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| GENUS |
Mastrevirus |
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| Type Species |
Maize streak virus |
(MSV) |
DISTINGUISHING FEATURES
NUCLEIC ACID
The genome 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
(CSMV, DSV, MSV, TYDV, WDV).
PROTEINS
The genome codes for three (possibly four) proteins: these
are the coat protein (CP, V2 ORF), which encapsidates the genome
and possibly acts as a nuclear shuttle protein; movement 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 (BeYDV, CSMV, DSV, MSV, MiSV, PanSV, SSV,
TYDV, WDV) have been determined. Mastrevirus genomes contain
four open reading frames, 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.
Figure 2: Typical genomic organization of mastreviruses.
Open reading frames are denoted as either being encoded on the
virion (V) or complementary (C) strand, and corresponding enes
are indicated. The positions of the stemloop containing
the conserved TAATATTAC sequence and the encapsidated, complementary
sense primer-like molecule (Z) are shown. Introns are shown
in the RepA/RepB and MP genes. Shaded boxes indicate Large
Intergenic Region (LIR) and Short Intergenic Region (SIR).
ANTIGENIC PROPERTIES
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, BrSMV, DiSMV, PSMV), and the
very distinct Asian MiSV and European WDV. Although DSV
originates from Vanuatu, it is most closely related serologically
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.
BIOLOGICAL PROPERTIES
HOST RANGE
Mastreviruses have narrow host ranges. With the exception
of TYDV and BeYDV (which infect certain Solanaceae and Leguminoseae,
among others), host ranges of mastreviruses are limited to members
of the Poaceae (Graminae).
TRANSMISSION
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 list of species denarcation criteria in the genus Mastrevirus
are:
- No trans-replication of genomes by Rep proteins,
- Complete genome sequence identity <75%,
- Virions react differently with key antibodies,
- Different vector species,
- Host range / pathogenicity different in key species.
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