''Ascoviridae'' is a
family
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...
of double strand DNA viruses that infect primarily
invertebrates
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...
, mainly noctuids and spodoptera species; it contains two genera, ''Ascovirus'', which contains three species, and ''Toursvirus'' with a single species ''Diadromus pulchellus toursvirus''.
Taxonomy
The family contains the following genera and species:
* ''
Ascovirus''
** ''
Heliothis virescens ascovirus 3a''
** ''
Spodoptera frugiperda ascovirus 1a''
** ''
Trichoplusia ni ascovirus 2a''
* ''
Toursvirus''
** ''Diadromus pulchellus toursvirus''
Genome
![Ascoviridae genome](https://upload.wikimedia.org/wikipedia/commons/d/de/Ascoviridae_genome.svg)
The genome is not segmented and contains a single molecule of circular double-stranded
DNA. The genome has a
guanine
Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is c ...
+
cytosine
Cytosine () ( symbol C or Cyt) is one of the four nucleobases found in DNA and RNA, along with adenine, guanine, and thymine (uracil in RNA). It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached (an ...
content of 42-60%.
The genome of Spodoptera frugiperda ascovirus 1a has been sequenced.
It is 156,922 bases in length and encodes 123 putative open reading frames. The G+C ratio is 49.2%. Among the encoded proteins are a
caspase, a
cathepsin B
Cathepsin B belongs to a family of lysosomal cysteine proteases known as the cysteine cathepsins and plays an important role in intracellular proteolysis. In humans, cathepsin B is encoded by the ''CTSB'' gene. Cathepsin B is upregulated in ce ...
, several
kinases,
E3 ubiquitin ligase
A ubiquitin ligase (also called an E3 ubiquitin ligase) is a protein that recruits an E2 ubiquitin-conjugating enzyme that has been loaded with ubiquitin, recognizes a protein substrate, and assists or directly catalyzes the transfer of ubiquiti ...
s, a
fatty acid elongase, a
sphingomyelinase
Sphingomyelin phosphodiesterase (EC 3.1.4.12, also known as neutral sphingomyelinase, sphingomyelinase, or SMase; systematic name sphingomyelin cholinephosphohydrolase) is a hydrolase enzyme that is involved in sphingolipid metabolism reactions. ...
, a phosphate
acyltransferase and a
patatin-like
phospholipase
A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. Acids trigger the release of bound calcium from cellular stores and the consequent increase in free cytosolic Ca2+, an essential step in ...
.
[
]
Virology
The virions consist of an envelope, a core, and an internal lipid membrane associated with the inner particle. The virus capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or ma ...
is enveloped and measures 130 nm in diameter, and 200-240 nm in length. Virions are bacilliform, ovoid, and allantoid.
These viruses infect immature stages of the order '' Lepidoptera'', in which they cause a chronic, fatal disease. They are transmissed by endoparasitic wasps and the host develops a unique cytopathology that resembles apoptosis. Cell infection induces apoptosis and in some species is associated with synthesis of a virus-encoded executioner caspase and several lipid-metabolizing enzymes. After infection the host cell DNA is degraded, the nucleus fragments and the cell then cleaves into large virion-containing vesicles. Synthesis of viral proteins results in the rescue of developing apoptotic bodies that are converted into large vesicle
Vesicle may refer to:
; In cellular biology or chemistry
* Vesicle (biology and chemistry)
In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...
s in which virions accumulate and continue to assemble. In infected larvae, millions of these virion-containing vesicles begin to disperse from infected tissues 48–72 hours after infection into the haemolymph
Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...
, making it milky white, a characteristic of this disease. The circulation of virions and vesicles in the blood facilitates mechanical transmission by parasitic wasp
A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder. ...
s.[
]
Evolution
Ascoviruses evolved from iridoviruses (family ''Iridoviridae
''Iridoviridae'' is a family of viruses with double-stranded DNA genomes. Amphibians, fish, and invertebrates such as arthropods serve as natural hosts. There are currently 22 species in this family, divided among two subfamilies and seven gener ...
'') that also attack lepidopteran larvae. Furthermore, ascoviruses have been suggested as the evolutionary source of ichnovirus
''Ichnovirus'' is a genus of viruses, in the family '' Polydnaviridae''. Parasitoid wasps serve as hosts, and these wasps are themselves parasitoids of Lepidoptera. There are 21 species in this genus.
Taxonomy
The genus contains the following 2 ...
es (family ''Polydnaviridae
A polydnavirus (PDV) is a member of the family ''Polydnaviridae'' of insect viruses. There are two genera in the family: '' Bracovirus'' and ''Ichnovirus''. Polydnaviruses form a symbiotic relationship with parasitoid wasps; (ichnoviruses (IV) ...
''), although other studies have not been able to confirm this link.
References
External links
ICTV Online (10th) Report: Ascoviridae/
*
{{Taxonbar, from=Q6836
Nucleocytoplasmic large DNA viruses
Virus families