Viroids: sequence variability and evolution of pathogenic RNA

Abstract

Viroids as the smallest pathogenic circular single-stranded pathogenic RNAs form populations of quasi-species, whichhas been recently identified by thermodynamic methods like TGGE pre-selection and heteroduplex analysis. It was foundthat replication under thermal stress led to enormously high level of viroid mutagenesis. Mostly multiple mutants havingnon-random distribution of base changes were found. A specific "hot spots" were identified in the regions, wherea characteristic "pathogenicity domains" are localised in different viroids of the pospiviroidae family. Specific viroidmicroevolution was observed upon artificial inoculation of non-host plant species. Our results suggest that viroid propagationunder physiological stress can be assumed as important factor, which is among others, responsible for an appearanceof viroid quasi-species in the nature. Evolution and new viroid patotypes could accumulate due to environmental stressincluding various pollutants may be a potential danger for cultured plants.

Keywords

• viroid mutagenesis
• quasi-species
• dna heteroduplexes
• stress factors
• viroid pathotypes