The translation of the Arabidopsis AtHB1 gene is repressed in the aerial part of the plant by an Open Reading Frame present in its 5?UTR

CHAN RL; CAPELLA M; RIBONE PA

Buenos Aires

Simposio; Fronteras en Biociencias II; 2016

AtHB1 is an Arabidopsis transcription factor (TF) belonging to the HD-Zip I subfamily. The AtHB1 gene is expressed in hypocotyls and roots and previously it was demonstrated that AtHB1 acts downstream of PIF1 to regulate the expression of genes involved in the elongation and synthesis of the cell wall, by interacting with AtTBP2. Here we show that bioinformatic analyses considering AtHB1 homologues in several plant species resulted in the detection of a conserved upstream Open Reading Frame (uORF) in the 5?UTR region of these genes, named CPuORF33. These uORFs exhibit a higher degree of conservation in the aminoacidic sequences than in the nucleotide ones, and they do not overlap with the mORF (main ORF). Generation of different constructs, bearing the native or/and the mutated uORF, used to transform Arabidopsis plants allowed us to demonstrate that the CPuORF33 represses the mORF translation but not transcription, independently on the mORF nature. This regulation occurs in cis, probably through a ribosome stalling mechanism, in the aerial part of the plant but it does not occur in roots. On the other hand, AtHB1 overexpression is also repressed by small RNAs in Arabidopsis. It is worth noting that AtHB1 overexpression cause severe abnormalities in the reproductive organs of the plant. Altogether, our results reveal a novel mechanism by which the expression of AtHB1 (and that of its homologues in other plant species) is tightly regulated in order to avoid aberrant phenotypes observed when the TF is overexpressed leading to sterile plants.