Phosphate (Pi) starvation is a frequent nutrient stress impacting crop yields. To adapt to this stress, plants exert different mechanisms to increase the uptake of extracellular Pi and to remobilize intracellular reserves. In cells, one third of the Pi is retained in phospholipids, the main components of extra-plastidial membranes. During Pi starvation, phospholipids are partially degraded to release Pi and are replaced by a non-phosphorous lipid synthesized in plastids: the digalactosyldiacylglycerol (DGDG). Thus, the synthesis and transfer of DGDG from plastids to other organelles is highly stimulated in this situation. However, the mechanisms involved in lipid remodeling remain poorly understood. DGDG transfer to mitochondria is thought to occur by non-vesicular pathways at contact sites between mitochondria and plastids. Recently, we have identified in Arabidopsis thaliana a super-complex, the MTL (Mitochondrial Transmembrane Lipoprotein) complex, involved in DGDG transfer to mitochondria during Pi starvation. Among this complex, AtMic60, a protein located in the inner membrane of mitochondria, plays an indirect role in DGDG transfer 1) by regulating contact sites formation between both mitochondrial membranes and 2) by destabilizing membranes. Only a partial decrease of DGDG transport is observed in the absence of AtMic60, suggesting that other pathways are also involved. In addition, we currently do not know how plastid-mitochondria contact sites, an important structure for lipid transport, are formed. The goal of the MiCoSLiT project is to identify keys actors involved in DGDG transport to mitochondria and/or in the formation of plastid-mitochondria contact sites in response to Pi deprivation. Our working hypothesis is that the MTL complex and other actors, which remain to be identified, are involved. First of all, a combination of three biochemical approaches will be optimized to identify new candidate proteins potentially involved in such processes. A first approach corresponds to a deep analysis of the composition and organization of the MTL complex in order 1) to better understand its functions and 2) to highlight new components putatively involved in lipid transport and/or membrane contact sites formation. Two non-targeted approaches, corresponding to the analysis of the mitochondrial proteome in response to Pi starvation and the optimization of a method to isolate plastid-mitochondria contact sites, will be performed in parallel to identify new pathways. All these approaches will be performed from A. thaliana cell cultures grown in presence and in absence of Pi to highlight candidates specifically involved in Pi-starvation response. Then, a functional analysis of a small subset of candidates will be undertaken to decipher their role(s) in the transport of lipids to mitochondria and/or in the formation of plastid-mitochondria contact sites. Finally, the involvement of these candidates in the global response of plant to Pi starvation will be studied in order to demonstrate the important role of lipid remodeling in the adaptation of plant to this situation. Impacts of the MiCoSLiT project are expected in both basic research and agricultural sciences. Indeed, the project will increase our understanding of the mechanisms involved in mitochondrial lipid transport and in the formation and regulation of contact sites between organelles, processes which remains poorly characterized, particularly in plants. In addition, by the investigation of the cellular mechanisms involved in plant response to Pi starvation, the project will open important perspectives in the development of crops presenting higher yield when grown in low-Pi soils.