EXPRESSION OF THE POTATO LEAFROLL VIRUS ORF0 INDUCES VIRAL-DISEASE-LIKE SYMPTOMS IN TRANSGENIC POTATO PLANTS

The role of the open reading frame 0 (ORF0) of luteoviruses in the vir al infection cycle has not been resolved, although the translation pro duct (p28) of this ORF has been suggested to play a role in host recog nition, To investigate the function of the potato leafroll luteovirus (PLRV) p28 protein, transgenic potato plants were produced containing the ORF0. In the lines in which the ORF0 transcripts could be detected by Northern (RNA) analysis, the plants displayed an altered phenotype resembling virus-infected plants. A positive correlation was observed between levels of accumulation of the transgenic transcripts and seve rity of the phenotypic aberrations observed, In contrast, potato plant s transformed with a modified, untranslatable ORF0 sequence were pheno typically indistinguishable from wild-type control plants. These resul ts suggest that the p28 protein is involved in viral symptom expressio n, Southern blot analysis showed that the transgenic plants that accum ulated low levels of ORF0 transcripts detectable only by reverse trans cription-polymerase chain reaction, contained methylated ORF0 DNA sequ ences, indicating down-regulation of the transgene provoked by the put atively unfavorable effects p28 causes in the plant cell.