This project is aimed at the molecular characterization of
structure-function relationships involved in viroid-host cell interaction. The experimental system will be peach latent mosaic viroid (PLMVd) infecting peach seedlings. PLMVd is a non-typical viroid since contrary to most other members of the family, contains hammerhead ribozymes that are involved in vitro, and very probably in vivo, in the self-cleavage of their strands of both polarities. The existence of several natural isolates of PLMVd of different pathogenicity together with the relatively short time required for the induction of symptoms, makes this system very attractive. Full-length cDNA clones of PLMVd, constructed by reverse transcription-PCR amplification, will be used to infect peach seedlings in order to map regions involved in replication and/or pathogenesis. Site-directed mutagenesis will allow to determine the importance of specific residues within these regions as well as to confirm and characterize elements of tertiary structure in PLMVd.