The 5′-untranslated region of the tobacco Alcohol dehydrogenase gene functions as an effective translational enhancer in plant

The alcohol dehydrogenase gene (NtADH) was previously isolated from tobacco BY2 suspension cultured cell. Expression of this gene was dramatically increased only during the early stationary phase, and the 5'-untranslated region (5'-UTR) was hypothesized to be involved in the stimulatory effect at the post-transcriptional level. In this paper, we investigated whether the NtADH 5'-UTR possesses the ability to positively enhance gene expression at the translational level. For easily estimating translational efficiency, we used beta-glucuronidase (GUS) gene as a reporter and tobacco BY2 cell, Arabidopsis thaliana T87 cell, and rice Oryza sativa suspension cultured cells as host cells in a transient assay system. Compared with the control plasmid pBI221, insertion of the NtADH 5'-UTR enhanced GUS expression levels about 30- to 100-fold and 30- to 60-fold in transiently transformed BY2 and T87 cells, respectively. However, in transiently transformed O. sativa cells, expression was barely enhanced. In comparison with the 5'-UTR of tobacco mosaic virus (Omega sequence), a known translational enhancer, the NtADH 5'-UTR enhanced translation to a similar level. Meanwhile, the translational efficiency was affected by the sequence context around the AUG initiation codon at the translational initiation step. Moreover, this NtADH 5'-UTR also worked in stable tobacco transformants. Therefore, it is expected that this 5'-UTR will serve as a powerful tool for enhancing foreign gene expression.