The organelles of photosynthesis — the chloroplasts — have their own DNA, messenger RNA and ribosomes for forming proteins. Scientists have now discovered how to regulate the formation of proteins in the chloroplasts. They can use so-called riboswitches to switch the genes in the chloroplasts of tobacco plants on and off. These riboswitches could provide future benefit by making plants capable of delivering drugs or raw materials, or by improving the biological safety of genetically modified plants.