28 103 viz. 44 103). The noncoding regions at the 5 and 3 ends encompass 61 and 176 nts, respectively. The 5-end of CGRMV is capped and the viral genome sequence contains two additional ORFs (ORF2a and ORF4a) nested in ORF2 and ORF5, respectively, which potentially encode polypeptides 14 103 and 18 103 in size, for which no similarity was found with other proteins in databases. ASPV virions accumulate in the cytoplasm where multiplication is likely to occur with a strategy comparable to that of potexviruses, based on direct expression of the 5-proximal ORF, and expression of downstream ORFs through subgenomic RNAs. Multiple dsRNAs are found in infected hosts. Tissue extracts yield a prominent band of about 10 kbp and at least four bands with lower molecular weight for ASPV, two bands with a Mr of 5.3 and 4.4 106 for RSPaV, and one major band with a Mr of 4.9-5.0 106 for CGRMV.
Antisera to ASPV that can be used in immunocapture PCR and ELISA, have been raised from purified virions of chimeric fusion CPs expressed in Escherichia coli. A CGRMV particle-decorating antiserum was also produced from fusion proteins. There is no recognized serological relationships among virus species.
The natural host range of individual species is restricted to a single (RSPaV) or a few hosts (ASPV, CGRMV). ASPV infects primarily pome fruits, causing diseases of apple (topworking disease) when grafted on susceptible rootstocks, and of pear (vein yellows and necrotic spot). RSPaV is a grapevine pathogen. Stone fruits (sweet, sour and flowering cherries, peach, and apricot) are the natural hosts of CGRMV. The experimental host range is restricted.
No vector is known for any of the viruses but all are transmitted by grafting and persist in the host propagative material. ASPV is mechanically transmissible, with some difficulty, to Nicotiana occidentalis and its subspecies obliqua CGRMV was transmitted by sap inoculation from cherry to cherry but not to a range of herbaceous hosts.
All species have a rather 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. Massive accumulations of virus-like particles were also observed in mesophyll cells of CGRMV-infected Kwazan flowering cherry.
List of Species Demarcation Criteria in the Genus
The criteria demarcating species in the genus are:
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Natural host range, |
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Mechanical transmissibility, |
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Serological specificity (all known species are serologically unrelated), |
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Coat protein size, |
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Amino acid sequences of any of the genes differing by more than 10%. |
Official virus species names are in italics. Tentative virus species names, alternative names ( ), strains or serotypes are not italicized. Virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ) are:
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Apple stem pitting virus |
[D21829] |
(ASPV) |
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(Pear vein yellows virus) |
[D21828] |
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Rupestris stem pitting-associated virus |
(RSPaV) |
Tentative Species in the Genus
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Cherry green ring mottle virus |
[AF017780] |
(CGRMV) |
Phylogenetic Relationships within the Genus
Not available.
Virions have a particle morphology similar to that of viral species in the genera Closterovirus, Crinivirus, Trichovirus, Vitivirus, Capillovirus and Allexivirus. The structure and organization of the viral genome closely resembles that of the genera Potexvirus, Carlavirus and Allexivirus in the number and order of genes, but ORF1 and, limitedly to ASPV, the CP cistron are significantly larger. Replication-related proteins encoded by ORF1 contain signature sequences homologous to those found in other members of the “alpha-like” supergroup of ssRNA positive-sense viruses, especially those of the genera Potexvirus, Carlavirus and Allexivirus. Comparable similarities are found between the expression products of the triple gene block which is also present in the above genera. Coat proteins of all species share distinct homologies with those of potexviruses and carlaviruses, the closest being potexviruses as shown by phylogenetic analysis of the CP sequences of the genera.
Fovea: from fovea, Latin for pit, hole, the name of the symptom induced by the type species.
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