NUCLEOTIDE-SEQUENCE OF THE ORIGINAL BRAZILIAN ISOLATE OF COLEUS YELLOW VIROID FROM SOLENOSTEMON SCUTELLARIOIDES AND INFECTIVITY OF ITS COMPLEMENTARY-DNA

The complete nucleotide (nt) sequence of the original coleus yellow vi roid (CYVd) from Solenostemon scutellarioides, 'Golden Bedder', has be en determined. The covalently closed single-stranded CYVd RNA molecule consists of 248 nt residues which assumes a rod-like secondary struct ure when folded in the model of lowest free energy. The sequence was d etermined by direct sequencing of RNA and from three overlapping cDNA clones. Comparison of the CYVd sequence with that of Coleus blumei vir oid 1 (CbVd 1) from Germany demonstrated that they are closely related . The differences observed in the genome organization of CYVd relative to CbVd 1 were at three sites: position 25 (one U deletion), position 26 (a U was replaced by an A) and position 241 (one A insertion). The first two mutations were detected in one A-rich segment of eight nt ( between positions 25 and 34). Northern blot hybridization of partially purified nucleic acids from the leaf tissue of S. scutellarioides 'Fr illed Fantasy', inoculated with souble-stranded cDNA, demonstrated tha t this fragment was infectious. These data enable CYVd to be assigned to the viroid class of plant pathogens, based on its biological proper ties and molecular structure. This work also gives additional support to the present classification system, in which the viroids isolated fr om S. scutellarioides form a distinct subgroup.