Efficient energy metabolism is critical for plant growth and survival, especially under hypoxic conditions where oxygen availability is restricted. Cytochrome c oxidase (COX), the terminal enzyme of the electron transport chain, is needed for ATP production through oxidative phosphorylation in all eukaryotes. HIGD proteins, including yeast RCF1 and RCF2 and their mammalian homologs HIGD1A and HIGD2A, regulate COX activity, supporting cellular respiration in response to hypoxia and oxidative stress. These proteins remain bound to COX after assembly, modulating its function to sustain efficient respiration. In plants, early nodulin 93 (ENOD93) and HIGD1,2 and 3, are small mitochondrial proteins associated with nitrogen fixation, nitrogen use efficiency and hypoxia tolerance. But they each likely act in these processes as regulators of COX subunits in plants. ENOD93, homologous to the N-terminus of yeast Respiratory Supercomplex Factor 2 (RCF2), appears to affect proton translocation and the proton motive force (PMF) across the mitochondrial membrane, potentially altering COX structure and function. The role of HIGs in plants in less clear. This project investigates the evolutionary relationships between plant ENOD93 and HIGDs, mammalian HIGD proteins, and yeast Rcf2, as well as the functional interoperability of ENOD93 and HIGD proteins in plant mitochondria. Through structural predictions and complementation studies in Arabidopsis, we aim to characterize the roles of the ENOD93 gene family across crops to assess how enhanced mitochondrial ATP production during nitrogen-related processes is influenced by hypoxia and could lead to hypoxia tolerance and/or nutrient utilization efficiency.