F1F0-ATP synthases are multiprotein complexes, which are found in all living organisms. They meet the cellular demand for ATP and maintain ion gradients across membranes by an ion-flux-dependent, reversible ATP synthesis/hydrolysis reaction. Bacterial, mitochondrial and chloroplast F1F0-ATP synthases share the same core structure: a soluble F1 domain responsible for reversible ATP generation is connected by two stalks to the ion-translocating membrane domain. Correct assembly of F1F0-ATP synthases depends on multiple, intertwined cellular processes, and is even more challenging in eukaryotic organelles, since here – in addition to tight regulation of subunit transcription and translation – coordination of organellar import processes and two protein synthesis machineries is essential. Thus, biogenesis of F1Fo-ATP synthases requires the intervention of auxiliary factors, which carry out specialized functions in this highly concerted process.
In a search for novel photosynthesis-relevant factors in Arabidopsis thaliana, proteins were considered that are shared by photosynthetic eukaryotes from the green lineage but that are not found in non-photosynthetic eukaryotes. Those proteins are called GreenCut proteins and are likely to be associated with chloroplast functions. Knockout mutant lines were isolated and analyzed with respect to photosynthetic perturbations using a chlorophyll fluorescence screening procedure. As a result, we could identify two GreenCut proteins, which are specifically required for chloroplast F1F0-ATP synthase accumulation and provided evidence that they are involved in chloroplast F1F0-ATP synthase assembly.