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Silencing transcriptionnel et méthylation de l’ADN chez Arabidopsis thaliana

Abstract : Transcriptional silencing is an essential mechanism for controlling the expression of genes, for instance, depending on the developmental stage, and for blocking transcription of transposable elements (TEs), the expression of which can be deleterious. This mechanism is dependent of various chromatin modifications such as DNA methylation and histone post-translational modifications. Transcriptional silencing is commonly associated with high levels of DNA methylation and release of silencing is frequently observed in mutants for genes involved in DNA methylation maintenance. However, methylated genes and TEs can accumulate other silencing layers some of which may operate independently of DNA methylation. Through two distinct studies and approaches we sought to identify and understand these DNA methylation-independent pathways in the model plant Arabidopsis thaliana.Using a forward genetic approach with a silenced transgene we show that the DNA helicase REGULATOR OF TELOMERE ELONGATION 1 (RTEL1), implicated in DNA replication, is involved in the silencing of a set of genes and TEs. Loss of silencing in the rtel1 mutant is not correlated with a decrease in DNA methylation levels nor with heterochromatin organization defects. Yet, many heterochromatic loci show an increase in DNA methylation levels associated with an increase in chromatin accessibility. Loss of silencing and DNA hypermethylation seem to be consequences of the rtel1-induced replicative stress. Thus, our findings reveal a function for RTEL1, which might be linked to DNA replication, in maintaining silencing and in preventing heterochromatin DNA hypermethylation.We also investigated the different silencing layers which control the expression of the TE Evadé. In absence of CG methylation, silencing of this element is maintained by another pathway in young tissues but not in adult tissues. Our data suggest that this pathway may be mediated by the trimethylation of histone H3 lysine 27 (H3K27me3) present in young tissues and likely lost in adult tissues. This tissue-specific control could be a global mechanism which targets other TEs of the Arabidopsis genome.
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Submitted on : Thursday, June 2, 2022 - 11:10:39 AM
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Amy Hesketh. Silencing transcriptionnel et méthylation de l’ADN chez Arabidopsis thaliana. Sciences agricoles. Université Clermont Auvergne, 2021. Français. ⟨NNT : 2021UCFAC064⟩. ⟨tel-03685548⟩

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