The DNA form of a retroviroid-like element characterized in cultivated carnation species

Carnation small viroid-like RNA (CarSV RNA) is a small (275 nt), circular molecule which is unique among plant viroid-like RNAs in having a tandemly repeated homologous DNA. This DNA form was found fused to DNA sequences of carnation etched ring caulimovirus (CERV) in certain Spanish carnation plants. The observation of a growth abnormality consisting of extensive shoot proliferation in cultivated carnations in Hungary prompted the molecular analysis of these plants, in which both CarSV RNA and DNA forms were detected. Several CarSV DNA sequences were characterized in various Dianthus caryophyllus cultivars which were symptomless or showed different symptoms. CarSV DNA forms showing minor sequence heterogeneities and deletions occurred in the same plant. Unit-length CarSV DNA sequences were proven to accumulate in the plant cell nucleus. The plants studied here were not infected by any of the viruses (including CERV) or other cellular pathogens described previously in carnation.