CRY1 inhibits COP1-mediated degradation of BIT1, a MYB transcription factor, to activate blue light-dependent gene expression in Arabidopsis

Plant J. 2008 Aug;55(3):361-71. doi: 10.1111/j.1365-313X.2008.03508.x. Epub 2008 Apr 4.


Cryptochromes (CRY) are one of the two major classes of photoreceptors that perceive light stimuli in the UV-A to blue light region and they are involved in multiple aspects of plant growth and development. However, knowledge regarding their signaling transduction components and mechanisms remains limited. Here, we report that a MYB transcription factor Blue Insensitive Trait 1 (BIT1), plays an important role in controlling blue light responses. Hypocotyl growth responses indicate that BIT1 functions as a positive element in blue light signaling, since BIT1 antisense and knock-out lines show a reduced light response in blue light. BIT1 controls blue light-dependent expression of various genes such as PsbS, a member of the light-harvesting complex gene family. A transactivation assay showed that BIT1 regulates promoter activity of PsbS in a blue light-dependent manner and that it requires CRY1 for activation of the PsbS promoter. BIT1 undergoes degradation in darkness and CRY1 functions to stabilize BIT1 in a blue light-dependent manner. In contrast, COP1 binds to BIT1 and mediates its degradation. We propose that the PsbS promoter is activated in blue light via the blue light-dependent stabilization of BIT1 by CRY1, while in darkness BIT1 is degraded by COP1-mediated proteolysis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics*
  • Arabidopsis / metabolism
  • Arabidopsis Proteins / antagonists & inhibitors*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Cryptochromes
  • Flavoproteins / genetics
  • Flavoproteins / metabolism
  • Flavoproteins / physiology*
  • Gene Expression Regulation, Plant*
  • Light*
  • Light-Harvesting Protein Complexes
  • Photosynthetic Reaction Center Complex Proteins / genetics
  • Photosynthetic Reaction Center Complex Proteins / metabolism
  • Photosystem II Protein Complex / genetics
  • Photosystem II Protein Complex / metabolism
  • Promoter Regions, Genetic
  • Signal Transduction / radiation effects
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcription Factors / physiology
  • Ubiquitin-Protein Ligases / antagonists & inhibitors*
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism


  • Arabidopsis Proteins
  • CRY1 protein, Arabidopsis
  • Cryptochromes
  • Flavoproteins
  • Light-Harvesting Protein Complexes
  • NPQ4 protein, Arabidopsis
  • Photosynthetic Reaction Center Complex Proteins
  • Photosystem II Protein Complex
  • Transcription Factors
  • AT2G32950 protein, Arabidopsis
  • Ubiquitin-Protein Ligases