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Correlation between bending of the VM region and pathogenicity of different Potato Spindle Tuber Viroid strains
1Institut für Physikalische Biologie, Heinrich-Heine-Universität Düsseldorf, Germany.
Abstract:
Only 40 of the 359 nucleotides of Potato Spindle Tuber Viroid (PSTVd) represent the virulence-modulating (VM) region. Minor sequence variations in this domain distinguish mild from severe and even necrotic strains. Our recent hypothesis (Owens RA et al., 1996, Virology 222:144-158) that these differences result in varying degrees of bending of this part of the molecule could be tested experimentally. By in vitro transcription and partial double-strand formation, three types of model RNAs were prepared and subjected to electrophoresis in polyacrylamide gels: (1) Fragments representing the VM regions of six different PSTVd strains; (2) control fragments containing a bulge-loop as a rigid bend or an internal loop as a point of increased flexibility; and (3) dsRNAs of 36, 39, and 43 bp as length standards. Migration anomalies in gels of increasing percentage were evaluated and resulted in the following conclusions. In the absence of Mg2+, the VM regions differ only in terms of flexibility. Addition of Mg2+ induces conformational changes in these RNAs. All strains but Mild exhibit a rigid bend, and the angle of bending increases monotonically with the pathogenicity of the strain. The data are discussed in terms of a mechanism of pathogenicity, that protein-binding to the VM region is the primary pathogenic event.
Insights
Potato Spindle Tuber Viroid (PSTVd) virulence-modulating regions bend differently based on strain pathogenicity. This structural change, induced by Mg2+, suggests a mechanism for viroid-host interactions and disease severity.
Area of Science:
- Plant virology
- Molecular biology
- Biophysics
Background:
- Potato Spindle Tuber Viroid (PSTVd) causes significant crop damage.
- The virulence-modulating (VM) region, a small part of the viroid, contains sequence variations linked to disease severity.
- Previous hypotheses suggested these variations might affect RNA bending.
Purpose of the Study:
- To experimentally test the hypothesis that sequence variations in the PSTVd VM region cause differential molecular bending.
- To investigate the role of Mg2+ in inducing conformational changes within the VM region.
- To correlate RNA bending with viroid pathogenicity.
Main Methods:
- In vitro transcription and partial double-strand formation to create model RNAs.
- Polyacrylamide gel electrophoresis to analyze RNA migration.
- Evaluation of migration anomalies in varying gel percentages to infer structural properties.
Main Results:
- In the absence of Mg2+, VM regions showed only differences in flexibility.
- Upon Mg2+ addition, conformational changes occurred, inducing rigid bending in all but the mild PSTVd strain.
- The angle of bending increased proportionally with the pathogenicity of the viroid strain.
Conclusions:
- Mg2+-induced bending of the PSTVd VM region is strain-dependent and correlates with pathogenicity.
- This differential bending may be a key factor in viroid-host interactions and disease development.
- Protein binding to the VM region is proposed as the primary pathogenic event, influenced by RNA conformation.