Control of gene expression is achieved at various levels; transcription control, post-transcriptional processing, mRNA stability, translation, post-translational modifications and protein degradation. From early embryonic development to cell differentiation, metabolism, stress response, translation is used to fine-tune protein levels. A very interesting translational repression mechanism is the one performed by Upstream open reading frames (uORFs). uORFs are translational reading frames present in the 5’ leader region of eukaryotic mRNAs. The presence of uORFs usually inhibits translation of the downstream major ORF (main protein). Although uORFs are widespread in eukaryotic genomes, conserved peptides uORFs (CPuORFs) occur in less that 1% of transcripts. The uORFs studied in plants belong to three characterized CPuORF families that are involved in control translation of the major ORF in response to sucrose, polyamines and phosphocoline.
In plants, 39 CPuORFs families had been identified by bioinformatics analysis. In flowering plants, close to 80 % of the CPuORF families play a variety of regulatory roles, from transcriptional control to protein turnover, and from small signal molecules to signal transduction kinases. There is a strong association of CPuORFs with regulatory genes and genes that response to abiotic stress. Selective translation of transcripts plays an important role in plant acclimation and stress responses. CPuORFs genes represent a specific class of selectively translated genes. The three families whose CPuORFs have been analyzed experimentally regulate the major ORF in response to a small molecule (sucrose, polyamines and phosphocoline), thus it may be that other CPuORFs found by bioinformatics analysis also exhibit small molecule regulation. We are interested in studying the evolutionary conservation and biological function of uORFs in land plants using Marchantia polymorpha as a key node for comparative genomics analysis.
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