ABSTRACT
Viroids are small, single-stranded, highly structured, circular RNAs that replicate autonomously in their hosts, without messenger RNA activity. Because they do not encode for proteins, viroids have to interact directly with host factors. This review presents recent progress in understanding the possible role of recently identified viroid-binding host proteins related to replication, trafficking and pathogenesis. It also discusses some aspects on viroid evolution. In recent years, efforts to understand how viroids replicate, cause disease and induce symptoms have prompted details on molecular mechanisms related to the viroid infectious cycle. Inasmuch as viroids lack protein-encoding capacity, including suppressors of gene silencing, their existence could be ensured by their compact conformation, compartimentalization in organelles, association with host factors or by their highly efficient replication. The complexity of the infectious cycle of these tiny pathogenic RNAs indicates that several interactions with host factors remain to be identified.
KEY WORDS
Avsunviroidae
;
Pospiviroidae
; RNA silencing; L5; TFIIIA