Effect of transcription terminator usage on the establishment of transgene transcriptional gene silencing.

Our experiments comparing plants with a LUC reporter under the 35S CaMV promoter and good efficiency terminators (Thsp, T35S) show that the use of efficient terminator sequences does not avoid the accumulation of promoter DNA methylation and transgene silencing. However, Thsp lead to a higher reporter gene expression and lower promoter DNA methylation levels than T35S, supporting that terminator usage is indeed involved in the establishment of TGS by methylation of transgenes' promoters. In the case of a terminatorless construct, the PTGS initiated by the improperly terminated mRNAs is not followed by the establishment of heritable silencing in the form of strong promoter DNA methylation, like in the case of TAS genes and reactivated TEs (for the transgene DNA methylation levels remained below the 20%).