Viroids, small circular RNAs that replicate independently and in most cases incite diseases in plants, are classified into the families Pospiviroidae, composed of species with a central conserved region (CCR) and without hammerhead ribozymes, and Avsunviroidae, composed of three members lacking CCR but able to self-cleave in both polarity strands through hammerhead ribozymes. Here we report the biological and molecular properties of Eggplant latent viroid (ELVd). Purified circular ELVd induces symptomless infections when inoculated into eggplant seedlings. ELVd can be transmitted horizontally and through seed. Sequencing 10 complete cDNA clones showed that ELVd is a circular RNA of 332 to 335 nucleotides with high variability. This RNA can adopt a quasi-rod-like secondary structure of minimal free energy and alternative foldings that permit formation of stable hammerhead structures in plus and minus strands. The ribozymes are active in vitro and, most likely, in vivo. Considering the ELVd properties to be intermediate between those of the two genera of family Avsunviroidae, we propose ELVd as the type species of a third genus with the name Elaviroid.Viroids and satellite RNAs have been implicated in several plant diseases. Whereas viroids replicate autonomously (12), satellite RNAs depend functionally on helper viruses and are encapsidated by their coat proteins (17). A survey in Eastern Spain for detecting small infectious RNAs in vegetables identified a viroid-like RNA in eggplant (Solanum melongena L. cv. Sonja) (8). Denaturing polyacrylamide gel electrophoresis (PAGE) revealed two bands with the mobilities expected for the circular and linear forms, and treatment with RNase, but not with DNase, caused their disappearance. Inoculation of eggplant seedlings with preparations containing the viroid-like RNA showed the presence of the same RNA in some of the inoculated plants, which remained symptomless, and its absence in the noninoculated controls. On this basis, the RNA was named Eggplant latent viroid (ELVd), although the possibility that it could be a viroid-like satellite RNA could not be dismissed (8). Attempts to transmit ELVd to tomato, chrysanthemum, cucumber, and citron, which support the replication of different viroids, failed, suggesting a restricted host range, and riboprobes specific for Citrus exocortis viroid (CEVd), Hop stunt viroid, and Apple scar skin viroid did not hybridize with ELVd, suggesting that it was not a member of the genus Pospiviroid, Hostuviroid, or Apscaviroid (8). These genera belong to the family Pospiviroidae, whose members have a central conserved region and lack hammerhead ribozymes (12). These data, together with the low stability of ELVd circular forms in vitro (9), were indicative of a peculiar structure and prompted us to study the biological and molecular properties of ELVd.Biological properties of ELVd. Eggplant seedlings (cv. Redonda morada) inoculated with ELVd and kept in a greenhouse were used as the source of ELVd. To confirm that ELVd could replicate autonomous...

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