Suppression of transgene RNA silencing in transgenic Arabidopsis thaliana by a mild strain of Cucumber mosaic virus

The ability of Cucumber mosaic virus (CMV) subgroup II strain CMV-KT to suppress RNA silencing via posttranscriptional gene silencing (PTGS) was determined using Turnip mosaic virus (TuMV)-resistant transgenic Arabidopsis thaliana (TuR-At) carrying TuMV coat protein (CP) transgenes. CMV-KT induced only slight growth retardation in TuR-At plants, but no dwarf or mosaic symptoms, while subgroup I strain Y (CMV-Y) caused severe symptoms. Expression of the RNA-silenced TuMV-CP transgene resumed and produced TuMV-CP in either CMV-KT- or CMV-Y-infected TuR-At plants, indicating that the RNA silencing of the TuMV-CP gene was suppressed. Challenge inoculation experiments revealed that RNA silencing of the TuMV-CP transgene by CMV-KT infection is suppressed mostly in young developing leaves, but not in mature leaves, of TuR-At plants. These results demonstrated that transgene-derived virus resistance in transgenic Arabidopsis plants can be compromised by even a mild strain of CMV infection.