EXPLORING THE ROLE OF A NEW PLANT SPECIFIC WG/GW PROTEIN FAMILY IN RESPONSE TO HEAT STRESS AZEVEDO FAVORY Jacinthe1, ALART Emilie1. PICART Claire1, LAUDIE Michèle, PONTIER Dominique, VIGNOLS Florence3, HAKIMI Mohamed-Ali2, LAGRANGE Thierry1 1 Laboratoire Génomes et Développement des Plantes, UMR5096, CNRS/UPVD, Perpignan, FRANCE 2 Host-Pathogen Interactions and Immunity to Infections, Institute for Advanced Biosciences (IAB), UMR5309 INSERM/CNRS/Université Grenoble Alpes, Grenoble, FRANCE 3 Biochimie et Physiologie Moléculaire des Plantes, University of Montpellier, Centre National de la Recherche Scientifique, Institut National de la Recherche Agronomique, SupAgro, 34060 Montpellier, FRANCE Plants evolved to acquire sophisticated and specialized RNA silencing pathways, leading to sequence specific regulations through Argonaute effector proteins guided by small RNAs (sRNA), targeting either DNA or RNA. Our lab contributed to the development of an original aspect highlighting the existence of an evolutionary GW-rich conserved motif in factors implicated in AGO action, and defined as "Ago hook" proteins. In order to propose a systematic, cross-species approach to the identification of Ago-hook proteins, we developed a bioinformatic screen based on the presence of a GW/WG dipeptide in a compositionally-biased environment. Among candidates identified in A. thaliana, one protein family stands out from factors previously described. This new protein family, composed of two members, is conserved among angiosperms and presents no other known functional domain. Whereas first evidences confirm their AGO-hook properties, our last breakthroughs lead to us to reconsider their role at the crossroads of RNA silencing and abiotic stress regulation pathways, thereby raising many questions at this stage of our work.