The 3' non-coding region of a C4 photosynthesis gene increases transgene expression when combined with heterologous promoters.

The Me1 gene of the dicot Flaveria bidentis encodes NADP malic enzyme, which catalyses the decarboxylation reaction of C4 photosynthesis in bundle sheath cells. We have previously shown that the 3' non-coding region (Me1 3') controls quantitative expression of the gene. We wondered whether Me1 3' can increase expression when combined with heterologous promoters. We tested a highly expressed, constitutive promoter, the S4 promoter from subterranean clover stunt virus, and a highly expressed, leaf-specific promoter, the light-harvesting chlorophyll a/b-binding protein gene 3 (Lhcb3) promoter of Arabidopsis thaliana. Promoter-3'-end combinations were tested in transgenic C4 Flaveria plants and C3 tobacco. We found that Me1 3' increased expression of the gusA reporter gene several-fold in leaves of both species in combination with either of the promoters. In both cases Me1 3' does not alter the expression pattern for either promoter. We conclude that Me1 3' can be used as a transcription terminator to increase transgene expression in C3 dicot plants.