A uORF represses the transcription factor AtHB1 in aerial tissues to avoid a deleterious phenotype

RIBONE, PAMELA A.; CAPELLA, MATÍAS; ARCE, AGUSTÍN L.; CHAN, RAQUEL L.

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Año: 2017 vol. 175 p. 1238 - 1253

0032-0889

AtHB1 is anArabidopsis homeodomain-leucine zipper transcription factor that participatesin hypocotyl elongation under short day conditions. Here we show that itsexpression is post-transcriptionally regulated by an upstream open readingframe (uORF) located in its 5? UTR. This uORF encodes a highly conservedpeptide (CPuORF), present in varied monocot and dicot species. The ArabidopsisuORF and its maize homolog repressed the translation of the main ORF in cis,independent of the sequence of the latter. Published ribosome footprintingresults and the analysis of a frame shifted uORF, in which the repressioncapability was lost, indicated that the uORF causes ribosome stalling. The regulationexerted by the CPuORF was tissue-specific and did not act in the absence oflight. Moreover, a photosynthetic signal is needed for the CPuORF action sinceplants with uncoupled chloroplasts did not show uORF-dependent repression.Plants transformed with the native AtHB1 promoter driving AtHB1expression did not show differential phenotypes, whereas those transformed witha construct in which the uORF was mutated exhibited serrated leaves, compactrosettes, and most significantly, short non-dehiscent anthers and siliquescontaining fewer or no seeds. We thus propose that the uncontrolled expressionof AtHB1 is deleterious for the plant and hence, finely repressed by atranslational mechanism.