L’équipe propose des sujets de Thèse :
- Etude de la signalisation MAPK en réponse aux stress (a)biotiques à l’aide de lignées exprimant des formes constitutivement actives de MAPKs.
Responsable : Julien Lang
- Caractérisation in vivo de la dynamique de signalisation MAPK activée par les stress à l’aide de senseurs protéiques fluorescents et de la microfluidique.
Responsable : Jean Colcombet
- Etude de la régulation post-traductionnelle du module MEKK1-MKK1/MKK2-MPK4 chez Arabidopsis.
Responsable : Bénédicte Sturbois
Plants need to coordinate their internal processes to develop properly and adapt to the environmental constraints. Thereby they evolved various perception and signalling systems to coordinate their responses.
Phosphorylation/dephosphorylation processes controlled by protein kinases and phosphatases respectively are key steps of these signalling networks for an accurate and rapid response to a given signal. Strikingly, with more than 1000 genes (>3.3% of the total number of genes), protein kinases define the largest family encoded by plant genomes.
The laboratory aims to investigate the functions of important families of kinases during stress signalling and plant adaptation to environment.
Among eukaryotic kinases, Mitogen-Activated Protein Kinases (MAPKs) are evolutionary conserved serine/threonine protein kinases that transduce different extracellular signals to various cellular targets in animal and yeast. The activity of MAPKs is tightly regulated by dual phosphorylation on a well-conserved T-X-Y motif in their activation loops. This process is controlled by MAPK Kinases (MAPKKs) which are themselves activated by phosphorylation on a S-X3-5-S/T activation loop motif by the diverse family of MAPKK Kinases (MAPKKKs).
Thus the signal is transduced in the form of a phosphorylation cascade within the MAPK modules, from upstream kinases to the downstream MAPK. In most biological systems, the initiation of the MAPK cascades often involves membrane-located receptors and G-proteins. Cytosolic kinases and nuclear transcription factors are common targets of activated MAPKs.
Interestingly, the Arabidopsis genome codes for 20 MAPKs, 10 MAPKKs and 80-90 MAPKKKs, indicating a central role in plant signalling pathways. Several MAPKs, MAPKKs and MAPKKKs have been studied in plants, defining various MAPK cascades involved in various processes. Similar to mammals, plant MAPK signalling is a highly complex process involving feed-back mechanisms and cross-talk between different pathways. Our work and others showed that a particular MAPK can be activated by various stimuli and a specific stimulus can activate different MAPKs. It is now clear that plant MAPK cascades are activated in response to abiotic and biotic stimuli, hormones and during developmental processes such as cell division and position-dependent cell differentiation. Our research is focused on MAPK cascades involved in adaptation to environmental constraints.
Plants also possess a large family of specific kinases, the Calcium Dependent Protein Kinases (CDPKs) able to bind the second messenger Calcium (Ca2+) to translate cytosolic Ca2+ variations into phosphorylation output. They were shown to regulate plant responses to both biotic and abiotic stresses, either independently or in coordination with MAPK modules.
Our first aim is to understand how signal specificity is maintained along the phosphorylation cascade. For example, we want to study the physical interactions between MAPKKKs, MAPKKs and MAPKs and also identify scaffold proteins involved in assembly and specificity of particular kinase complexes. Moreover, we aim to elucidate downstream events of signalling modules in terms of direct phosphorylation targets and consequent modulation of gene expression and epigenetic control at the genome level. To reach these objectives, the group developed several strategies such as the phenotypical and biochemical studies of kinase mutants as well as proteomic and phosphoproteomic studies to identify important targets and interactors of the kinases. We also developed a powerful genetic tool by expressing constitutively active kinases in planta to decipher their biological functions.