Transcriptional gene silencing and RNA silencing in plants

Responsible : Thierry LAGRANGE (DR1 CNRS)

methylation de l'ADNCytosine DNA methylation is an epigenetic modification of DNA that is usually associated with the stable and heritable repression of transcription. In particular cytosine DNA methylation and heterochromatin formation is often observed on repetitive DNA probably as the consequence of the activation of genome defense mechanisms directed against transposons and other selfish DNA elements. Recently, many studies performed in fission yeast and plants, have revealed that the RNA-interference (RNAi) pathway, via the prodution of heterochromatic small RNA (sRNA), is also implicated in heterochromatin assembly and cytosine DNA methylation in plants. In the team, we study the plant sRNA-dependent DNA methylation pathway, also known as RdDM, in the model plant Arabidopsis thaliana, a model easily amenable to genetic and biochemical analysis. Our studies have revealed that 1) two form of a plant-specific RNAP II, PolIV and PolV, play complementary roles in the RdDM pathway (Pontier et al. 2005); 2) that PolV harbors both evolutionarily conserved and plant-specific subunits, in particular NRPE5 (Lahmy et al. 2009); 3) that ARGONAUTE4 (AGO4), the main AGO effectors mediating RdDM in plants, specifically interacts with PolV, via an extended carboxy-terminal domain (CTD) present in NRPE1, the PolV largets subunit (Li et al. 2006); 4) that NRPE1 exhibits AGO4-binding capacity through a previously unrecognized WG/GW (neighboring Tryptophan-Glycine/Glycine-Tryptophane residues), now known as AGO-hook (El-Shami et al. 2007).

More recently, using the AGO hook motif as a paradigm to characterize new AGO-binding component of the plant RNA silencing pathways, we have identify SPT5-like, a PolV-associated protein containing homology with the yeast transcription elongation factor SPT5, that interacts with AGO4 and is involved in RdDM (Bies-Etheve et al. 2009). We have also carried out an exhaustive bioinformatic analysis of the Arabidopsis genome and identified many potential AGO hook-containing proteins in Arabidopsis (Karlowski et al. 2010).

Our current work is focused on the mechanisms involved in the targeting of DNA methylation by PolV, using both genetic and biochemical approaches. We are also developing a systematic analysis of the novel proteins identified upon completion of the bio-informatic sreen. We hope that this approaches will help us learn more about RNAi and more specifically the mechanisms governing the formation and maintenance of heterochromatin in Arabidopsis.

We do not have available post-doctoral position for the moment. Candidates interested in the work performed in our laboratory and willing to apply to international post-doctoral fellowships are welcome.

Team :

AZEVEDO FAVORY Jacinthe - Chercheur CNRS

ETHEVE-BIES Natacha - Maître de conférences UPVD

KAIROUANI Alicia - Doctorante

LAGRANGE Thierry - Directeur de recherche CNRS

LAHMY Sylvie - Chercheur CNRS

LAUDIE Michèle - Assistant Ingénieur CNRS

PICART Claire - Assistant ingénieur CNRS

PONTIER Dominique - Chercheur CNRS

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