Glutathione (gammaGlu-Cys-Gly, GSH) is a crucial metabolite in eukaryotes and many bacteria. In plants, glutathione deficiency leads to severe developmental defects. GSH binds covalently to diverse classes of endogenous or exogenous molecules. It can form a mixed-disulfide bond with protein cysteines, a redox post-translational modification termed S-glutathionylation which is favored under stress conditions. It can also be conjugated to electrophilic metabolites for the synthesis, recycling or intracellular distribution of specialized metabolites, reactions mainly catalyzed by glutathione transferases (GSTs). The Glutaclick project will address important but yet underexplored biological questions related to glutathione signaling and conjugation functions in a context of stress responses in the model photosynthetic eukaryote Chlamydomonas reinhardtii. This project will uncover the substrates of algal GSTs to unravel their specificities and thereby infer some of their functions. This project will have important repercussions in the way GSTs are studied notably by facilitating and clarifying their catalytic and functional role(s). GlutaClick will give also new insight into the importance and the role of S-glutathionylation in eukaryotes. By identifying a large set of target proteins including membrane proteins, an important class of proteins involved in crucial processes (bioenergetics, signaling, transport or intra/inter cellular communication), we expect to give a more complete picture of the processes under the control of this modification. The Glutaclick project will allow to define both the physiological conditions triggering this post-translational modification in vivo and how this modification is controlled and in particular by which glutaredoxins. It will also allow to analyze temporal and quantitative dynamics of the S-glutathionylation network and to unravel the underlying molecular mechanisms. Finally, qualitative and quantitative data will be used to initiate mathematical modelling of the glutathionylation network and identify key information about the chemical and physical features conferring glutathionylation specificity. We anticipate that many of the results obtained in the Glutaclick project will be relevant to other photosynthetic organisms. The data will therefore constitute a wealth of information for the plant scientist’s community and notably to initiate functional studies combining in vivo and in vitro approaches. Glutathione being found in most eukaryotes and many bacteria, the molecular mechanisms unraveled by our analyses will likely relevant to most signaling and conjugating functions of glutathione in both photosynthetic and non-photosynthetic organisms. Last but not least, this project will generate innovative chemical and biological tools that will be valuable for the scientific community to by-pass actual technological barriers limiting studies aiming at deciphering GSH roles.