Interactions of viroids with viruses, insects and plants

Keywords: pospiviroids, trans-encapsidation, insect transmission

Viroids are minute plant pathogens that make use of the host’s cellular machinery for their replication. They consist of single-stranded, non-enveloped, circular RNA that does not encode for any proteins. Since their discovery in 1971, many questions have been raised concerning their epidemiology and more specifically on how they are transmitted between plants. In recent years several members belonging to the Pospiviroidae have been found latently in many solanaceous ornamentals all over Europe. By now, the importance of mechanical transmission has been clearly demonstrated. However, other routes of transmission still need closer investigation. By mechanically inoculating naturally occurring weed species from various families, we explored whether these can act as reservoirs for viroids. Other transmission pathways for viroids involve associations with certain families of viruses and insects. These types of interactions, and their potential risks, need to be studied one step at a time. Starting with viroid-virus interactions, we study the phenomenon of “trans-encapsidation”, where viroid RNA gets encapsulated by virus particles. Using the virus as a transport vehicle, viroids might ultimately (co-)infect host plants of the virus. Demonstrating trans-encapsidation can be accomplished by means of different techniques based on double inoculations, virus/viroid purifications and enzymatic/(q)RT-PCR/microscopic detection. Here, we would like to present our preliminary results on viroid-plant & virus interactions and discuss possible avenues for future research.