Viroids are uncoated infectious RNA molecules (MW 107 OOO127 000) known as pathogens of certain higher plants. Thermodynamic and kinetic studies were carried out on highly purified viroid preparations by applying UV-absorption melting analysis and temperature jump methods. The thermal denaturation of viroids is characterized by high thermal stability, high cooperativlty and a high degree of bas...

We identified conditions for heating and quick cooling viroid RNAs in the presence of salt which lead to the production of conformational isomers stable to incubation for at least 45 minutes at 30 degrees in the presence of magnesium ions. Elution in 0.3 M NaCl allowed the purification of an electrophoretically slow form of an in vitro transcript carrying a complete copy of the potato spindle t...

Viroids are small self-replicating RNAs that infect plants. How these noncoding pathogenic RNAs interact with hosts to induce disease symptoms is a long-standing unanswered question. Recent experimental data have led to the suggestive proposal of a pathogenic model based on the RNA silencing mechanism. However, evidence of a direct relation between key components of the RNA silencing pathway an...

Abstract Background and Aims: Hop stunt viroid (HSVd, genus Hostuviroid, family Pospiviroidae) has a wide host range among trees and herbaceous plants. The objectives of this study were to compare biological and physical characteristics of three isolates of HSVd from mulberry, fig and citrus and search for other hosts of this viroid in Iran. Materials and Methods: Plant samples were col...

The 5' termini of linear forms of avocado sunblotch viroid (ASBVd) isolated from infected tissue have been determined by primer extension analyses. According to the different termini identified, four main populations of linear viroid molecules were found. One of them had the same 5' end as the one produced in the in vitro self-cleavage reaction of ASBVd dimeric transcripts mediated by a hammerh...

Previous attempts to develop RNAi-mediated viroid-resistant transgenic plants using nearly full-length Potato spindle tuber viroid (PSTVd) hairpin RNA (hpRNA) were successful; however unusual phenotypes resembling viroid infection occurred. Therefore, in the present work, transgenic Nicotiana benthamiana lines expressing both partial and truncated versions of PSTVd hpRNA were developed. Specifi...

Previous analysis of potato spindle tuber viroid (PSTVd) RNA-infected tobacco plants has suggested that an RNA-DNA interaction could trigger de novo methylation of PSTVd transgene sequences. Using the genomic sequencing technique, the methylation pattern associated with the RNA-directed DNA methylation process has been characterized. Three different PSTVd transgene constructs all showed a simil...

Viroids are self replicating non-coding RNAs capable of infecting a wide range of plant hosts. They do not encode any proteins, thus the mechanism by which they escape plant defenses remains unclear. RNAi silencing is a major defense mechanism against virus infections, with the four DCL proteins being principal components of the pathway. We have used Nicotiana benthamiana as a model to study Po...

This is an online database in order to facilitate research on viroid, viroid-like RNAs and human hepatitis delta virus by presenting a large number of sequences and related data in a comprehensive and user-friendly format (e.g., position of their self-catalytic domains, open reading frame, prediction of the most stable secondary structures, etc.). This online database is available on the WWW at...

The viroid and viroid-like RNA database is a compilation of all natural sequences published in journals or available from the GenBank and EMBL nucleotide sequence libraries. Several information regarding these RNA species such as the position of their self-catalytic domains and the open reading frame of the human hepatitits delta virus are provided. The database also includes a determination of...