. . . . "Chloroplastes" . "Chloroplaste" . "Text" . . . "Guanosine tetra-phosphate and penta-phosphate (ppGpp and pppGpp), which are synthesized/hydrolyzed by RelA/Spot homolog (RSH) enzymes, play a central role in the adaptation of bacteria to nutrient limitation or other stresses. Both RSH enzymes and ppGpp are present in the chloroplasts of plants. Recent studies have shown that ppGpp acts as a global repressor of chloroplast gene expression. Certain environmental stresses and hormones induce ppGpp accumulation in chloroplasts, however the molecular mechanisms underlying the activation of ppGpp signalling in response to such stimuli is essentially unknown. We searched for factors that interact with RSH enzymes and so could play a role in activating ppGpp signalling. Using a targeted yeast two hybrid screen several proteins were identified that interact with RSH enzymes including acyl carrier protein (ACP) and ribosome associated GTPases. ACP and RSH1 appear to be required for ppGpp induction in response to fatty acid biosynthesis depletion, while ppGpp and an RSH-interacting GTPase contribute to the resistance of plants to heat shock. We also performed non-targeted co-immunoprecipitation mass spectrometry (CoIP-MS) of RSH1. New RSH interaction candidates were identified, including plastid nucleoid associated proteins and chloroplast signalling proteins, suggesting that RSH1 may be associated with the plastid transcription machinery. Our results give new insights into ppGpp signalling, and show that some elements are conserved between plants and bacteria, while others are implicated in plant-specific biological processes." . "RelA-SpoT Homologues" . . . "Identification of factors regulating guanosine tetraphosphate (ppGpp) biosynthesis in Arabidopsis thaliana" . "Th\u00E8ses et \u00E9crits acad\u00E9miques" . . . "La ppGpp et la pppGpp, qui sont synth\u00E9tis\u00E9es/hydrolys\u00E9es par les RelA/Spot homologs (RSH), jouent un r\u00F4le centrale dans l\u2019adaptation des bact\u00E9ries contre la privation des nutriments et les stress environnementaux. Les enzymes RSH et ppGpp ont \u00E9t\u00E9 d\u00E9couverts dans le chloroplaste. Il a \u00E9t\u00E9 r\u00E9cemment d\u00E9montr\u00E9 que ppGpp joue un r\u00F4le comme r\u00E9presseur globale de l\u2019expression de g\u00E8nes chloroplastiques. Certains stresses environnementaux et hormones induisent l\u2019accumulation de ppGpp chez les plantes, cependant le m\u00E9canisme mol\u00E9culaire n\u2019est pas encore connu. Ici nous nous sommes int\u00E9ress\u00E9s \u00E0 d\u00E9couvrir les facteurs qui interagissent avec les RSH, et qui donc sont susceptible de r\u00E9guler le m\u00E9tabolisme du ppGpp. En utilisant un crible double-hybridation de levure nous avons identifi\u00E9es des proteines qui interagissent avec les RSH y compris l\u2019acyl carrier protein (ACP) et des GTPases associ\u00E9es au ribosome. ACP et RSH1 semblent \u00EAtre indispensables pour l\u2019accumulation de ppGpp induite par la carence de la biosynth\u00E8se des acides gras, tandis que le ppGpp et un GTPase associ\u00E9 au ribosome contribuent \u00E0 la r\u00E9sistance contre le heat-shock. Nous avons aussi effectu\u00E9 du co-immunopr\u00E9cipitation spectrom\u00E9trie de masse avec RSH1. Plusieurs prot\u00E9ines ont \u00E9t\u00E9 identifi\u00E9es y compris des prot\u00E9ines associ\u00E9es au nucl\u00E9oid et des prot\u00E9ines li\u00E9es \u00E0 la signalisation chloroplastique, indiquant que RSH1 pourrait etre impliqu\u00E9 dans la machinerie de transcription chloroplastique. Nos r\u00E9sultats montrent que chez les plantes le ppGpp joue un r\u00F4le non seulement comme chez les bacteri\u00E9s mais aussi participe \u00E0 de nombreux processus biologiques qui sont sp\u00E9cifiques aux plantes." . . "Identification of factors regulating guanosine tetraphosphate (ppGpp) biosynthesis in Arabidopsis thaliana" . "Enzymes v\u00E9g\u00E9tales" . "PpGpp" . "Arabidopsis thaliana" . "L'identification des facteurs qui modulent la biosynth\u00E8se de ppGpp chez Arabidopsis thaliana" . . . "2016" . . . . . .