Family of viruses
Tombusviridae
is a family of single-stranded
positive sense
RNA
plant
viruses
. There are three subfamilies, 17 genera, and 95 species in this family.
[1]
[2]
The name is derived from
Tomato bushy stunt virus
(TBSV).
[3]
Genome
[
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]
All viruses in the family have a non-segmented (monopartite) linear
genome
, with the exception of Dianthoviruses, whose genome is bipartite.
[4]
The genome is approximately 4.6?4.8kb in length, lacks a
5' cap
and a poly(A) tail, and it encodes 4?6
ORFs
. The polymerase encodes an
amber stop codon
which is the site of a readthrough event within ORF1, producing two products necessary for replication. There is no
helicase
encoded by the virus.
[5]
Structure
[
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]
The RNA is encapsulated in an
icosahedral
(T=3)
capsid
, composed of 180 units of a single coat protein 27?42K in size; the
virion
measures 28?35 nm in diameter, and it is not enveloped.
[1]
[6]
Life cycle
[
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]
Viral replication is cytoplasmic, and is lysogenic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription, using the premature termination model of subgenomic RNA transcription is the method of transcription. Translation takes place by leaky scanning, ?1 ribosomal frameshifting, viral initiation, and suppression of termination. The virus exits the host cell by tubule-guided viral movement. Plants serve as the natural host. Transmission routes are mechanical, seed borne, and contact.
[1]
[7]
Viruses in this family are primarily soil-borne, some transmitted by fungal species of the order
Chytridiales
, others by no known vector. Virions may spread by water, root growth into infected soil, contact between plants, pollen, or seed, depending on the virus species. These viruses may be successfully transmitted by
grafting
or mechanical inoculation, and both the virion and the genetic material alone are infective.
[6]
Replication
[
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]
Members of
Tombusviridae
replicate
in the cytoplasm, by use of negative strand templates. The replication process leaves a surplus of positive
sense
(+)RNA strands, and it is thought that not only does the viral RNA act as a template for replication, but is also able to manipulate and regulate
RNA synthesis
.
[5]
The level of RNA synthesis has been shown to be affected by the
cis-acting
properties of certain elements on the RNA (such as
RNA1 and 2
[8]
[9]
), which include core promoter sequences which regulate the site of initiation for the complementary RNA strand synthesis. This mechanism is thought to be recognised by RNA-dependent
RNA polymerase
, found encoded within the genome.
[5]
[7]
[10]
Viruses in
Tombusviridae
have been found to co-opt
GAPDH
, a host metabolic enzyme, for use in the replication center. GAPDH may bind to the (?)RNA strand and keep it in the replicase complex, allowing (+)RNA strands synthesized from it to be exported and accumulate in the host cell. Downregulation of GAPDH reduced viral RNA accumulation, and eliminated the surplus of (+)RNA copies.
[11]
Notes
[
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]
Research has shown that infection of plants from tombusviruses contain defective interfering RNAs that are born directly from the viruses RNA genome, and no host genome. Viral DI RNAs with their small size and cis-acting elements are good templates both
in vivo
and
in vitro
on which to study RNA replication.
[12]
[13]
[14]
Sub-genomic RNA is used in the synthesis of some proteins; they are generated by premature termination of (?)strand synthesis. sgRNAs and sgRNA negative-sense templates are found in infected cells.
[6]
Taxonomy
[
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]
The family contains the following subfamilies and genera (-
virinae
denotes subfamily and -
virus
denotes genus):
[2]
Lastly, one genus is unassigned to a subfamily:
Luteovirus
.
[2]
References
[
edit
]
- ^
a
b
c
"Viral Zone"
. ExPASy
. Retrieved
15 June
2015
.
- ^
a
b
c
"Virus Taxonomy: 2020 Release"
. International Committee on Taxonomy of Viruses (ICTV). March 2021
. Retrieved
16 May
2021
.
- ^
Habili, N. and Symons, R. H. (1989).
Evolutionary relationship between luteoviruses and other RNA plant viruses based on sequence motifs in their putative RNA polymerases and nucleic acid helicases.
Nucleic Acids Research
17
:23, 9543?55
- ^
Wiley InterScience Encyclopedia of Life Sciences: Tombusviridae
- ^
a
b
c
ICTV
:
Family - Tombusviridae
, in: Virus Taxonomy. Ninth Report of the International Committee on Taxonomy of Viruses 2012, pp 1111-1138, 23 November 2011,
doi:10.1016/B978-0-12-384684-6.00096-3
- ^
a
b
c
ICTVdB?The Universal Virus Database, version 3
00.074.
Tombusviridae
- ^
a
b
Beth L. Nicholson, Pui Kei K. Lee, K. A. White:
Internal RNA replication elements are prevalent in
Tombusviridae
, in: Front. Microbiol., 06 August 2012,
doi:10.3389/fmicb.2012.00279
- ^
Lommel SA, Weston-Fina M, Xiong Z, Lomonossoff GP (September 1988).
"The nucleotide sequence and gene organization of red clover necrotic mosaic virus RNA-2"
.
Nucleic Acids Res
.
16
(17): 8587?602.
doi
:
10.1093/nar/16.17.8587
.
PMC
338578
.
PMID
3047682
.
- ^
Mizumoto H, Tatsuta M, Kaido M, Mise K, Okuno T (November 2003).
"Cap-independent translational enhancement by the 3' untranslated region of red clover necrotic mosaic virus RNA1"
.
J. Virol
.
77
(22): 12113?21.
doi
:
10.1128/JVI.77.22.12113-12121.2003
.
PMC
254280
.
PMID
14581548
.
- ^
K. Andrew White, Peter D. Nagy:
Advances in the Molecular Biology of Tombusviruses: Gene Expression, Genome Replication, and Recombination
, in: Progress in Nucleic Acid Research and Molecular Biology, Vol. 78, 2004, pp. 187-226,
doi:10.1016/S0079-6603(04)78005-8
- ^
Wang, R. and Nagy, P. (2008) Tomato bushy stunt virus Co-Opts the RNA-Binding Function of a Host Metabolic Enzyme for Viral Genomic RNA Synthesis.
Cell Host & Microbe
3
:3 178?187
- ^
NCBI:
Defective interfering RNA-4 of tomato bushy stunt virus
(TBSV-P DI-4) and
Defective interfering RNA-5 of tomato bushy stunt virus
(TBSV-P DI-5)
- ^
Yamamura, Yoshimi; Scholthof, Herman B. (1 September 2005). "Tomato bushy stunt virus: a resilient model system to study virus-plant interactions".
Molecular Plant Pathology
.
6
(5): 491?502.
doi
:
10.1111/j.1364-3703.2005.00301.x
.
PMID
20565674
.
- ^
Scholthof, Karen-Beth G.; Scholthof, Herman B.; Jackson, Andrew O. (1 August 1995).
"The Effect of Defective Interfering RNAs on the Accumulation of Tomato Bushy Stunt Virus Proteins and Implications for Disease Attenuation"
.
Virology
.
211
(1): 324?328.
doi
:
10.1006/viro.1995.1410
.
PMID
7645230
.
External links
[
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]