8f5z
From Proteopedia
Composite map of CryoEM structure of Arabidopsis thaliana phytochrome A
Structural highlights
FunctionPHYA_ARATH 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. Can phosphorylate FHY1 and, possibly, FHL, in red light conditions; this inactivates their co-shuttling to the nucleus (PubMed:19208901). Regulates phototropic responses both in the nucleus (e.g. hypocotyl elongation and cotyledon opening under high-irradiance conditions and seed germination under very-low-fluence conditions) and in the cytoplasm (e.g. negative gravitropism in blue light and red-enhanced phototropism) (PubMed:17566111). Promotes seed germination, suppression of hypocotyl elongation, and randomization of hypocotyl growth orientation in far-red light; these responses to far-red light are repressed by UNE10/PIF8 (PubMed:31732705). Stabilizes UNE10/PIF8 but sequesters PIF3/PAP3 from its target genes promoters in far-red light (PubMed:31732705).[1] [2] [3] [4] [5] [6] [7] Publication Abstract from PubMedPlants employ a divergent cohort of phytochrome (Phy) photoreceptors to govern many aspects of morphogenesis through reversible photointerconversion between inactive Pr and active Pfr conformers. The two most influential are PhyA whose retention of Pfr enables sensation of dim light, while the relative instability of Pfr for PhyB makes it better suited for detecting full sun and temperature. To better understand these contrasts, we solved, by cryo-electron microscopy, the three-dimensional structure of full-length PhyA as Pr. Like PhyB, PhyA dimerizes through head-to-head assembly of its C-terminal histidine kinase-related domains (HKRDs), while the remainder assembles as a head-to-tail light-responsive platform. Whereas the platform and HKRDs associate asymmetrically in PhyB dimers, these lopsided connections are absent in PhyA. Analysis of truncation and site-directed mutants revealed that this decoupling and altered platform assembly have functional consequences for Pfr stability of PhyA and highlights how plant Phy structural diversification has extended light and temperature perception. The structure of Arabidopsis phytochrome A reveals topological and functional diversification among the plant photoreceptor isoforms.,Burgie ES, Li H, Gannam ZTK, McLoughlin KE, Vierstra RD, Li H Nat Plants. 2023 Jul;9(7):1116-1129. doi: 10.1038/s41477-023-01435-8. Epub 2023 , Jun 8. PMID:37291396[8] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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