High level expression of transgenes by use of 5 '-untranslated region of the Arabidopsis thaliana arabinogalactan-protein 21 gene in dicotyledons

For higher expression of a foreign gene in plant cells, it is important to optimize nucleotide sequences corresponding to 5'-untranslated region (5'-UTR), because it usually has great impacts on the expression of the gene mainly at the translational level. In this study, with an aim to find useful 5'-UTRs, thirty nine 5'-UTRs derived from Arabidopsis thaliana genes were tested by transient expression of firefly luciferase (Fluc), and that of A. thaliana arabinogalactan-protein 21 (AtAGP21) gene was selected for further analyses. Its activity was either equaling or surpassing that of known translational enhancer, A. thaliana alchol dehydrogenase (AtADH) 5'-UTR in dicotyledons, and was further improved by the optimizing sequence context of the initiating codon (-3 to -1 of AUG). Finally, we also found that the modified AtAGP21 5'-UTR was useful in recombinant expression of horseradish peroxidase (HRP) in tobacco cultured cells, and the yield was as much as 23 mgl(-1) culture medium in seven days.