摘要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 re-main unclear. Here we identify 19 in vivo phos-phorylation 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 phosphory-lated CRY1 to constitutively inhibit hypocotyl elongation. We further demonstrate that phospho-mimetic CRY1 variants exhibit enhanced inter-action with the E3 ubiquitin ligase COP1 (CON-STITUTIVELY 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 PRO-TEIN KINASEs (PPKs) phosphorylate CRY1 in a blue light-dependent manner and that this phos-phorylation is critical for CRY1 signaling and regu-lation. These results indicate that, similar to CRY2, blue light-dependent phosphorylation of CRY1 de-termines its photosensitivity.