Post-transcriptional gene silencing is involved in resistance of transgenic papayas to papaya ringspot virus

Transgenic papayas carrying the papaya ringspot virus coat protein gene were inoculated with Papaya ringspot virus. Infection was monitored by evaluating symptoms and by reverse transcription polymerase chain reaction (RT-PCR). Among eight tested transgenic lines, clone G2 was found highly resistant to virus infection during 3 years of testing. Further analysis of this clone revealed complex multicopy transgene insertion with aberrant copies. The suspected post transcriptional gene silencing was confirmed by siRNA detection. While the R0 generation of G2 transgenic papaya was found to be fully resistant to the infection, Papaya ringspot virus was able to break this resistance in subsequent generations by suppressing post-transcriptional gene silencing (PTGS).