Lecture – Francesco Di Serio

Viroids are small (230-450 nt) non-protein coding RNAs infecting and causing diseases in plants. In the absence of viroid-encoded proteins, infectivity and pathogenesis of these infectious agents completely rely on host proteins and/or on catalytic activities (ribozymes) endowed in their own RNA. In this seminar, besides presenting general features of viroids and viroid-like RNAs (such as hepatitis delta and delta-like viruses infecting humans and other vertebrates), I will focus on recent advances in their pathogenesis and host colonization pathways. Moreover, the potential implications of the recent discovery of more than 20000 coding and non-coding viroid-like RNAs in different geographic areas and ecological niches, and the structural and biological features of novel infectious agents -hybrids of viroid-like elements and RNA viruses replicating in fungi- will be presented and discussed.