Viroids are the smallest autonomously replicating pathogenic agents yet described -- small, highly structured, circular RNA molecules which lack the protective protein capsid and mRNA activity characteristic of nearly all conventional plant viruses. Viroid diseases are responsible for significant losses of food and fiber, and several viroids (e.g., potato spindle tuber viroid or PSTVd) are currently subject to quarantine regulation.

Mutational analysis of PSTVd and several related viroids has allowed us to genetically isolate and dissect such normally interrelated processes as replication, cell-to-cell movement, and disease induction. Furthermore, we have begun to explore the possibility of exploiting certain beneficial consequences of viroid infection.

Current objectives include:
• Identify the normal cellular pathways used by viroids to enter and exit the nucleus, move from cell to cell, and transit the vascular system;
• Characterize the host response to viroid infection at the molecular level, with special emphasis on viroid interaction with host proteins (e.g., protein kinases); and
• Use this information to design and test novel strategies for creating (i) durable resistance to viroid disease and (ii) an improved citrus dwarfing agent.