A phyB-PIF1-SPA1 kinase regulatory complex promotes photomorphogenesis in Arabidopsis

Nat Commun. 2019 Sep 16;10(1):4216. doi: 10.1038/s41467-019-12110-y.


CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) is a highly conserved E3 ubiquitin ligase from plants to animals and acts as a central repressor of photomorphogenesis in plants. SUPPRESSOR OF PHYA-105 1 family members (SPA1-SPA4) directly interact with COP1 and enhance COP1 activity. Despite the presence of a kinase domain at the N-terminus, no COP1-independent role of SPA proteins has been reported. Here we show that SPA1 acts as a serine/threonine kinase and directly phosphorylates PIF1 in vitro and in vivo. SPAs are necessary for the light-induced phosphorylation, ubiquitination and subsequent degradation of PIF1. Moreover, the red/far-red light photoreceptor phyB interacts with SPA1 through its C-terminus and enhances the recruitment of PIF1 for phosphorylation. These data provide a mechanistic view on how the COP1-SPA complexes serve as an example of a cognate kinase-E3 ligase complex that selectively triggers rapid phosphorylation and removal of its substrates, and how phyB modulates this process to promote photomorphogenesis.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism*
  • Arabidopsis / radiation effects*
  • Arabidopsis Proteins / chemistry
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism*
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Gene Expression Regulation, Plant / radiation effects
  • Light
  • Phytochrome B / chemistry
  • Phytochrome B / genetics
  • Phytochrome B / metabolism*
  • Protein Binding / radiation effects
  • Protein Domains


  • Arabidopsis Proteins
  • Basic Helix-Loop-Helix Transcription Factors
  • Cell Cycle Proteins
  • PHYB protein, Arabidopsis
  • PIF1 protein, Arabidopsis
  • SPA1 protein, Arabidopsis
  • Phytochrome B