''Ascoviridae'' is a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

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 chordate ...

, 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 ''Ascoviridae'' is a family of double strand DNA viruses that infect primarily invertebrates, mainly noctuids and spodoptera species; it contains two genera, ''Ascovirus'', which contains three species, and ''Toursvirus'' with a single species ' ...

'' ** '' Heliothis virescens ascovirus 3a'' ** '' Spodoptera frugiperda ascovirus 1a'' ** '' Trichoplusia ni ascovirus 2a'' * '' Toursvirus'' ** ''Diadromus pulchellus toursvirus''

Genome

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 called ...

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 am ...

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 Caspases (cysteine-aspartic proteases, cysteine aspartases or cysteine-dependent aspartate-directed proteases) are a family of protease enzymes playing essential roles in programmed cell death. They are named caspases due to their specific cystei ...

, 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 cert ...

, several

kinase In biochemistry, a kinase () is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. This process is known as phosphorylation, where the high-energy ATP molecule don ...

s, E3 ubiquitin ligases, a fatty acid elongase, a sphingomyelinase, a phosphate

acyltransferase Acyltransferase is a type of transferase enzyme that acts upon acyl groups. Examples include: * Glyceronephosphate O-acyltransferase * Lecithin-cholesterol acyltransferase *Long-chain-alcohol O-fatty-acyltransferase In enzymology, a long-chain- ...

and a

patatin Patatin is a family of glycoproteins found in potatoes (''Solanum tuberosum'') and is also known as tuberin as it is commonly found within vacuoles of parenchyma tissue in the tuber of the plant. They consist of about 366 amino acids all making up ...

-like phospholipase.

Virology

The virions consist of an envelope, a core, and an internal lipid membrane associated with the inner particle. The virus capsid is enveloped and measures 130 nm in diameter, and 200-240 nm in length. Virions are

bacilliform A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name ''Bacillu ...

ovoid An oval () is a closed curve in a plane which resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or ...

, and allantoid. These viruses infect immature stages of the order ''

Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...

'', 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

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), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features o ...

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, making it milky white, a characteristic of this disease. The circulation of virions and vesicles in the blood facilitates mechanical transmission by parasitic wasps.

Evolution

Ascoviruses evolved from iridoviruses (family '' Iridoviridae'') that also attack lepidopteran larvae. Furthermore, ascoviruses have been suggested as the evolutionary source of ichnoviruses (family '' Polydnaviridae''), 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