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Chloroplasts are plant organelles responsible for the bulk of terrestrial photosynthetic primary production. They evolved via endosymbiosis from a cyanobacterial organism more than a billion years ago. The biogenesis and operation of chloroplasts depends on the assembly and homeostasis of thousands of nucleus-encoded proteins, which together constitute a large part of the organellar proteome. These proteins are imported by multiprotein translocases in each of the chloroplast envelope membranes after translation in the cytosol. Chloroplast proteins are subject to proteolytic regulation, which plays vital roles in maintaining normal organellar functions and in delivering responses to developmental and environmental cues. Turnover of internal chloroplast proteins is controlled by proteases inherited from the organelle’s prokaryotic ancestor, but mechanisms underlying the degradation of …