4.7 Article

Blue light-induced phosphorylation of Arabidopsis cryptochrome 1 is essential for its photosensitivity

Journal

JOURNAL OF INTEGRATIVE PLANT BIOLOGY
Volume 64, Issue 9, Pages 1724-1738

Publisher

WILEY
DOI: 10.1111/jipb.13331

Keywords

Arabidopsis; blue light; cryptochrome; phosphorylation; PPK

Funding

  1. National Natural Science Foundation of China [31970265, 31801018]
  2. Natural Science Foundation of Guangdong Province [2022A1515011002]
  3. National Key Research and Development Program of China [2020YFA0509700]

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Plants have two cryptochrome photoreceptors, CRY1 and CRY2, which mediate overlapping and distinct physiological responses. This study identified 19 phosphorylation sites in CRY1 and analyzed the physiological and photobiochemical activities of CRY1 variants with phosphosite substitutions. The results showed that phosphorylation of CRY1 is necessary for its degradation, physiological functions, and interaction with the E3 ubiquitin ligase COP1. Additionally, the phosphorylation of CRY1 by photoregulatory protein kinases (PPKs) is critical for CRY1 signaling and regulation.
Plants possess two cryptochrome photoreceptors, cryptochrome 1 (CRY1) and cryptochrome 2 (CRY2), that mediate overlapping and distinct physiological responses. Both CRY1 and CRY2 undergo blue light-induced phosphorylation, but the molecular details of CRY1 phosphorylation remain unclear. Here we identify 19 in vivo phosphorylation sites in CRY1 using mass spectrometry and systematically analyze the physiological and photobiochemical activities of CRY1 variants with phosphosite substitutions. We demonstrate that nonphosphorylatable CRY1 variants have impaired phosphorylation, degradation, and physiological functions, whereas phosphomimetic variants mimic the physiological functions of phosphorylated CRY1 to constitutively inhibit hypocotyl elongation. We further demonstrate that phosphomimetic CRY1 variants exhibit enhanced interaction with the E3 ubiquitin ligase COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1). This finding is consistent with the hypothesis that phosphorylation of CRY1 is required for COP1-dependent signaling and regulation of CRY1. We also determine that PHOTOREGULATORY PROTEIN KINASEs (PPKs) phosphorylate CRY1 in a blue light-dependent manner and that this phosphorylation is critical for CRY1 signaling and regulation. These results indicate that, similar to CRY2, blue light-dependent phosphorylation of CRY1 determines its photosensitivity.

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