The chloroplasts of plants and algae evolved through endosymbiotic incorporation of a cyanobacterium. Few of hypotheses as to the molecular mechanisms underpinning endosymbiosis have been subject to direct experimental testing. We propose here the experimental recapitulation of the origin of plastids through endosymbiosis. A central aim is testing the hypothesis that the objective of the endosymbiont is maximising metabolic cooperativity under spatial constraints. We will test this hypothesis by genetic engineering of cyanobacteria and establishment of a synthetic cytosol-like environment in microfluidics devices.