Viroid

Viroids are the smallest infectious agents and consist of an annularly closed, single-stranded ribonucleic acid ( RNA). Unlike viruses, viroids have no additional proteins or lipids in the form of a shell or a capsid. Viroids can only reproduce inside living cells ( obligate intracellular parasites), which is why they also form together with the viruses, and prions virusoids the group of sub-cellular pathogens. The RNA of viroids is 241-401 nucleotides long. Typically, this is transcribed from genomic RNA during replication in the cell no messenger RNA and thus does not synthesize viroid -specific proteins. The viroid RNA has its own catalytic activity, among others, in the form of a ribozyme. The mechanism of RNA replication and interaction with cellular factors is an interesting model to study the functionality of RNA in the cell. These mechanisms of viroids are considered to be a molecular fossil from an early stage of chemical evolution.

Infection with viroids have so far been found only in vascular plants. The infections affect many different crops, with the resulting disease, depending on environmental conditions and host-pathogen relationship may either not or only mild break out or cause serious damage and death of plants. The economic damage caused by viroids affect primarily potato plants, tomatoes, citrus fruits, grapes and ornamentals.

Discovery

The first disease caused by the spindle tuber viroid addiction has been studied in the potato plant. Their infectious nature was recognized in 1923 by Eugene S. Schultz and Donald Folsom, however, the specific nature of the pathogen remained unknown at first and he was assigned to the plant viruses. The operating in Maryland on Agricultural Research Service plant pathologist Theodor O. Diener succeeded in 1971 with the characterization of the then Potato Spindle Tuber Virus said plant virus ( later Potato Spindle Tuber Viroid ) the first evidence of infectivity of RNA with no protein component. This RNA is able to replicate within a plant cell itself. He suggested the name viroid - ie virus -like - for this group of pathogens before. Heinz Ludwig Sänger could prove in 1976 at the Institute of Virology, Justus -Liebig- University Giessen, the structure of viroids as covalently closed, single-stranded RNA rings with specific base pairs within the RNA strand. He showed also helically wound sections within the RNA ring with which the particular energetic stability of the RNA was explainable.

Genome structure and

The RNA of viroids contains many complementary regions, thereby form double-stranded, linear structures than about 50 nm long rod-like structures can be observed in the electron microscope.

Unlike viruses, viroids do not encode proteins. Therefore, they are dependent on their replication and their transport exclusively on enzymes of the host plant. This differs fundamentally from viroids satellite viruses that are dependent on their replication on helper viruses. The exact mechanism by which acts in plants to pathogenic viroid RNA is not known. Various models have been proposed (e., RNA silencing ).

Biological Significance

Viroids occur only as pathogens of plants ( plant pathogen ). In animals, viroids have not yet been discovered; most have so far been identified in crops. A typical example is the potato spindle tuber viroid Potato spindle tuber viroid ( PSTVd ​​Abbr ) which affects potatoes, tomatoes, and many other plant species and wreaks huge economic damage.

System

On the basis of sequence comparisons already -characterized viroid RNA ( currently 29 species and a variety of variants) and their different catalytic and structural properties are divided into two viroids virus families and eight genera.

  • Family Pospiviroidae
  • Genus Pospiviroid
  • Genus Cocadviroid
  • Genus Hostuviroid
  • Genus Apscaviroid
  • Genus Coleviroid
  • Family Avsunviroidae
  • Genus Avsunviroid
  • Genus Pelamoviroid
  • Genus Elaviviroid

Swell

  • David M. Knipe, Peter M. Howley ( ed. -in- chief): Fields' Virology. 5th edition, ISBN 0-7817-6060-7 Philadelphia 2007
  • CM Fauquet, MA Mayo et al.: Eighth Report of the International Committee on Taxonomy of Viruses. London, San Diego, 2005 ISBN 0-12-249951-4
  • R. Flores, R. A. Owens: viroid. In: Brian WJ Mahy and Marc H. van Regenmortel (eds. ): Encyclopedia of Virology, 3rd Edition, San Diego 2008, Volume 5, pp. 332-342 ISBN 978-0-12-373935-3
  • B. Ding, A. Itaya: Viroid: a useful model for studying the basic principles of infection and RNA biology. Mol Plant Microbe Interact. (2007 ) 20 ( 1): pp. 7-20 (Review) PMID 17,249,418 ( full text )
  • EM Tsagris, AE Martínez de Alba, M. Gozmanova, K. Kalantidis: viroid. Cell Microbiol. (2008 ) 10 ( 11): pp. 2168-2179 (Review) PMID 18,764,915 ( full text )
Double helix (disambiguation) Science (journal) Nucleic Acids Research
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