"Hormone-Mediated Gene-Specific Translation Regulation"

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Thursday 28 June 2018, 14:00 - 15:30

 
ABSTRACT

The central role of translation regulation in the control of critical cellular processes has long been recognized. Yet the systematic exploration of quantitative changes in translation at a genome-wide scale in response to specific stimuli has only recently become technically feasible.

Using a genetic approach, we have identified new Arabidopsis weak-ethylene insensitive mutants that also display defects in translation, which suggested the existence of a previously unknown molecular module involved in ethylene-mediated translation regulation of components of this signaling pathway. To explore this link in detail, we implemented the ribosome-footprinting technology for Arabidopsis, which enables the study of translation at a whole-genome level at single codon resolution [1]. Using ribosome-footprinting we examined the effects of a short exposure to ethylene on the Arabidopsis translatome looking for ethylene-triggered changes in translation rates that could not be explained by changes in transcript levels. The results of this research, in combination with the characterization of a subset of the aforementioned weak ethylene insensitive mutants that are defective in the UPF genes (core-components of the nonsense-mediated mRNA decay machinery), uncovered a translation-based branch of the ethylene signaling pathway [2]. In the presence of ethylene, translation of EBF2, a negative regulator of ethylene signaling, is repressed, despite being transcriptionally induced. These translational effects of ethylene require the long 3´UTR of EBF2 (3´EBF2), and the C-terminal end of the key ethylene-signaling protein EIN2 (EIN2C). After ethylene perception, EIN2C is released from the ER-membrane by proteolytic cleavage and binds the 3´EBF2 in the cytoplasms, it also recruits the UPF proteins and moves the complex to P-bodies, where the translation of EBF2 in inhibited despite its mRNA accumulation. Once the ethylene signal is withdrawn, the translation of the stored EBF2 mRNAs is resumed, thus rapidly dampening the ethylene response. These findings represent a mechanistic paradigm of gene-specific regulation of translation in response to a key growth regulator.

Translation regulatory elements can be located in both 3? and 5? UTRs. We are now focusing on the ead1 and ead2 mutants, another set of ethylene-signaling mutants defective in translational regulation. Ribosome-footprinting on the ead1 mutant revealed an accumulation of translating ribosomes in the 5´UTRs of uORF-containing genes and reduction in the levels of ribosomes in the main ORF. The mutant is also impaired in the translation of GFP when this reporter is fused to WT 5´UTR of potential EAD1 targets but not when GFP is fused to the uORF-less versions of the same 5´UTRs. Our hypothesis is that EAD1/2 work as a complex that is required for the efficient translation of mRNAs that have common structural (complex 5´UTR with uORFs) and functional (regulation of key cellular processes) features. We are working towards the identification of the conditions where the EAD1 regulation of translation is required.

 

[1] Ingolia, N. et al. (2009) Science, 324; 218-222

[2] Merchante, C. et al. (2015) Cell, 163(3): 684-697

Location Jozef Schell Seminar Room
Contact Dr Catharina Merchante
University of Málaga
Department of Molecular Biology and Biochemistry
SPAIN