Phytochrome B

Regulatory photoreceptor which exists in two forms that are reversibly interconvertible by light: the Pr form that absorbs maximally in the red region of the spectrum and the Pfr form that absorbs maximally in the far-red region. Photoconversion of Pr to Pfr induces an array of morphogenetic responses, whereas reconversion of Pfr to Pr cancels the induction of those responses. Pfr controls the expression of a number of nuclear genes including those encoding the small subunit of ribulose-bisphosphate carboxylase, chlorophyll A/B binding protein, protochlorophyllide reductase, rRNA, etc. It also controls the expression of its own gene(s) in a negative feedback fashion. Involved in the flowering time regulation. Involved in light-regulated circadian phase control that triggers stomatal aperture, stomatal conductance, and CO assimilation. Implicated in red light perception, and, to a lower extent, in blue light signaling (PubMed:12177480). Regulates temperature responses by associating with the promoters of key target genes in a temperature-dependent manner and subsequently repressing their expression probably in a PIF4-dependent manner. Thermal timer that integrates temperature information over the course of the night (PubMed:27789797).