Figure 3.

Present models of phytochrome-mediated transcriptional regulation. (a) Phytochromes interact with transcription factors (e.g., PIFs) to sequester or block their DNA-binding domain to inhibit downstream gene expression. (b) Phytochromes interact with transcription factors such as PIFs and regulate their transcriptional activities with the aid of coregulators. (c) Light triggers interactions between photoreceptors and Aux/IAA, interfering with the auxin-induced degradation of Aux/IAA by the E3 ligase SCF^TIR and thereby promoting ARF activity and related auxin signaling. (d) Phytochromes interact with transcriptional activators, such as TZP, and enhance their transcriptional activity. (e) Light-signaling-related transcription factors recruit chromatin-remodeling proteins and histone-modifying factors to regulate light-responsive gene expression. It is not known how photoreceptors regulate this recruitment. The histone-modifying factors establish or read histone marks at the chromatin, whereas the chromatin remodelers alter histone-DNA contacts, leading to a new state, with the binding of light-signaling-related transcription factors occurring at light-responsive elements. Abbreviations: FT, FLOWERING TIME; phy, phytochrome; TF, transcription factor.