Functional analysis of 5' untranslated region of a TIR-NBS-encoding gene from triploid white poplar.

Genome-wide analyses have identified a set of TIR-NBS-encoding genes in plants. However, the molecular mechanism underlying the expression of these genes is still unknown. In this study, we presented a TIR-NBS-encoding gene, PtDrl02, that displayed a low level of tissue-specific expression in a triploid white poplar [(Populus tomentosa x P. bolleana) x P. tomentosa], and analyzed the effects of the 5' untranslated region (UTR) on gene expression. The 5' UTR sequence repressed the reporter activity of beta-glucuronidase (GUS) gene under PtDrl02 promoter by 113.5-fold with a staining ratio of 2.97% in the transgenic tobacco plants. Quantitative RT-PCR assays revealed that the 5' UTR sequence decreased the transcript level of the GUS reporter gene by 13.3-fold, implying a regulatory role of 5' UTR in transcription and/or mRNA destabilization. The comparison of GUS activity with the transcript abundance indicated that the 5' UTR sequence decreased the translation efficiency of target gene by 88.3%. Additionally, the analysis of the transgenic P-985/UTRDelta/GUS plants showed that both the exon1 sequence and the leading intron within the 5' UTR region were responsible for the regulation of gene expression. Our results suggested a negative effect of the 5' UTR of PtDrl02 gene on gene expression.