Bioscience and Biotechnology Institute of Aix-Marseille
Mechanisms of Stress Signalling by the Conserved (p)ppGpp Regulatory Cascade in the Chloroplast
Coordinator / LGBP contact : Ben Field
The stringent response is a conserved signalling cascade in prokaryotes that is orchestrated by the nucleotides guanosine pentaphosphate and tetraphosphate (together referred to as G4P). Conserved enzymes necessary for a stringent-like response are also found in photosynthetic eukaryotes due to the cyanobacterial ancestry of the chloroplast. In bacteria, G4P plays a pleiotropic regulatory role in coordinating growth in response to environmental stress. G4P represses macromolecular synthesis pathways involved in proliferation (protein, RNA/DNA, and lipid synthesis), and activates stress responses. In plants, G4P has been detected and G4P synthesis enzymes (RSH for RelA/SpoT Homolog) are localized in the chloroplast. We recently showed that in Arabidopsis G4P is a potent inhibitor of chloroplast gene expression in vivo, and that RSH enzymes regulate G4P homeostasis to control chloroplast function and influence plant growth and development. However, we still know very little about how RSH enzymes are regulated, the identity of the chloroplastic targets of G4P, the role of G4P during stress, or how the G4P signalling cascade works in diverse photosynthetic eukaryotes. The objectives of the proposed project are to: 1. Decipher the molecular mechanisms and regulation of G4P synthesis in the chloroplast of plants and microalgae. 2. Understand the role of G4P in controlling chloroplast function and stress acclimation. We will use innovative molecular genetic, biochemical, and 'omic approaches to address these aims in the two representative model organisms Arabidopsis and Chlamydomonas. It is of high importance to study growth and stress signalling pathways in plants and algae because together these organisms are responsible for ~75% of planetary primary productivity, and are key to the provision of ecosystem services and a food and fuel supply to humankind.
Regulation of the
TOR Signaling Pathway
Coordinator : Dr Lyuba Ryabova, CNRS, IBMP, Strasbourg
Plants, as immobile organisms, have a strong need to continually monitor environmental changes to transduce them into extensive transcriptional and translational changes that stimulate responses for adaptation and growth. A key-signaling pathway connecting environmental perception to growth decisions is the TOR (Target Of Rapamycin) pathway. TOR is a large protein kinase that acts in many cellular processes, controlling responses to growth factors, nutrients, energy and hormones. Plants seem to be also dependent on signal perception by TOR, but signals that act
via TOR are either not known or not characterized. The main objective is to determine the role of TOR signaling in multi-level adaptation of plants to environmental inputs such as light/ light stress and two growth and proliferation-related hormones auxin and cytokinin. We will also search for intermediates that link upstream TOR effectors with TOR activation using a combination of biochemical, genetic and pharmacological methods.
Water photolysis by Photosystem II studied by far-infrared spectroscopy
Coordinator / LGBP contact : Pr. Rainer Hienerwadel
Solar-driven hydrogen production from the abundant and cheap electron source water is a promising way to produce renewable energy. Nature-inspired solar converting systems need precise understanding of how Photosystem II tunes the properties of the Mn4CaO5 cluster to allow concerted electron and proton transfer and optimizes the challenging water oxidation process. We will use Photosystem II from the thermophilic cyanobacterium
Thermosynechoccocus elongatus prepared in specific biochemical and experimental conditions to probe light-induced transitions and spin conversion at the Mn4CaO5 cluster. Using state-of-the-art far-infrared FTIR difference spectroscopy notably at the AILES beamline of the synchrotron SOLEIL until 10 cm-1, we will specifically probe structural changes of the Mn4CaO5 cluster, the catalytic site for water splitting, and changes in structural and substrate water molecules with the goal to experimentally establish a mechanistic scheme for water oxidation.
External partners :
Manipulating energy signaling to improve biofuel production in photosynthetic eukaryotes
Coordinator / LGBP contact : Dr Benoît Menand, LGBP
One of the most promising alternative energy solutions is the use of microalgae like diatoms to produce biofuels, particularly lipids, by converting solar energy. However, the highest concentrations of lipids (triacylglycerol: TAG) are obtained during starvation, but this results in growth arrest and limits overall yield. The rationale of SIGNAUX_BIONRJ is that the manipulation of stress and energy signaling pathways could increase TAG content without compromising growth. We aim to generate fundamental knowledge on how two major stress and energy signaling pathways integrate signals from the chloroplast and the cytosol in order to regulate the balance between growth and TAG accumulation. The three partners of this project will combine expertise on signaling, microalgae, lipid metabolism, enzymology and transcriptomic.
