Begomovirus
Encyclopedia
The genus
Begomovirus contains more than 200 species and belongs to the taxonomic family Geminiviridae
. They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a considerable amount of economic damage to many important crops such as tomato
es, bean
s, squash, cassava
and cotton
.
. Many begomoviruses have a bipartite genome
:, this means that the genome is segmented into two segments (referred to as DNA A and DNA B) that are packaged into separate particles. Both segments are generally required for successful symptomatic infection in a host cell but DNA B is dependent for its replication upon DNA A, which can in some begomoviruses apparently cause normal infections on its own.
The DNA A segment typically encodes five to six proteins including replication protein Rep, coat protein and transport and/or regulatory proteins. This component is homologous to the genomes of all other geminiviruses. The proteins endcoded on it are required for replication (Rep), control of gene expression, overcoming host defenses, encapsidation (coat protein) and insect transmission. The DNA B segment encodes two different movement proteins. These proteins have functions in intra- and intercellular movement in host plants.
The A and B components share little sequence identity with the exception of a ~200 nucleotide sequence with typically >85% identity known as the common region. This region includes an absolutely conserved (among geminiviruses) hairpin structure and repeated sequences (known as 'iterons') that are the recognition sequences for binding of the replication protein (Rep). Within this loop there is a nonanucleotide sequence (TAATATTAC) that acts as the origin (ori) of virion strand DNA replication.
Component exchange (pseudorecombination) occurs in this genus. The usual mechanism of pseudorecombination is by a process known as 'regulon grafting': the A component donates its common region by recombination to the B component being captured. This results in a new dependent interaction between two components.
The proteins in this genus may lie either on the sense strand (positive orientation) or its complement (negative orientation).
More than 133 begomovirus species having monopartite genomes are known: all originate from the Old World. No monopartite begomoviruses native to the New World have yet been identified.
Phylogenetic analysis is based on the A component. B components may be exchanged between species and may result in new species.
Analysis of the genus reveals a number of clades.. The main division is between the Old and New World strains. The Old World strains can be divided into African, Indian, Japanese and other Asian clades with a small number of strains grouping outside these. The New World strains divide into Central and Southern America strains.
Along with these main groupings are a number of smaller clades. One group infecting a range of legumes originating from India and Southeast Asia (informally 'Legumovirus') and a set of viruses isolated from Ipomoea
species originating from America, Asia and Europe (informally 'Sweepovirus') appear to be basal to all the other species. Two species isolated from Corchorus
from Vietnam (informally 'Corchovirus') somewhat unexpectedly group with the New World species.
this disease in tomato is endemic and causes an estimated yield loss of 50–60%. PYMV disease is also an economical problem in the Caribbean
. The type species Bean golden yellow mosaic virus (BGYMV) also belongs to the Begomovirus genus. It causes a serious disease in bean species within Central America, the Caribbean and southern Florida
.
MicrobiologyBytes: Plant Viruses
Proposed Strategies for Begomovirus Disease Management in Tomato in Trinidad
Bean golden yellow mosaic virus
ViralZone: Begomovirus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Begomovirus contains more than 200 species and belongs to the taxonomic family Geminiviridae
Geminiviridae
Geminiviruses are plant viruses which have single-stranded circular DNA genomes encoding genes that diverge in both directions from a virion strand origin of replication . According to the Baltimore classification they are considered class II viruses...
. They are plant viruses that as a group have a very wide host range, infecting dicotyledonous plants. Worldwide they are responsible for a considerable amount of economic damage to many important crops such as tomato
Tomato
The word "tomato" may refer to the plant or the edible, typically red, fruit which it bears. Originating in South America, the tomato was spread around the world following the Spanish colonization of the Americas, and its many varieties are now widely grown, often in greenhouses in cooler...
es, bean
Bean
Bean is a common name for large plant seeds of several genera of the family Fabaceae used for human food or animal feed....
s, squash, cassava
Cassava
Cassava , also called yuca or manioc, a woody shrub of the Euphorbiaceae native to South America, is extensively cultivated as an annual crop in tropical and subtropical regions for its edible starchy tuberous root, a major source of carbohydrates...
and cotton
Cotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
.
Morphology
Virus particles are non-enveloped. The nucleocaspid is 38 nanometers (nm) long and 15-22 nm in diameter. While particles have basic icosaherdal symmetry, they consist of two incomplete icosahedra - missing one vertex - joined together. There are 22 capsomeres per nucleocapsid.Genome
Single stranded closed circular DNADNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
. Many begomoviruses have a bipartite genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
:, this means that the genome is segmented into two segments (referred to as DNA A and DNA B) that are packaged into separate particles. Both segments are generally required for successful symptomatic infection in a host cell but DNA B is dependent for its replication upon DNA A, which can in some begomoviruses apparently cause normal infections on its own.
