No trans-replication of genomes by Rep proteins,
Complete genome sequence identity less than 75%,
Antigen differences,
Different vector species,
Differences in host range/pathogenicity.
|
Type Species |
(MSV) |
The genomes of mastreviruses consist of a single component of circular ssDNA, 2.6-2.8 kb in size. A small complementary sense primer-like oligonucleotide annealed to the genomic DNA within the small intergenic region, has been found for five species; Chloris striate mosaic virus (CSMV), Digitaria streak virus (DSV), MSV, Tobacco yellow dwarf virus (TYDV), and Wheat dwarf virus (WDV).
The genome codes for three (possibly four) proteins: these are the CP (V2 ORF), which encapsidates the genome and possibly acts as a nuclear shuttle protein; MP (V1 ORF), which acts in cell-to-cell movement; replication-associated protein (Rep, C1/C2 ORFs), which initiates viral replication, and possibly also RepA (C1 ORF), which may be involved in replication. The CP apparently also regulates ds to ssDNA conversion.
Genome Organization and Replication
The entire nucleotide sequences of infectious genomic clones of nine species (Bean yellow dwarf virus (BeYDV), CSMV, DSV, MSV, Miscanthus streak virus (MiSV), Panicum streak virus (PanSV), Sugarcane streak virus (SSV), TYDV and WDV have been determined. Mastrevirus genomes contain four ORFs, two each on the viral and complementary strands. ORFs C1 and C2 apparently comprise two exons (RepA and RepB) of one replication-associated (Rep) gene. For all species except MSV, RepB lacks a methionine start codon. MSV and grass-infecting relatives have a putative intron in the MP gene (V1 ORF); all mastreviruses have an intron in the Rep gene (Fig. 2).
Serological analyses indicate that grass-infecting geminiviruses from the same continent constitute distinct groupings: there is an African streak virus group (MSV, PanSV, SSV), an Australasian striate mosaic virus group (CSMV, Bromus striate mosaic virus (BrSMV), Digitaria striate mosaic virus (DiSMV), Paspalum striate mosaic virus (PSMV)), and the very distinct Asian MiSV and European WDV. Although DSV originates from Vanuatu, it is most closely related to the African mastreviruses. Grass geminiviruses originating from different continents are either unrelated or distantly related. The dicot-infecting mastreviruses (TYDV, BeYDV) are not related to the monocot-infecting viruses.
Mastreviruses have narrow host ranges. With the exception of TYDV and BeYDV (which infect certain Solanaceae and Leguminosae, among others), host ranges of mastreviruses are limited to members of the Poaceae (Graminae).
Mastreviruses are transmitted in nature by leafhoppers (Homoptera: Cicadellidae), in most cases by a single species. Mechanism of transmission is persistent (circulative, non-propagative). Mastreviruses are normally not transmissible by mechanical inoculation; however, MSV has been transmitted via the vascular puncture technique on maize seeds. Most members have been transmitted experimentally to plants by Agrobacterium-mediated transfer from partially dimeric genomic clones (BeYDV, CSMV, DSV, MSV, MiSV, PanSV, TYDV, WDV).
List of Species Demarcation Criteria in the Genus
The criteria demarcating species in the genus are:
|
No trans-replication of genomes by Rep proteins, |
|
Complete genome sequence identity less than 75%, |
|
Antigen differences, |
|
Different vector species, |
|
Differences in host range/pathogenicity. |
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:
|
Bean yellow dwarf virus |
[Y11023] |
(BeYDV) |
|
Bromus striate mosaic virus |
(BrSMV) | |
|
Chloris striate mosaic virus (221) |
[M20021] |
(CSMV) |
|
Digitaria streak virus |
[M23022] |
(DSV) |
|
Digitaria striate mosaic virus |
(DiSMV) | |
|
Maize streak virus (133) |
[X01089, X01633, AF003952, Y00514, X71954, AF007881] |
(MSV) |
|
Miscanthus streak virus (348) |
[D00800, D01030] |
(MiSV) |
|
Panicum streak virus |
[X60168, L39638] |
(PanSV) |
|
Paspalum striate mosaic virus |
(PSMV) | |
|
Sugarcane streak virus |
[M82918, X86705] |
(SSV) |
|
Tobacco yellow dwarf virus (278) |
[M81103] |
(TYDV) |
|
Wheat dwarf virus |
[X02869, X82104] |
(WDV) |
Tentative Species in the Genus
|
Bajra streak virus |
(BaSV) |
|
|
Chickpea chlorotic dwarf virus |
(CpCDV) |
|
|  |