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.