Post-transcriptional gene silencing in plum pox virus resistant transgenicEuropean plum containing the plum pox potyvirus coat protein gene

Transgenic plums containing the plum pox potyvirus coat protein (PPV-CP) ge ne were inoculated with PPV. Infection was monitored by evaluating symptoms , ELISA, and IC-RT-PCR. Transgenic clone C5 was highly resistant to PPV dur ing four years of testing and displayed characteristics typical of post-tra nscriptional gene silencing (PTGS), including a high level of transgene tra nscription in the nucleus, low levels of transgene mRNA in the cytoplasm, a complex multicopy transgene insertion with aberrant copies, and methylatio n of the silenced PPV-CP transgene. The PPV-CP transgene was also methylate d in seedlings of C5 and these seedlings were resistant to PPV. Our results show, for the first time, that PTGS functions as a mechanism for virus res istance in a woody perennial species.