The effect of oligodeoxyribonucleotides complementary to the region of the so-called pathogenicity domain (nucleotides 42-78) of the upper RNA strand of potato spindle tuber viroid (PSTVd) (severe) on viroid infection was investigated. The oligonucleotides were allowed to form hybrids with PSTVd in the infection mixtures before inoculation. Infectivity tests were performed using intact plants and plant protoplasts. It was found that the DNA oligonucleotides caused significant reduction of viroid infection at plant and single cell levels. The 200-fold molar excess of antisense DNA over viroid RNA is usually sufficient for the complete blocking of viroid infection. The inhibitory effect is strongly sequence specific. Inhibition by corresponding antisense RNA was much less efficient than that caused by antisense DNA.

Department of Molecular Genetics Academy of Sciences of the Czech Republik Ceské Budĕjovice