Arabidopsis COP1/SPA1 complex and FHY1/FHY3 associate with distinct phosphorylated forms of phytochrome A in balancing light signaling

Mol Cell. 2008 Aug 22;31(4):607-13. doi: 10.1016/j.molcel.2008.08.003.


Fine tuning of light signaling is crucial to plant development. Following light-triggered nuclear translocation, the photoreceptor phytochrome A (phyA) regulates gene expression under continuous far-red light and is rapidly destabilized upon red light irradiation by E3 ubiquitin ligases, including COP1. Here we provide evidence that the light signaling repressors SPA proteins contribute to COP1-mediated phyA degradation and that a COP1/SPA1 protein complex is tightly associated with phyA ubiquitination activity. Furthermore, a phosphorylated phyA form accumulates in the nucleus and preferentially associates with the COP1/SPA1 complex. In contrast, underphosphorylated phyA predominantly associates with the phyA-signaling intermediates FHY3 and FHY1. However, COP1 associates with underphosphorylated phyA in the absence of FHY3 or FHY1, suggesting that phyA associations with FHY3 and FHY1 protect underphosphorylated phyA from being recognized by the COP1/SPA complex. We propose that light-induced phyA phosphorylation acts as a switch controlling differential interactions of the photoreceptor with signal propagation or attenuation machineries.

Publication types

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

MeSH terms

  • Arabidopsis / enzymology
  • Arabidopsis / metabolism*
  • Arabidopsis / radiation effects
  • Arabidopsis Proteins / metabolism*
  • Cell Cycle Proteins / metabolism*
  • Light*
  • Phosphorylation / radiation effects
  • Phytochrome / metabolism*
  • Phytochrome A / metabolism*
  • Protein Binding / radiation effects
  • Signal Transduction / radiation effects
  • Ubiquitin-Protein Ligases / metabolism
  • Ubiquitination / radiation effects


  • Arabidopsis Proteins
  • Cell Cycle Proteins
  • FHY1 protein, Arabidopsis
  • FHY3 protein, Arabidopsis
  • Phytochrome A
  • SPA1 protein, Arabidopsis
  • Phytochrome
  • AT2G32950 protein, Arabidopsis
  • Ubiquitin-Protein Ligases