Figure 1. Different strategies for optogenetic inputs.

Optogenetically stimulated signals can be induced in various ways (the photosensitive proteins that have been used for each approach are listed). System reversion occurs either in the dark or can be stimulated with light depending on the system used (BOX 1). a | Heterodimerization is used to recruit a signalling domain to its substrate, which is commonly located on the plasma membrane. b | Homodimerization and heterodimerization techniques recruit transcriptional activators or other DNA-modifying proteins to the DNA to initiate the expression of a gene of interest. c | CRYPTOCHROME 2 (CRY2) naturally clusters when it is activated. By fusing CRY2 with signalling domains, the activities of which depend on domain density, signalling can be activated with light. d | Alternatively, signalling can be inhibited by sequestering a signalling protein away from its site of action. Proteins can be sequestered in cytosolic clusters or recruited to compartments away from their downstream effectors or upstream activators. e | Conformational changes in the photosensitive protein can expose a concealed signalling domain or relieve a protein from an allosterically autoinhibited state. LOV, light-oxygen-voltage; PHYB, PHYTOCHROME B. Curvy arrows indicate the response of the system to light, whereas straight arrows indicate dark- or light-stimulated reversion. The small arrow on the DNA represents active transcription.