RNA plays an important role in transferring genetic information from DNA to protein during gene expression that is key to growth and development of a plant or animal. Recent studies have discovered that RNA itself has many novel biological roles apart from participating in protein synthesis. Some RNAs can control the expression of certain genes that is important for development and physiology of many organisms. Small RNAs of approximately 20 nucleotides produced from plant viruses and viroids during infection are believed to guide a host defense system to suppress the replication of these pathogens. It is hypothesized that some small RNAs derived from plant viruses and viroids can also regulate expression of selective host genes to promote infection and cause diseases. This novel concept implies that viral pathogens do not only use proteins, but also use small RNAs, to manipulate host metabolism to achieve infection. This hypothesis will be tested by investigating the formation and function of small RNAs derived from Potato spindle tuber viroid during infection as a model system. Combined genetic and biochemical experiments will be used to determine the molecular pathway that produces these small RNAs. Further biochemical and molecular experiments will be conducted to determine whether these small RNAs can regulate the expression of selected host genes and whether altered expression of a host gene contributes to symptom development. Results from these investigations will provide important information to advance understanding of how plant pathogens accomplish infection and causes diseases in an infected plant. They may also provide useful information to study the role of RNA during infection of animals and humans by viruses. Finally, the results may provide valuable clues to develop novel RNA-based tools to study gene functions in plants.
