Notes on Family: Closteroviridae
This family is characterised by its very long (up to 2000 nm) and very flexuous particles. Its members have the largest genomes of all positive sense RNA plant viruses (up to 20 kb) and duplicate coat protein genes. Infected plant cells contain massive particle aggregates, often organized into banded inclusions.
Virions filamentous, not enveloped, very flexuous, 950-2000 nm long and 10-13 nm in diameter. There is a distinct virion tail. Symmetry helical, with pitch of 3.4-3.7 nm.
Virions are composed of 5% nucleic acid.
Mono- or bi-partite, linear positive sense ssRNA up to 20 kb in length. There are sequences with potential hairpin structure near the 3'-end. 3' terminus has no poly(A) tract and the 5' terminus probably has a methylated nucleotide cap. The genome has up to about 12 open reading frames, including two coat proteins towards (but not at) the 3'-terminus. The minor coat protein occurs only in the virion tail.
Genera in the Family
- Ampelovirus (monopartite genome; mealybug-transmitted; major coat protein upstream of diverged minor, coat protein)
- Closterovirus (monopartite genome; mostly aphid-transmitted; major coat protein downstream from diverged, minor, coat protein)
- Crinivirus (bipartite genome; whitefly-transmitted)