CE20 - Biologie des animaux, des organismes photosynthétiques et des microorganismes

Revelation of Acclimation Mechanisms of Photosynthesis using a Translational Approach in Evolutionary-distant Organisms – RevelOrg

Submission summary

Oxygenic photosynthesis is the earth’s lung. At the very base of this energetic process there are two photosystems (PSI and II) that absorb light energy and convert it into chemical energy that ultimately drives the life of a large part of the biosphere. Structure and function of the photosystems and their arrangement in the thylakoid membrane are constantly adjusting to changes in their environment, especially light, and regulatory mechanisms allows them to maintain performance and to cope with environmental stresses. Acclimation is the process by which a living organism is able to change and thrive when challenged by a new environmental condition. The sum of acclimation mechanisms that an organism has at its disposal contributes to the adaptation of a species. Understanding these biological processes is fundamental to our comprehension of ecology and evolution, to understand the challenge of stress in a climate change context and to the future improvement of CO2 capture by photosynthetic organisms. We want to use the differences and similarities between oxygenic photosynthetic organisms to get to the very heart of the molecular function of a carefully identified set of proteins that have important phenotypes in light acclimation. For this purpose, we will use a combination of in vivo and in vitro approaches to study the light acclimation mechanism in a model cyanobacterium, Synechocystis PCC6803, a prokaryote with a small genome; in a eukaryotic, green alga model, Chlamydomonas reinhardtii, and in the more complex model higher plant, Arabidopsis thaliana, in a parallel and tightly coordinated way.
We have discovered, using a high-throughput forward genetics approach, a cluster of new players in photosynthetic acclimation. Attesting to their physiological importance, Acclimation of Photosynthesis to the Environment 1 (APE1) and Thylakoid Lumenal Protein 15.2 (TLP15.2) have been conserved across all oxygenic photosynthetic organisms from cyanobacteria to higher plants. A third actor, Conserved in the Green Lineage 11 (CGL11) is a link to revealing the molecular mechanisms of photosynthetic control and cyclic electron flow that our analysis links to the well-studied PGR5. We have made important conceptual advances in understanding the basic function of APE1 in Chlamydmonas. APE1 is the first actor identified whose primary function is to bind to PSII supercomplexes and to release core complexes from interactions with light harvesting antenna in line with light intensity. This protects PSII from overexcitation in high light and promotes PSII heterogeneity, a function that influences the stacking of thylakoids. Furthermore it allows for PSII repair and turnover to increase with light intensity. We have begun preliminary work on APE1 in Arabidopsis. Here we propose to studying APE1 in Synechocystis, that will allow us to rapidly unearth its most fundamental function in photosynthesis. The acclimation mechanisms of PSII regulation and photosynthetic control are linked and are at the basis of acclimation to light in photosynthetic organisms but they have rarely been studied using genetic and biochemical means in parallel organisms at the same time. RevelOrg is a project which brings togther a group of researchers with vast knowledge in photosynthesis and genetics, molecular, biochemical and biophysical techniques to draw up a concerted model for light acclimation. In solving the biochemical mechanisms of APE1, TLP15.2 and CGL11 we can also explore the significant changes that exist on a regulatory (acclimation) level between photosynthetic organisms that have allowed them to thrive in salt water, fresh water or terrestrial habitats.

Project coordination

Xenie Johnson (Institut de biosciences et biotechnologies d'Aix-Marseille (UMR 7265))

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

I2BC Institut de Biologie Intégrative de la Cellule
BIAM Institut de biosciences et biotechnologies d'Aix-Marseille (UMR 7265)
BIAM Institut de biosciences et biotechnologies d'Aix-Marseille (UMR 7265)

Help of the ANR 554,159 euros
Beginning and duration of the scientific project: December 2020 - 48 Months

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