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Nat Commun. 2017 May 11;8:15236. doi: 10.1038/ncomms15236.

PPKs mediate direct signal transfer from phytochrome photoreceptors to transcription factor PIF3.

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Department of Plant and Microbial Biology, University of California, Berkeley, California 94720, USA.
U.S. Department of Agriculture/Agriculture Research Service, Plant Gene Expression Center, Albany, California 94710, USA.
Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143, USA.
Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305, USA.
Thermo Fisher Scientific, San Jose, California 95134, USA.


Upon light-induced nuclear translocation, phytochrome (phy) sensory photoreceptors interact with, and induce rapid phosphorylation and consequent ubiquitin-mediated degradation of, transcription factors, called PIFs, thereby regulating target gene expression and plant development. Nevertheless, the biochemical mechanism of phy-induced PIF phosphorylation has remained ill-defined. Here we identify a family of nuclear protein kinases, designated Photoregulatory Protein Kinases (PPK1-4; formerly called MUT9-Like Kinases (MLKs)), that interact with PIF3 and phyB in a light-induced manner in vivo. Genetic analyses demonstrate that the PPKs are collectively necessary for the normal light-induced phosphorylation and degradation of PIF3. PPK1 directly phosphorylates PIF3 in vitro, with a phosphosite pattern that strongly mimics the light-induced pattern in vivo. These data establish that the PPKs are directly involved in catalysing the photoactivated-phy-induced phosphorylation of PIF3 in vivo, and thereby are critical components of a transcriptionally centred signalling hub that pleiotropically regulates plant growth and development in response to multiple signalling pathways.

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