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GENUS
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Begomovirus
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Type Species
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Bean golden mosaic virus-Puerto Rico
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(BGMV-PR)
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http://www.danforthcenter.org/iltab/geminiviridae/description/genbego.htm
DISTINGUISHING
FEATURES
NUCLEIC ACID
The genome of most
begomoviruses of the Old World and all "New World" begomoviruses
consist of two components, each 2.5-2.8 kb in size; however, there are
begomoviruses with only a single ssDNA component (eg: AYVV, some TYLCVs,
ToLCV): these are all "Old World" or from
Eurasia/Africa/Australasia. A satellite circular ssDNA has recently
been found associated with a single-component begomovirus: this is
encapsidated by the viral CP and replicated by viral Rep, and contains the
TAATATTAC nonanucleotide common to all Geminiviridae.
PROTEINS
Characterised protein
products are the coat protein (CP, AV1 ORF), responsible for encapsidation
and which may be involved in movement; the replication associated protein
(Rep, AC1 ORF); the transcriptional activator protein (TrAP, AC2 ORF); the
replication enhancer protein (REn, AC3 ORF); the product of the AC4 ORF,
which is a major determinant of symptom expression; the cell-to-cell
movement protein (MP, BC1 ORF), and the nuclear shuttle protein (NSP, BV1
ORF).
GENOME ORGANIZATION
AND REPLICATION
The
autonomously-replicating component (whole genome or DNA A) encodes five to
six genes (one or two on the virion and four on the complementary strand)
whereas the dependent component (DNA B, if present) encodes two genes (one
on each strand). The two genomic components (if present) share an
approximately 200 bp block of sequence (encompassing the conserved
TAATATTAC sequence) within the intergenic region (IR) which is then termed
the common region (CR). The complete genomes of more than 40 distinct
begomoviruses have been sequenced.
Figure 4: Typical
genomic organization of begomoviruses. ORFs are denoted as either
being encoded on the virion (V) or complementary (C) strand, preceded by
component designation if bipartite. The coat protein is encoded by the
CP gene (ORF AV1). The position of the stemloop containing the
conserved TAATATTAC sequence is shown. The common region (CR) of
sequence shared between the two genomic components is shown (grey boxes). TrAP
= transcriptional activator protein; Rep = replication associated protein,
REn = replication enhancer, MP = movement protein, NS = nuclear shuttle
protein. AV2 ORF not present in New World begomoviruses.
ANTIGENIC PROPERTIES
Serological tests show
all begomoviruses to be relatively closely related. The use of
monoclonal antisera has shown that begomoviruses may be grouped
geographically based on shared epitopes.
BIOLOGICAL PROPERTIES
HOST RANGE
Individual begomoviruses
generally have narrow host ranges amongst dicotyledonous plants.
TRANSMISSION
Transmitted exclusively
in nature by the whitefly Bemisia tabaci (Genn.), although some groups
distinguish the "B" or silverleaf biotype as Bemisia
argentifolii. Some species are transmissible by mechanical inoculation. Experimentally
some species have been transmitted by either Agrobacterium-mediated
transfer of cloned genome components, or biolistically, either using
recombinant DNA methods (eg: AbMV, ACMV, AYVV, BDMV, BGMV, PHV, PYMV, SLCV,
TGMV, TMoV, ToLCV, TYLCV), or by use of total nucleic acid extracts from
infected plants.
LIST OF SPECIES
DEMARCATION CRITERIA IN THE GENUS
The list of species
demarcation criteria in the genus Begomovirus are:
- Different numbers of genome components,
- Different organization of genes in the genome,
- No trans-complementation of gene products,
- No pseudorecombination between components,
- Complete genome A sequence identity < 90%,
- Coat protein sequence identity < 90%,
- Virions react differently with key antibodies,
- Different tissue tropism,
- Host range different in key species.
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