Research Themes

Understanding how Photosynthesis Acclimates to the Environment

Motivated by the advancement of scientific knowledge, our research topics can meet potential needs in agronomy, ecology, plant breeding, bioenergy or green biotechnologies. Indeed, scientific expertise in integrated photosynthesis is needed to invent solutions for adaptation or mitigation to climate change, to understand the acclimation of plants and ecosystems to increased CO2 and temperature, and to better quantify the contributions of plants and microalgae to biogeochemical cycles.

ANR RevelOrg 2021-2025

This theme addresses the light acclimation process in photosynthetic organisms using molecular genetics and comparative phenotyping. The APE1 protein factor, as well as other light acclimation factors will be studied simultaneously in four model organisms (Arabidopsis, Chlamydomonas, Synechocystis and Synechococcus). To do so, we are working in collaboration between researchers with different skills in photosynthesis: work on Arabidopsis, biochemistry and microscopy will be led by Professor Stefano Caffari (BIAM/LGBP, BIAM). Corinne Cassier-Chauvat (CNRS, iB2C, Saclay) will lead the work on cyanobacteria and photosynthetic metabolism. This work will be enriched by a broader and more global “-omics” study of the stress response related to light acclimation. The coordinator, Xenie Johnson at BiAM will use biophysical measurements to characterize the physiological importance of these factors in the regulation of photosynthesis. At the heart of the project, the structure-function analysis of APE1 and the study of its molecular interactions will allow us to characterize a molecular mechanism that integrates different factors of light acclimation.

ANR PhotoRegul 2018-2022

State transitions, that allow changes to light absorption between the two photosystems without energy dissipation, are an important form of photoprotection. This works via phosphorylation of LHCII antenna by a kinase, Stt7. The mechanism of activation of Stt7 kinase by cytochrome b6f was poorly understood because knowledge indicated that the kinase domain of Stt7 was located on the stromal side of the membrane (Qi site) while the activation signal was thought to originate from the luminal side of the membrane (Qo site). Our recent advances in understanding this mechanism have allowed us to reveal that the triggering of Stt7 kinase to phosphorylate LHCII proteins occurs via a direct interaction with the cytochrome b6f complex in the stromal compartment (Dumas, 2017 & 2018). This discovery expands our horizons as we have now identified key residues of cyt b6f involved in the interaction with Stt7.

This project is currently continuing using the Phos-tag SDS PAGE technique to measure the phosphorylation status of the Stt7 protein kinase in various reference strains or strains affected by targeted mutations.

Regulation of stomatal pore opening is a key process that governs a “constitutive” trade-off that plants must face in nature: limiting water loss from day and night transpiration while allowing CO2 diffusion into the leaf for photosynthetic uptake. Despite the importance of night-time stomatal closure in maintaining plant health and limiting water losses in the ecosystem, it remains unclear whether this stomatal response to darkness is simply a passive consequence of the absence of light stimulus, or an active process recruiting other stomatal closure mechanisms or involving independent signalling events.

Using an IR imaging-based screen, we had isolated the ost2 mutant, (ost for open stomata) and a class of novel Arabidopsis mutants that keep stomata open all night long that we named opal for “open all night long” (Costa et al 2015). Based on their phenotypic responses to ABA and CO2, we proposed that these mutants are affected on specific regulations of stomatal closure in the dark. In other words, it is not only the lack of light that regulates stomatal closure in the dark. Genetic and molecular characterization of these mutants was undertaken. The characterization of opal2 led us to the identification of a molecular candidate involved in the chloroplastic carbon metabolism of the guard cell (work in progress). Furthermore, a collaboration with A. Hetherington (Bristol Univ., UK) on opal5 allowed us to confirm the key role of guard cell actin in the stomatal light/darkness response (Isner et al. 2017).

Furthermore, recent work undertaken on stomatal and transpiratory responses to light/darkness, ABA, CO2, and atmospheric water vapour deficit in different stomatal mutants and in different plant species, lead us to propose that water supply to different mesophyll tissues is regulated by the magnitude of the transpiration flux per se. In this context, we have worked on the development of new non-invasive tools based on THz spectroscopy that allow us to experimentally address the dynamics and distribution of hydration in mesophyll tissues.

How can we optimize photosynthesis to improve agricultural yields?

The CAPITALISE project aims to provide results leading to a sustainable environmental action plan in 2030. It aims to improve photosynthetic efficiency by 10% in different types of environments. Within the framework of CEA programs, we propose to identify original traits related to chlorophyll levels from mutant lines of tomato, barley and maize. These factors will allow to increase the efficiency of light use by optimizing chlorophyll levels based on the exploitation of natural variation. This work will be carried out in collaboration with Roberta Croce professor at Vrije Universitat d’Amsterdam in the Netherlands.

H2020 CAPITALISE Project: Combining Approaches For Photosynthetic Improvement To Allow Increased Sustainability In European agriculture

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