The 5′ untranslated region of the VR-ACS1 mRNA acts as a strong translational enhancer in plants

The structure and function of untranslated mRNA leader sequences and their role in controlling gene expression remains poorly understood. Previous research has suggested that the 5′ untranslated region (5′UTR) of the Vigna radiata aminocyclopropane-1-carboxylate synthase synthase (VR-ACS1) gene may function as a translational enhancer in plants. To test such hypothesis we compared the translation enhancing properties of three different 5′UTRs; those from the VR-ACS1, the chlorophyll a/b binding gene from petunia (Cab22L; a known translational enhancer) and the Vigna radiata pectinacetylesterase gene (PAE; used as control). Identical constructs in which the coding region of the β-glucuronidase (GUS) gene was fused to each of the three 5′UTRs and placed under the control of the cauliflower mosaic virus 35S promoter were prepared. Transient expression assays in tobacco cell cultures and mung bean leaves showed that the VR-ACS1 and Cab22L 5′UTRs directed higher levels of GUS activity than the PAE 5′UTR. Analysis of transgenic Arabidopsis thaliana seedlings, as well as different tissues from mature plants, confirmed that while transcript levels were equivalent for all constructs, the 5′UTRs from the VR-ACS1 and Cab22L genes can increase GUS activity twofold to fivefold compared to the PAE 5′UTR, therefore confirming the translational enhancing properties of the VR-ACS1 5′UTR.