By combining a riboswitch with a cell-permeable photocaged small molecule ligand, an optochemical gene control element was constructed, enabling spatial and temporal control of gene expression in bacterial cells. Because of the simplicity of this strategy, coupled with the ability to create synthetic riboswitches with tailored ligand specificities and output in a variety of microorganisms, plants, and fungi, this approach may afford a general strategy to photo-control gene expression in vivo. The ability to activate riboswitches using light enables the interrogation and manipulation of a wide range of biological processes with high precision, and will have broad utility in regulation of artificial genetic circuits.