Resolution achieved Chloroplasts possess multiple copies of their own chloroplast DNA that are packaged into DNA-protein complexes known as nucleoids. The shape, number, and distribution of chloroplast nucleoids change markedly depending on the cell cycle, developmental stage, and nutritional environment. Kobayashi et al. identified Holliday junction resolvase as a key factor in the dynamism of chloroplast nucleoids in the unicellular green algae Chlamydomonas reinhardtii . The gene encoding the resolvase is ubiquitously conserved among green plants. Disruption or down-regulation of this gene also disturbed chloroplast nucleoid organization and segregation in the land plant Arabidopsis thaliana . Science , this issue p. 631