Efficient transgene expression by alleviation of translational repression in plant cells

Identification of 5'-untranslated regions that function as effective translational enhancers in monocotyledonous plant cells using a novel method of genome-wide analysis

High expression of a transgene is often necessary to produce useful substances in plants. The efficiency of mRNA translation is an important determinant of the level of transgene expression. In dicotyledonous plants, the 5'UTR of certain mRNAs act as translational enhancers, dramatically improving transgene expression levels. On the other hand, translation enhancers derived from dicotyledonous plants are not so much effective in monocotyledonous plants, which are important as industrial crops and as hosts for production of useful substances. In this study, we evaluated the polysome association on a large scale with high resolution for each 5'UTR variant from multiple transcription start site in normal and heat-stressed Oryza sativa suspension cultures. Translational enhancer candidates were selected from the resultant large-scale data set, and their enhancer activities were evaluated by transient expression assay. In this manner, we obtained several translational enhancers with significantly higher activities than previously reported enhancers. Their activities were confirmed in a different monocotyledonous plant, Secale cereale, and using a different reporter gene. In addition, enhancer activities of tested 5'UTRs were different between monocotyledonous and dicotyledonous plants, suggesting that the enhancer activities were not compatible between them. Overall, we demonstrate these useful 5'UTRs as enhancer sequence for transgene expression in monocotyledonous plants.

Arabidopsis thaliana cold-regulated 47 gene 5'-untranslated region enables stable high-level expression of transgenes

Transgene expression is regulated through several steps, this study focuses on the mRNA translation step. The expression level of transgenes can be increased by 5'-untranslated region (5'UTR) sequences in certain genes which act as translational enhancers. On the other hand, translation in most mRNA species is repressed by growth, development, and stress events. There is a possibility that transgene mRNA is also repressed in these conditions, despite the use of a translational enhancer. Therefore, a consistently efficient translational enhancer is needed to develop a reliable transgene expression system. Herein we searched for mRNAs translated stably under different growth, development and environmental conditions using data sets of polysome fraction assays and microarray analysis. Correct 5'UTR sequences of candidate genes were determined by cap analysis of gene expression and we tested translational ability of the candidate 5'UTRs by reporter assays. We found the 5'UTR of cold-regulated 47 gene to be an effective translational enhancer, contributing to stable high-level expression under various conditions.