Arabidopsis termination elements increase transgene expression in tobacco plants

Abstract

Post-transcriptional gene silencing (PTGS) greatly inhibits the use of transgenic plants in the agricultural and biotechnology industries. One cause of PTGS is transcription activated by nearby promoters that produces RNA transcripts that are complementary to the transgene. Therefore, strong termination elements flanking the transgene could potentially eliminate this type of silencing. Three potential sequences were identified in Arabidopsis thaliana between actively expressed plant genes with reading frames in a tail-to-tail orientation. We predicted that these elements have strong termination activity because these genes are expressed in all plant organs and structures and during all growth stages. In this study, we investigated the effects of these Arabidopsis termination elements (ATs) on the expression of transgenes encoding gusA and gfp and controlled by promoters of plant or viral origin. The presence of ATI and ATI-IV in the upstream region increased GFP expression from the constitutive promoters CaMV 35S and RuBisCo almost two-fold, and the construct flanked by ATI, ATI-IV and ATII enhanced RuBisCo-GFP expression approximately 2.3-fold. These ATs, however, had no effect on GUS expression when combined with a weak minimal 35S promoter and had very little effect on expression when combined with a shortened ELIP promoter. Finally, we also found that for strong promoters, especially in the case of the plant RuBisCo promoter, most of the variance component arises from differences between separate lines, but for weak promoters, approximately 60 % could be attributed to differences among the clones.