Fig. 4

Red light-activated systems. a Near-infrared light is detected by BphG1 which triggers the release of GMP and secondary messenger c-di-GMP. The c-di-GMP is recognized by STING and activates the phosphorylation of IRF3 by TBK1. IRF3 then translocates into the nucleus, binds to IRF3-specific operators and induces the IFN controlled promoters. b PhyB/PIF system is activated by 650 nm and deactivated by 750 nm. In this split system, PhyB component is bound to the membrane, while PIF3 is in the cytoplasm. Light activation results in the dimerization of PhyB/PIF and the translocation of PIF-bound protein of interest to the nucleus. c The system incorporates VP16 and the Tet operon with PhyB and PIF. In the TetR-PIF6 split transcription factor construct, the N-terminal fragment of nuclear-targeted PhyB is fused to the VP16 TA domain, and the N-terminal of PIF6—to the tetracycline repressor TetR. To control expression of the gene of interest, the TetR-specific operator, TetO, is inserted into its promoter. Illumination with 650 nm light leads to the reversible heterodimerization of PhyB with PIF6. Since PhyB is fused to TetR, heterodimerization brings VP16 in vicinity of TetO, initiating transcription of the gene of interest. After far-red (740 nm) light-induced conversion of PhyB into its inactive form, the dissociation of PhyB-PIF6 inhibits expression of the transgene. BphG1 Rhodobacter sphaeroides phytochrome BphG1; GMP Guanosine monophosphate; GTP Guanosine triphosphate; c-di-GMP cyclic diguanylate monophosphate; STING stimulator of interferon genes; IRF3 interferon regulatory factor 3; TBK1 tank-binding kinase 1; DGCL diguanylate cyclase; ER endoplasmic reticulum; PINF(ACD +) interferon promoter; Phy phytochrome; PIF phytochrome-interacting factor; TetO tetracycline operator; tetR tetracycline repressor; VP16 activation domain of transcription factor VP16; PIF16 phytochrome interacting factor 16; PhyBFR active FR form of phytochrome B; Pol II polymerase II; goi gene of interest