''Ascoviridae'' is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of double strand DNA viruses that infect primarily

invertebrates Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum ...

, mainly noctuids and spodoptera species. The family contains two genera: ''Ascovirus'' and ''Toursvirus''.

Taxonomy

The family contains the following genera and species: * ''

Ascovirus ''Ascoviridae'' is a Family (biology), family of double strand DNA viruses that infect primarily invertebrates, mainly noctuids and spodoptera species. The family contains two genera: ''Ascovirus'' and ''Toursvirus''. Taxonomy The family contai ...

'' ** ''Ascovirus hvav3a'' ** ''Ascovirus sfav1a'' ** ''Ascovirus tnav2a'' * '' Toursvirus'' ** ''Toursvirus dptv1a''

Genome

The genome is not segmented and contains a single molecule of circular double-stranded

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

. The genome has a

guanine Guanine () (symbol G or Gua) is one of the four main nucleotide bases 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 ...

cytosine Cytosine () (symbol C or Cyt) is one of the four nucleotide bases 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 attac ...

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 cyste ...

, 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

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 ...

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 ubiquitin ...

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 Acyltransferase is a type of transferase enzyme that acts upon acyl In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen ...

and a patatin-like

phospholipase A phospholipase is an enzyme that hydrolyzes phospholipids into fatty acids and other lipophilic substances. There are four major classes, termed A, B, C, and D, which are distinguished by the type of reaction which they catalyze: *Phospholipase ...

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 m ...

is enveloped and measures 130 nm in diameter, and 200-240 nm in length. Virions are

bacilliform Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archaea ...

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 of mathematics (projective geometry, technical drawing, etc.), it is given a more precise definition, which may inc ...

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

Lepidoptera Lepidoptera ( ) or lepidopterans is an order (biology), order of winged insects which includes butterflies and moths. About 180,000 species of the Lepidoptera have been described, representing 10% of the total described species of living organ ...

'', 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 ...

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, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph ce ...

, 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 ...

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 genera ...

'') 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 ''Ichnovirus'' contained ...

es (family ''

Polydnaviridae ''Polydnaviriformidae'' ( PDV) is a family of insect viriforms; members are known as polydnaviruses. There are two genera in the family: '' Bracoform'' and '' Ichnoviriform''. Polydnaviruses form a symbiotic relationship with parasitoid wasps. ...

''), 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