Missions

Chlorophyll fluorescence is a powerful technique for studying plant physiology and the functional architecture of the light-harvesting apparatus. It is used in vivo and on isolated complexes or membranes, ranging from the scale of a single cell to remote sensing from space. These measurements span timescales from picoseconds to seasons and are indispensable for scientists, farmers, and policymakers.
A specific subset of these measurements can be done to obtain the rate of Photosystem II light harvesting. In the so-called fluorescence-DCMU curves, the sample is poisoned in darkness with DCMU, and the fluorescence kinetics on millisecond timescales are recorded upon the onset of illumination. On the thylakoid membrane level, PSII reaction centers are therefore allowed to perform only one charge separation before they reach their closed state and reach their maximum yield of fluorescence.
The kinetics of these fluorescence curves is sigmoidal, interpreted since the 1960s as an effect of energetic connectivity between chlorophyll molecules linking photochemical traps. However, several observations using chlorophyll fluorescence kinetics remain unexplained. Various theories have been proposed to explain these observations, including a distribution of antenna sizes between PSII supercomplexes, the presence of two photochemical traps in PSII with variable rates, and large variations in chlorophyll fluorescence yield in already-closed RCs.
We hypothesize a new theory, consistent with a number of observables and including the classic interpretation of connectivity. The goal of the project will be to test our hypothesis using a membrane-scale model of excitation energy transfer (EET). We need to vary the antenna concentration, static quenching rate, parameters of PSII charge separation (including a combination of photochemical and thermal variations of the fluorescence yield); and factor in the temporal dependence of the system upon the progressive closure of photochemical traps in the membrane.
Project Objectives:
In the short term, the first modeling objective will be to explain the curvature of DCMU curves using a membrane-scale model of fluorescence. Implementing these models will require developing and testing a range of membrane-scale models of photosynthetic light harvesting that include a variety of alternative pathways. Kinetic parameters for the models will be fit against a variety of different measurements available experimentally. One key challenge will be translating the physical models proposed into mathematical descriptions within the membrane-scale model. The modeling work will be accomplished in collaboration with the MesoScience Lab at the University of Texas at Austin.

Activités

Activities include:
• Development, evaluation, and validation of modeling algorithms.
• Development of datasets combining experimental data and models.
• Integration of observations into simulation models.
• Analysis of data contributions at the mesoscale.
• Production of specific simulations to meet project needs.
• Scientific collaborations with French and international collaborators

Compétences

Technical and Scientific Skills:
• PhD in one of the following fields: biophysics, biochemistry, modeling of biological systems, or related field.
• Strong knowledge of scientific programming (Python, MATLAB, etc.).
• Interest in transdisciplinary projects between experimental observations and modeling is valued.
• Scientific communication skills (written and oral) in English are essential.
Other Skills:
• Good organizational skills.
• Ability to work in a team.

Contexte de travail

The laboratory is located in Paris and offers a multidisciplinary environment with world-class experimental facilities and a substantial theoretical base for modeling work. The recruited researcher will join the team responsible for analyzing the variability of biological systems and will work closely with the MesoScience Lab at the University of Texas at Austin.

Contraintes et risques

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Informations complémentaires

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