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22 juin 2018: 2 événements

  • Département Biologie des Génomes

    Vendredi 22 juin 10:00-11:00 - Angélique Déléris - Institut de biologie de l’Ecole normale supérieure IBENS, Paris

    Transcriptional control and exploitation of an immune-responsive family of plant retrotransposons

    Résumé : Mobilization of transposable elements (TEs) in plants has been recognized as a driving force of evolution and adaptation, in particular by providing genes with regulatory modules that impact their transcription. In the work that I will present, we employed an ATCOPIA93 Long terminal repeats (LTR) promoter-GUS fusion to show that this retrotransposon behaves like an immune-responsive gene during plant defense in Arabidopsis. We also showed that the reactivation of the endogenous ATCOPIA93 copy “EVD”, in the presence of bacterial stress, is not only negatively regulated by DNA methylation but also by Polycomb-mediated silencing¬—a mode of repression typically found at protein-coding and microRNA genes. Interestingly, one of the ATCOPIA93-derived soloLTRs is located upstream of the disease resistance gene RPP4 and is devoid of either DNA methylation or H3K27m3 marks. Through loss-of-function experiments, we demonstrated that this soloLTR is required for proper expression of RPP4 during plant defense, thus linking the responsiveness of ATCOPIA93 to biotic stress and the co-option of its LTR for plant immunity. I will also introduce the two major follow-up projects that we are currently working on : 1) the identification and characterization of the transcription factors associated with ATCOPIA93 LTR which should allow us to study their interference with the epigenetic and hormonal pathways controlling this TE 2) the extent to which Polycomb is involved in the genome-wide silencing of TEs.
    Contact : BETERMIER Mireille <Mireille.BETERMIER i2bc.paris-saclay.fr>

    Lieu : Bibliothèque Bât. 34 - Campus de Gif-sur-Yvette

    Notes de dernières minutes :  !!CHANGE OF TIME AND LOCATION !! This seminar exceptionally starts at 10h00 so that you can go to the I2BC BBQ at Orsay (Bat 400) after the seminar

    En savoir plus : Département Biologie des Génomes
  • Département Biologie des Génomes

    Vendredi 22 juin 14:00-16:00 - Dr Alberto Vianelli - University of Varese (Italy) (sabbatical ENS, Paris)

    Overlapping genes in viruses and the de novo origin of proteins

    Résumé : This talk will focus on a genomic feature which looks at first as very specialized, but that in fact might be of general biological interest for different reasons, constituting a fascinating evolutionary puzzle and also possibly shedding some light on the still unsolved problem of the origin of novelty, namely new proteins : overlapping genes (OG) (gènes chevauchants). These are genomic regions of DNA or RNA (in the case of many viruses) which are translated in two (sometimes even three) reading frames to yield two proteins whose amino acid sequence, hence generally their function, is unrelated. It is thought they originate by “overprinting”, in which point mutations in an existing frame allow the expression of a completely new protein from the second frame. In viruses, in which OG are abundant, these new proteins often play a critical role in infection, yet they are frequently overlooked when annotating genomes. Their correct detection is however very important not only when studying viruses since they are now thought to be abundant in eukaryotes as well, with more and more examples being reported in the literature. As noted above, OG are evolutionarily puzzling since each of the two overlapping proteins constrains the freedom to change of the other. To conduct systematic evolutionary studies and to develop better detection methods, we have assembled a high-quality dataset of 80 non-homologous viral OG whose expression is experimentally proven. This allowed us to single out compositional features, that we show to be shared by proven mammalian OG as well, significantly different from non-overlapping genomic regions. We believe these and other features I will describe are relevant for understanding their evolution and their involvement in de novo protein origin not only in viruses. It is likely, in fact, that the new findings on eukaryotic overlapping genes mentioned earlier will eventually have a deep impact on our current vision of genes.

    Lieu : Salle E. Lederer - Bâtiment 430 - Campus d’Orsay

    Notes de dernières minutes : Time and location are exceptionnal : This seminar will take place at Orsay, Bât. 430 at 2 p.m.

    En savoir plus : Département Biologie des Génomes