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. 2002 Nov;3(11):1042–1048. doi: 10.1093/embo-reports/kvf222

Figure 2.

Figure 2

A model of phytochrome signal transduction. Activated phytochrome (Pfr) is proposed to regulate transcription through several parallel pathways. A rapid response involves Pfr translocation to the nucleus, where it binds transcription factors of the bHLH family (in particular PIF3). Key regulatory transcription factors (RTFs) that are responsible for inducing a range of light-regulated genes are subsequently activated. In a second nuclear-localized pathway, phytochromes are proposed to bind response regulators (RR), which stabilize them in the activated form and can induce light-regulated gene expression by inhibiting COP1-, COP10- and CSN-dependent proteolysis of the HY5 transcription factor and by binding to activated cryptochromes (cry). In all cases, regulation of the genes responsible for photomorphogenesis is predicted to require chromatin remodelling mediated by the DET1/DDB1 nucleosome-binding complex. In the cytoplasm, phytochrome may activate gene expression through G-proteins (G), calcium and cGMP-dependent pathways, which are regulated by SUB1. In addition, phytochromes may be sequestered away from the signalling-competent pool by PKS1. Elements involved in signalling from specific photoreceptors or controlling specific responses have not been included.

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