In the context of climate change, it appears essential to unravel the mechanisms governing abiotic stress tolerance in higher plants, in order to build predictive models and use this knowledge to assist selection and design of stress tolerant crops. We have previously uncovered remarkable adaptations in seed mitochondria, which because of the ability of seeds to survive desiccation, display impressive tolerance to abiotic stress. In particular, seed mitochondria accumulate high levels of small heat shock proteins (sHSP) and late embryogenesis abundant proteins (LEA). The sHSP are the most widespread but less conserved HSP. They contribute to the molecular chaperone network that assists protein biogenesis and homeostasis under stress conditions (sHSPs are stress inducible). In eukaryotes, mitochondrial sHSP (M-sHSP) have only been identified in plants and insects. LEA proteins are highly hydrophilic proteins, generally intrinsically disordered, which accumulate in desiccation tolerant organisms, and whose functions still remain largely enigmatic. The MITOZEN project aims at deciphering the molecular function and physiological role of the mitochondrial sHSP and LEA proteins (M-sHSP and M-LEA) in the model plant Arabidopsis thaliana. The genome of Arabidopsis harbors 17 sHSP genes (including 3 M-sHSP) and more that 50 LEA genes, among which we have recently identified 5 M-LEA genes. The molecular functions of the M-sHSP and M-LEA will be explored using biochemical and biophysical approaches to study recombinant proteins produced in Escherichia coli. Their structural features and protective activities (oligomerisation, secondary structure, chaperone activities, membrane protection) will be examined in the context of temperature stress and dehydration using a large panel of techniques and in vitro assays. The goal is to determine the potential molecular functions of the different M-sHSP and M-LEA in the context of stress tolerance (desiccation in seeds, high temperature in seeds and plants). A reverse genetics approach will be developed in Arabidopsis to explore the role of M-M-sHSPs and M-LEAs in the physiology and development of plants. Single and multiple knock-out mutant lines will be constructed, as well as overexpressors using an inducible system. Their phenotypic characterization will focus on seed development and abiotic stress tolerance of plants, including mitochondrial function. The integration of data provided by these multidisciplinary approaches (bioinformatics, biochemistry and biophysics, genetics, physiology) will shed light on the function and importance of the different M-sHSP and M-LEA in the development and stress tolerance of plants. It will also increase knowledge about molecular chaperones and in particular with respect to their yet unexplored role in the context of dehydration, and will shed novel light on the function of LEA proteins.