Synthetic elements for enhancing expression of genes in plant cells are disclosed. These include a promoter with a 'TATA to start' sequence containing 64 % or greater GC content and a synthetic upstream element incorporating several OCS binding motifs and novel flanking sequences. Upstream activating regions (UARs) are also disclosed that can further increase the constitutive transcriptional activity when they are operably linked to said promoter and/or the synthetic upstream element. In particular, the nucleotide sequence of the UAR of the maize Ubi-1 gene is provided and its use in expression cassettes and vectors containing these promoter elements. Cells and plants transformed with these vectors are further provided. These include a transgenic sunflower expressing an exogenous oxalate oxidase gene at a high level under the transcriptional control of a recombinant promoter having at least one upstream activating region of the 35S CaMV promoter.