biostudies-literatureJia HNational Natural Science Foundation of ChinaNational Natural Science Foundation of China (National Science Foundation of China)51https://www.ebi.ac.uk/biostudies/studies/S-EPMC12098889biostudies-literatureUnknown11(1)The red/far-red light receptor phytochrome B (phyB) plays essential roles in regulating various plant development processes. PhyB exists in two distinct photoreversible forms: the inactive Pr form and the active Pfr form. phyB-Pfr binds phytochrome-interacting factors (PIFs) to transduce red light signals. Here, we determined the cryo-electron microscopy (cryo-EM) structures of the photoactivated phyB-Pfr‒PIF6 complex, the constitutively active mutant phyB^Y276H‒PIF6 complex, and the truncated phyBN^Y276H‒PIF6 complex. In these structures, two parallel phyB-Pfr molecules interact with one PIF6 molecule. Red light-triggered rotation of the PΦB D-ring leads to the conversion of hairpin loops into α helices and the "head-to-head" reassembly of phyB-Pfr N-terminal photosensCell discoveryStructural insight into PIF6-mediated red light signal transduction of plant phytochrome B.PMC120988893240020532071211Liu ZGuan ZZhang DMa LZhu YJia HYin PTian DWang XDing JfalseStructural insight into PIF6-mediated red light signal transduction of plant phytochrome B.The red/far-red light receptor phytochrome B (phyB) plays essential roles in regulating various plant development processes. PhyB exists in two distinct photoreversible forms: the inactive Pr form and the active Pfr form. phyB-Pfr binds phytochrome-interacting factors (PIFs) to transduce red light signals. Here, we determined the cryo-electron microscopy (cryo-EM) structures of the photoactivated phyB-Pfr‒PIF6 complex, the constitutively active mutant phyB^Y276H‒PIF6 complex, and the truncated phyBN^Y276H‒PIF6 complex. In these structures, two parallel phyB-Pfr molecules interact with one PIF6 molecule. Red light-triggered rotation of the PΦB D-ring leads to the conversion of hairpin loops into α helices and the "head-to-head" reassembly of phyB-Pfr N-terminal photosens2025-01-01T00:00:00Z2025 May2026-06-02T20:46:27.171Z2026-04-20T03:10:59.442ZS-EPMC120988894040464110.1038/s41421-025-00802-3