The DNA A segment typically encodes five to six proteins including replication protein Rep, coat protein and transport and/or regulatory proteins. This component is homologous to the genomes of all other geminiviruses. The proteins endcoded on it are required for replication (Rep), control of gene expression, overcoming host defenses, encapsidation (coat protein) and insect transmission. The DNA B segment encodes two different movement proteins. These proteins have functions in intra- and intercellular movement in host plants.
The A and B components share little sequence identity with the exception of a ~200 nucleotide sequence with typically >85% identity known as the common region. This region includes an absolutely conserved (among geminiviruses) hairpin structure and repeated sequences (known as 'iterons') that are the recognition sequences for binding of the replication protein (Rep). Within this loop there is a nonanucleotide sequence (TAATATTAC) that acts as the origin (ori) of virion strand DNA replication.
Component exchange (pseudorecombination) occurs in this genus. The usual mechanism of pseudorecombination is by a process known as 'regulon grafting': the A component donates its common region by recombination to the B component being captured. This results in a new dependent interaction between two components.
The proteins in this genus may lie either on the sense strand (positive orientation) or its complement (negative orientation).
Genes
- Segment A
-
- V1 (R1) - positive orientation: Coat protein - 29.7 kiloDaltonAtomic mass unitThe unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
s (kDa) - V2 - positive orientation: Movement protein (precoat ORF) - 12.8 kDa
- C1 (L1) - negative orientation: Replication initiation protein (Rep) - 40.2 kDa
- C2: (L2) - negative orientation: Transciption activator protein (TrAP) - 19.6 kDa
- C3: (L3) - negative orientation: Replication enhancer - 15.6 kDa
- C4: - negative orientation: May determine symptom expression - 12.0 kDa
- V1 (R1) - positive orientation: Coat protein - 29.7 kiloDalton
- Segment B
-
- V1 (R1) - positive orientation: Nuclear shuttle protein - 33.1 kDa
- C1 (L1) - negative orientation: Movement protein - 29.6 kDa
Virology
Smaller than unit length virus components - deletion mutants - are common in infections. These are known as defective interfering (di) DNAs due to their capacity to interfere with virus infection. They reduce virus DNA levels and symptom severity.Phylogenetics
The two components of the genome have very distinct molecular evolutionary histories and likely to be under very different evolutionary pressures. The DNA B genome originated as a satellite that was captured by the monopartite progenitor of all extant bipartite begomoviruses and has subsequently evolved to become an essential genome component.More than 133 begomovirus species having monopartite genomes are known: all originate from the Old World. No monopartite begomoviruses native to the New World have yet been identified.
Phylogenetic analysis is based on the A component. B components may be exchanged between species and may result in new species.
Analysis of the genus reveals a number of clades.. The main division is between the Old and New World strains. The Old World strains can be divided into African, Indian, Japanese and other Asian clades with a small number of strains grouping outside these. The New World strains divide into Central and Southern America strains.
Along with these main groupings are a number of smaller clades. One group infecting a range of legumes originating from India and Southeast Asia (informally 'Legumovirus') and a set of viruses isolated from Ipomoea
Ipomoea
Ipomoea is the largest genus in the flowering plant family Convolvulaceae, with over 500 species. Most of these are called "morning glories", but this can refer to related genera also. Those formerly separated in Calonyction are called "moonflowers"...
species originating from America, Asia and Europe (informally 'Sweepovirus') appear to be basal to all the other species. Two species isolated from Corchorus
Corchorus
Corchorus is a genus of about 40-100 species of flowering plants in the family Malvaceae, native to tropical and subtropical regions throughout the world....
from Vietnam (informally 'Corchovirus') somewhat unexpectedly group with the New World species.
Transmission
The virus is obligately transmitted by an insect vector, which can be the whitefly Bemisia tabaci or can be other whiteflies. This vector allows rapid and efficient propagation of the virus because it is an indiscriminate feeder.Diseases
The type species Potato yellow mosaic virus (PYMV) is a Begomovirus, first identified in the late 1980s, that causes an infection in tomatoes. Disease is manifested in the infected plant as yellow mosaic or mottling, leaf distortion and crinkling and stunting. In TrinidadTrinidad
Trinidad is the larger and more populous of the two major islands and numerous landforms which make up the island nation of Trinidad and Tobago. It is the southernmost island in the Caribbean and lies just off the northeastern coast of Venezuela. With an area of it is also the fifth largest in...
this disease in tomato is endemic and causes an estimated yield loss of 50–60%. PYMV disease is also an economical problem in the Caribbean
Caribbean
The Caribbean is a crescent-shaped group of islands more than 2,000 miles long separating the Gulf of Mexico and the Caribbean Sea, to the west and south, from the Atlantic Ocean, to the east and north...
. The type species Bean golden yellow mosaic virus (BGYMV) also belongs to the Begomovirus genus. It causes a serious disease in bean species within Central America, the Caribbean and southern Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...
.
Additional reading
External links
Notes on Genus: BegomovirusMicrobiologyBytes: Plant Viruses
Proposed Strategies for Begomovirus Disease Management in Tomato in Trinidad
Bean golden yellow mosaic virus
ViralZone: Begomovirus