Notes on Family: Reoviridae

icosahedra

Contents

• Members of this Family
• General Description
• Morphology
• Genome
• Genera in the Family
• All Known Sequences
• Curated Sequences

General Description

This family is characterised by its large, icosahedral particles and its multipartite (9-12 segments), double stranded RNA genome. Plant reoviruses have a number of distinctive features:

1. a highly segmented dsRNA genome, most segments being translated into a single product
2. the capacity to multiply both in plants and their insect vectors
3. many produce growth abnormalities in the plant hosts
4. they are mostly confined to the phloem tissues
5. they are highly host-specific
6. they are related to other viruses affecting humans and animals

Morphology

Virions isometric and icosahedral, not enveloped, 60-80 nm in diameter, with obvious, smooth circular capsomeres on their surface. Capsid has two or three layers. Incomplete virus particles (empty or incompletely assembled capsids) are often present.

Particles contain 15-20 % nucleic acid and 80-85 % protein.

Genomen

Linear, double stranded, RNA in 9-12 segments (depending on genus), encapsidated together in a single type of particle. Total genome 18200-30500 base pairs long. 3' terminus has no poly (A) tract. 5' terminus has a methylated nucleotide cap on the positive strand of each duplex (cap sequence m⁷G(5')ppp(5')GmpNp (type A)) and a phosphorylated terminus on the negative strand.

Genera in the Family

Genera are distinguished by virus particle morphology, the type of host, the number and size of genome segments, the type of vector (in the case of plant viruses) and phylogenetic analyses. The three plant virus genera are marked in bold:

• Subfamily Spinareovirinae (spiked or turreted particles)
  • Aquareovirus (11 segments; viruses of fish and cephalopods)
  • Coltivirus (12 segments migrating in 3 size classes; vertebrate and tick viruses)
  • Cypovirus (10 segments; virions <70nm; insect viruses)
  • Dinovernavirus (9 segments; insect viruses)
  • Fijivirus (10 segments; planthopper vectors)
  • Idnoreovirus (10 segments, non-occluded; insect viruses)
  • Mycoreovirus (11 or 12 segments; infecting fungi)
  • Orthoreovirus (10 segments; virions >70nm; sedimenting at >600S; vertebrate viruses)
  • Oryzavirus (10 segments of different size to Fijivirus; planthopper vectors)
• Subfamily Sedoreovirinae (smooth or non-turreted particles)
  • Cardoreovirus (12 segments; crustacean viruses)
  • Mimoreovirus (11 segments; largest segment >5kb; infecting photosynthetic marine protists)
  • Orbivirus (10 segments; virions >70nm; sedimenting at <600S; vertebrate and arthropod viruses)
  • Phytoreovirus (12 segments; leafhopper vectors)
  • Rotavirus (11 segments; viruses of mammals and birds)
  • Seadornavirus (12 segments evenly spaced in size; vertebrate and mosquito viruses)