|- |(unranked)||Viroid Pospiviroidae
Avsunviroidae Viroids are infectious agents that consist of single-stranded RNA. They are much smaller and simpler than viruses and lack the protein cover that is typical for viruses. Viroids use higher plants (such as potatoes, tomatoes and cucumbers) to reproduce, inserting themselves into the nucleus of a plant cell to be replicated there. Viroids are usually transmitted by seed or pollen. Infected plants can show distorted growth. The first viroid to be identified was the Potato spindle tuber viroid (PSTV).

Primary and secondary structure of the PSTV viroid:

  1   CGGAACUAAA CUCGUGGUUC CUGUGGUUCA CACCUGACCU CCUGAGCAGA AAAGAAAAAA
 61   GAAGGCGGCU CGGAGGAGCG CUUCAGGGAU CCCCGGGGAA ACCUGGAGCG AACUGGCAAA
121   AAAGGACGGU GGGGAGUGCC CAGCGGCCGA CAGGAGUAAU UCCCGCCGAA ACAGGGUUUU
181   CACCCUUCCU UUCUUCGGGU GUCCUUCCUC GCGCCCGCAG GACCACCCCU CGCCCCCUUU
241   GCGCUGUCGC UUCGGCUACU ACCCGGUGGA AACAACUGAA GCUCCCGAGA ACCGCUUUUU
301   CUCUAUCUUA CUUGCUUCGG GGCGAGGGUG UUUAGCCCUU GGAACCGCAG UUGGUUCCU

Some 33 species have been identified.

Taxonomy

• Family Pospiviroidae
  • Genus Pospiviroid; type species: Potato spindle tuber viroid
  • Genus Hostuviroid ; type species: Hop stunt viroid
  • Genus Cocadviroid ; type species: Coconut cadang-cadang viroid
  • Genus Apscaviroid ; type species: Apple scar skin viroid
  • Genus Coleviroid ; type species: Coleus blumei viroid 1
• Family Avsunviroidae
  • Genus Avsunviroid ; type species: Avocado sunblotch viroid
  • Genus Pelamoviroid ; type species: Peach latent mosaic viroid

See also

• Virus
• Virusoid
• Virus classification