Interdependence of pathogenicity and replicability with potato spindle tuber viroid

Area of Science:

• Plant Pathology
• Virology
• Molecular Biology

Background:

• Viroids, such as potato spindle tuber viroid (PSTVd), can cause significant crop damage.
• The emergence and interaction of different viroid strains within a host are not fully understood.
• Understanding viroid evolution and pathogenicity is crucial for disease management.

Purpose of the Study:

• To investigate the spontaneous generation and characteristics of new PSTVd strains.
• To determine the competitive interactions between PSTVd strains of varying pathogenicity.
• To elucidate the molecular basis of PSTVd pathogenicity and replicability.

Main Methods:

• Isolation and sequencing of PSTVd strains from infected tomato plants.
• Inoculation experiments with single and mixed viroid strains.
• Quantification of viroid strains using nondenaturing polyacrylamide gel electrophoresis.
• Analysis of structural stability via temperature-gradient gel electrophoresis.

Main Results:

• Spontaneous generation of new PSTVd strains (RG 1, QF A, QF B) was observed.
• More pathogenic strains outcompeted less pathogenic ones, while similar strains coexisted.
• Mutations in the virulence-modulating region affected thermodynamic stability and transient structure accumulation.
• Viroid concentration remained similar across different strains and mixtures.

Conclusions:

• PSTVd strains can spontaneously arise and exhibit differential competitive abilities.
• The thermodynamic stability of the viroid's rod-like structure, influenced by mutations, correlates with pathogenicity.
• A model is proposed where the transient, replication-active structure is key to PSTVd pathogenesis.