Respiration is a key metabolic pathway providing ATP to fuel cellular functions. Cellular respiration is composed of three main pathways, the glycolysis, the TCA cycle and the oxidative phosphorylation (OXPHOS) system. The OXPHOS system uses the redox energy stored in cofactors by the glycolysis and the TCA cycle to create an electrochemical gradient across the mitochondrial inner membrane that will be used for ATP synthesis. The OXPHOS system is composed of five main complexes (complexes I to V) conserved from bacteria to higher eukaryotes. The OXPHOS system of plants contains additional enzymes that allow alternative routes for electrons. Besides, each of the complexes I to V contains plant-specific subunits. The roles of these plant specific features are not well understood. Our current research aims at resolving the composition, function and regulation of the OXPHOS system.

Complex I is the largest complex of the OXPHOS system and it contains subunits encoded by the mitochondrial and nuclear genomes. We use complex I as a model to study interactions between mitochondria and the rest of the cell (coordination of the assembly of subunits originating from two different compartments, regulation of metabolic fluxes by complex I activity).

Using bioinformatics analysis (Hansen et al 2018), we have built a list of complex I related genes, mostly encoding proteins of unknown functions. These proteins are candidate assembly or regulatory factors. Using reverse genetic approaches, we are currently investigating the role of these proteins.

Interestingly, some of the proteins we studied appear to be important for the formation of supercomplexes (stoichiometric assemblies of one or more OXPHOS complexes). Therefore, we are currently investigating the role(s) of respiratory complexes in plant mitochondria.

Using systems biology approaches, we are also studying the consequences of the absence of complex I on cellular metabolism. We have recently identified complex I as a negative regulator of respiratory fluxes in mutants of the model plant Arabidopsis thaliana (Kühn et al 2015) but also in the parasitic plant Viscum album (European mistletoe) that lost complex I (Maclean et al 2018). We are currently investigating the mechanisms involved in this regulatory role in both systems.