Primary and secondary structure of a new viroid ‘species’ (CbVd 1) present in theColeus blumeicultivar ‘Bienvenue’

The detection of a viroid in Coleus blumei species in Brazil (1) has prompted us to search for viroids in C. blumei cultivars (cvs) commercially propagated by cuttings for more than 50 years in Germany. 'Return' PAGE (2) of nucleic acid extracts from the cv 'Bienvenue' revealed a band of circular viroid-like RNA molecules. Northern blot analysis (3) with radioactive probes specific for viroids representative for the currently known viroid groups (4) did not exhibit any signals indicating that this circular RNA might represent a new viroid 'species'. This also precluded the use of known viroid-specific DNA primers for the reverse transcription and sequence analysis of this RNA. Consequently, the sequence of parts of it was established by direct RNA sequencing (5), which allowed the synthesis of DNA primers specific for the reverse transcription of the new viroid. Its isolation, purification and sequence analysis by primer elongation were performed as described (6). The sequence and the secondary structure model of the 248 nt long new viroid, tentatively named Coleus blumei viroid 1 (CbVd 1), are shown in the figure.