Pospiviroidae


The Pospiviroidae are a incertae sedis family of ssRNA viroids with 5 genera and 39 species, including the first viroid to be discovered, PSTVd, which is part of genus Pospiviroid. Their secondary structure is key to their biological activity. The classification of this family is based on differences in the conserved central region sequence. Pospiviroidae replication occurs in an asymmetric fashion via host cell RNA polymerase, RNase, and RNA ligase. Its hosts are plants, specifically dicotyledons and some monocotyledons. The severity of the infection can vary from no effect to devastating and widespread damage to a population. This can also depend on the virus-host combination.

Genome

Members of the family Pospiviroidae have circular ssRNA of 246–375 nt. They assume rod-like or quasi-rod-like conformations containing a central conserved region and a terminal conserved hairpin or a terminal conserved region. The genome of viroids does not encode any proteins.

Replication

Its replication is nuclear and mediated by DNA-dependent RNA polymerase II, which is redirected to use RNA templates through an asymmetric RNA–RNA rolling-circle mechanism. polarity circRNA molecules are repeatedly transcribed into oligomeric complementary RNAs. Such intermediates serve as templates for generating oligomeric RNAs that are cleaved by a host enzyme of the RNase III class. The termini of the resulting linear monomers are ligated by the host DNA ligase 1 to generate the mature circular viroid RNA.

Taxonomy

Cocadviroid
Coleviroid
  • Coleus blumei viroid 1
  • Coleus blumei viroid 2
  • Coleus blumei viroid 3
  • Coleviroid cbvd-5
  • Coleviroid cbvd-6
Hostuviroid
Pospiviroid