Signaling of light-induced oxidative stress in the acclimation mechanisms of plants to climatic changes
Coordinator : Dr Michel Havaux, CEA, UMR7265 CNRS/CEA/Aix-Marseille Université
Most environmental constraints determining plant distribution on Earth and leading to crop yield losses culminate in an oxidative stress due to photosynthesis inhibition and accumulation of reactive oxygen species, especially singlet oxygen (1O2). Acclimation to
1O2 is of prime importance for the survival of photosynthetic organisms under natural environments. The main goal of this project is to elucidate the molecular mechanisms leading to this acclimation to predict the likely behavior of plants under climatic stress. The project combine complementary approaches to provide an integrated view of oxidative stress acclimation from the
1O2-production sites and the derived signals in the chloroplasts to the regulation sites at transcriptional and post-transcriptional levels in the cytosol and the nucleus, which collectively control the genetic reprogramming specific to the acclimatory response and the enhanced tolerance to subsequent stress.
Contact in LGBP : Dr Christophe Laloi
Photosystem structure and plasticity in response to the environment in plants and algae, a key to understand and improve growth
Coordinator / LGBP contact : Dr Stefano Caffarri
One of the biggest scientific challenges is to exploit solar energy in a better and more efficient way. Photosynthetic organisms perform the essential function of converting light energy into chemical energy thanks to flexible protein complexes located in the chloroplast membranes. We propose to investigate the molecular mechanisms necessary to remodel and regulate the structure and activity of photosystems in order to respond to environmental stresses. By a multidisciplinary approach, integrating membrane protein biochemistry, spectroscopy and physiology, the project will improve knowledge in the photosynthesis field and in particular on the structure-function-regulation of photosystems.
The plant TOR pathway: impact on translation in physiology and pathology
Coordinator / LGBP contact : Pr Christophe Robaglia
The main objective is to determine the role of the TOR pathway in the control of translation and ribosome biogenesis in normal and stressed conditions and to integrate it with our knowledge of the adaptation of plants to abiotic and biotic stresses. We will identify and investigate targets of the TOR pathway in the translational machinery. This project also includes the study of a viral protein that triggers reinitiation of mRNA translation and recruits the TOR protein. We will then investigate the connection between the TOR pathway and the phytohormones abscisic acid and salicylic acid, which are involved in stress responses.
Manipulating energy signaling to improve biofuel production in photosynthetic eukaryotes
Coordinator / LGBP contact : Dr Ben Field and Dr Benoît Menand
Photosynthetic organisms can be used to produce lipid-based biofuels as an alternative to fossil fuels. Starvation is required to stimulate the production of high quantities of lipids, but this also limits growth and the final lipid yield. In SIGNAUX-BIONRJ we are investigating how two major energy signaling pathways, the guanosine tetra phosphate pathway in the chloroplast and the TOR kinase pathway in the cytosol, can be modulated to improve the conversion of light energy into lipids and other energy storage compounds.
External partners : Dr Yonghua Li-Beisson, CEA, UMR7265
CHromatin and ROS: Role of topoisomerase VI in the transcriptional response of plants to singlet oxygen and other reactive oxygen species under abiotic stress
Coordinator / LGBP contact : Dr Christophe Laloi
The CHROS project is aimed at identifying the molecular mechanisms of the plant response to adverse environmental conditions, with particular emphasis on chromatin level control of gene expression in response to reactive oxygen species (ROS), as the production of ROS is a common feature of most abiotic stresses. More specifically, the CHROS project focuses on the elucidation of the mechanisms by which the plant topoisomerase VI and associated chromatin factors mediate stress-related gene expression changes in response to oxidative and abiotic stresses.
Chloroplast directed environmental stress acclimation in plants
Coordinator / LGBP contact : Dr Ben Field
The chloroplast is an essential organelle that is the site of photosynthesis in green plants and algae. The chloroplast was formed more than a billion years ago when a eukaryotic cell engulfed a photosynthetic bacterium. Remarkably several important bacterial stress-signalling pathways are still present in the chloroplast. In CHLORO_SAP we seek to understand the role of these ancient bacterial pathways in modern plants.
Evolution of the integration between environment and development in land plant
Coordinator / LGBP contact : Dr Benoît Menand
In order to determine the network of molecular mechanisms that integrate environment sensing and growth and development of plants and to understand how these mechanisms have evolved through land plant evolution, ENVI-DEVO study the TOR pathway in the moss
Physcomitrella patens which belongs to a very basal group of land plants.
Metalloproteins involved in oxidative stress defense studied by Far-IR Terahertz spectroscopy and theoretical methods
Coordinator : Dr Catherine Berthomieu
The aim of this project is to develop the use of far-infrared difference spectroscopy to provide key answers in the understanding of metal site properties in metalloproteins, in particular for SOD and SOR involved in the protection against oxidative stress. An important part of the project include technical and theoretical modeling developments to optimize measuring cells for at-home spectrometers and for the Far-IR synchrotron beam line at SOLEIL and to set a methodology for the normal mode prediction of optimized metal-active site structures.
External partners: Synchrotron SOLEIL, CEA, Saclay Contact in LGBP : Pr Rainer Hienerwadel
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.