Australian grapevine viroid--evidence for extensive recombination between viroids.

Area of Science:

• Plant Pathology
• Virology
• Molecular Biology

Background:

• Viroids are small, non-protein-coding RNA molecules that infect plants.
• Existing viroid classifications are based on sequence similarity, with limited diversity observed.
• Grapevine cultivation has a long history, potentially exposing plants to multiple viroid infections.

Purpose of the Study:

• To characterize a novel viroid, Australian grapevine viroid (AGV), identified in grapevines.
• To determine the evolutionary origins and classification of AGV based on its sequence.
• To investigate the potential role of RNA recombination in the emergence of new viroids.

Main Methods:

• Full genome sequencing of the Australian grapevine viroid (AGV).
• Bioinformatic analysis to compare AGV sequence with known viroid sequences.
• Identification of conserved regions and assessment of sequence similarity.

Main Results:

• AGV exhibits less than 50% sequence similarity to any previously identified viroid.
• AGV's sequence contains regions homologous to citrus exocortis, potato spindle tuber, apple scar skin, and grapevine yellow speckle viroids.
• AGV possesses the entire central conserved region characteristic of the apple scar skin viroid group.

Conclusions:

• Australian grapevine viroid (AGV) is proposed as a new member of the apple scar skin viroid group.
• AGV's unique sequence suggests an origin through extensive RNA recombination between different viroids.
• Long-term cultivation of grapevines and exposure to multiple viroid infections may facilitate such recombination events.