Cells from higher plants and algae contain a compartment specific to the plant kingdom: the chloroplast. This organelle is the place of oxygen production and of synthesis of vitamins, amino acids, fatty acids, lipids, starch... i.e. most compounds essential for our diet and sources of bioenergy. To synthesize these molecules, the chloroplast only needs CO₂, water, minerals and some metals. The energy used to catalyze all these reactions derives from the conversion of solar energy into chemical energy through photosynthesis. However, the mechanisms that regulate dynamic exchanges between the chloroplast and other cell compartments still remain poorly understood.

Current estimates suggest that the chloroplast contains about 3500 different proteins catalyzing above-cited reactions. Variations in environmental conditions (light, temperature, etc.) perceived by plants require constant adaptations of the chloroplast composition to optimize its functioning. However, the vast majority of these 3500 proteins must be imported into the chloroplast by mechanisms that, for some of them, remain unknown. These mechanisms are themselves catalyzed by yet unidentified proteins located in two biological membranes (the envelope) that surround the chloroplast. As these envelope proteins are very rare at the chloroplast and plant cell scales, their identification required the use of cell fractionation (to enrich them, Figure) and proteomics approaches (to identify them). During this study, researchers ar IRIG combined biochemical, imaging, mass spectrometry, bioinformatics and statistical approaches to reveal previously unidentified protein components present in these membranes.