Description du sujet de thèse

Rubisco plays a key role in the fixation of inorganic carbon during photosynthesis, literally “feeding life on Earth”. Being limiting in carbon fixation, Rubisco is a target to increase the productivity of phototrophs in the context of climate change. A wide variety of approaches are currently implemented to reach this goal, all of which require detailed knowledge of Rubisco expression, regulation and assembly. This thesis project aims to determine what controls Rubisco accumulation levels in vivo using the model microalga Chlamydomonas reinhardtii.

In green algae, Rubisco consists of an hetero-oligomeric LS8SS8 complex. The LS is encoded by the chloroplast rbcL gene and SS by two nuclear RbcS genes. Assembly of the complex requires a large number of auxiliary proteins, including the CPN60/20/10 chaperonins as well as specific assembly factors. Chaperonins and assembly factors enable LS to acquire its native conformation, and to oligomerize into a dimer and octamer capped by four SS at the apex and base. Homologues of conserved factors in plants and/or cyanobacteria are found in green alga, and consist of the RAF1, RBCX, and RAF2 chaperones, whereas the land plant-specific factor BSD2 is absent. A main objective of the project is to better characterize the factors required for Rubisco assembly in green algae, using Chlamydomonas reinhardtii as a model system. Open questions to tackle are i) whether and to which extend the RAF1 and RbcX chaperones are functionally redundant, ii) understand the molecular basis of RAF2 requirement, and iii) determine whether additional uncharacterized proteins found in the RAF1 play a role in Rubisco assembly in both mixotrophic and phototrophic conditions.
Furthermore, Rubisco overexpression in plants has been linked in some cases to enhanced yield. Improving algal productivity is also desirable, given their importance as feedstock and in the production of high-value compounds. Chlamydomonas strains overexpressing Rubisco will be engineered in order to test the functional consequences on photorespiration and pyrenoid structure and determine whether this translates in an increased biomass.

Contexte de travail

The Institute of Physical and Chemical Biology (IBPC), founded in 1930 by the Edmond de Rothschild Foundation, is dedicated to multidisciplinary research in all fields of biology. The structural, genetic and physico-chemical bases of living organisms are explored at different levels of integration, from molecules to entire organisms. The PhD student will join the 'Chloroplast Biology and Light Perception in Microalgae' laboratory (UMR7141) headed by Dr Angela Falciatore. It has around twenty permanent members (researchers, teacher-researchers, engineers, technicians and administrative staff) and around fifteen temporary collaborators, doctoral students and post-doctoral researchers. This laboratory, dedicated to the study of light-induced processes (photosynthesis and photoperception) and chloroplast biology, addresses key questions in biology, evolution and ecology of microalgae, focusing on different model organisms (Chlamydomonas reinhardtii and diatoms) and ecologically important phytoplankton species, studied using ecophysiological, biophysical, biochemical, genomic and genetic approaches. The thesis work will be carried out under the direction of Alix Boulouis and under the supervision of Katia Wostrikoff at UMR7141 at IBPC, and may occasionally be conducted at the partner laboratory at BIAM in Marseille involved in the ANR RubExCES.

Contraintes et risques

The project involves handling radioactivity under controlled conditions.

Informations complémentaires

The doctoral contract is funded by ANR RubExCES (2025-2028) for a period of three years. The position is available from 10 October 2025. Applications must be submitted via this interface and must include a CV and a cover letter summarising the candidate's scientific interests.