The Pospiviroidae are a ''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'' family of ssRNA

viroid Viroids are small single-stranded, circular RNAs that are infectious pathogens. Unlike viruses, they have no protein coating. All known viroids are inhabitants of angiosperms (flowering plants), and most cause diseases, whose respective eco ...

s with 5

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

and 39

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, including the first viroid to be discovered, PSTVd, which is part of genus Pospiviroid. Their secondary structure is key to their

biological activity In pharmacology, biological activity or pharmacological activity describes the beneficial or adverse effects of a drug on living matter. When a drug is a complex chemical mixture, this activity is exerted by the substance's active ingredient or ...

. 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 In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template. Using the e ...

RNase Ribonuclease (commonly abbreviated RNase) is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within the ...

, and RNA ligase. Its hosts are

plants Plants are the eukaryotes that form the kingdom Plantae; they are predominantly photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with cyanobacteria to produce sugars f ...

, specifically

dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, ...

s and some

monocotyledon Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but with various ranks ...

s. 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 (CCR) and a terminal conserved hairpin (TCH) or a terminal conserved region (TCR). 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 (by convention the most abundant strand ''in vivo'') are repeatedly transcribed into

oligomeric In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomer, monomers.Quote: ''Oligomer molecule: A molecule of intermediate ...

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 A monomer ( ; ''wikt:mono-, mono-'', "one" + ''wikt:-mer, -mer'', "part") is a molecule that can chemical reaction, react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called ...

are ligated by the host DNA ligase 1 to generate the mature circular viroid RNA.

Taxonomy

Apscaviroid * Apple dimple fruit viroid * Apple scar skin viroid * Apscaviroid aclsvd * Apscaviroid cvd-VII * Apscaviroid dvd * Apscaviroid glvd * Apscaviroid lvd * Apscaviroid plvd-I * Apscaviroid pvd * Apscaviroid pvd-2 * Australian grapevine viroid * Citrus bent leaf viroid * Citrus dwarfing viroid * Citrus viroid V * Citrus viroid VI * Grapevine yellow speckle viroid 1 * Grapevine yellow speckle viroid 2 * Pear blister canker viroid Cocadviroid * Citrus bark cracking viroid * Coconut cadang-cadang viroid * Coconut tinangaja viroid * Hop latent viroid

Coleviroid 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 activ ...

* Coleus blumei viroid 1 * Coleus blumei viroid 2 * Coleus blumei viroid 3 * Coleviroid cbvd-5 * Coleviroid cbvd-6 Hostuviroid * Dahlia latent viroid * Hop stunt viroid Pospiviroid * Chrysanthemum stunt viroid * Citrus exocortis viroid * Columnea latent viroid * Iresine viroid 1 * Pepper chat fruit viroid * Pospiviroid plvd *

Potato spindle tuber viroid The potato spindle tuber viroid (PSTVd, ''Pospiviroid fusituberis'') was the first viroid to be identified.

* Tomato apical stunt viroid * Tomato chlorotic dwarf viroid * Tomato planta macho viroid

References

External links

ICTV Report: ''Pospiviroidae''
– extensive information on pospiviroidae and viroids. Viroids {{virus-stub