Photoreceptor that mediates primarily blue light inhibition of hypocotyl elongation and photoperiodic control of floral initiation, and regulates other light responses, including circadian rhythms, tropic growth, stomata opening, guard cell development, root development, bacterial and viral pathogen responses, abiotic stress responses, cell cycles, programmed cell death, apical dominance, fruit and ovule development, seed dormancy, and magnetoreception. Photoexcited cryptochromes interact with signaling partner proteins to alter gene expression at both transcriptional and post-translational levels and, consequently, regulate the corresponding metabolic and developmental programs (PubMed:21841916). Blue-light absorbing flavoprotein that activates reversible flavin photoreduction via an electron transport chain comprising a tryptophan triad (W-321, W-374 and W-397), or via an alternative electron transport that involves small metabolites, including NADPH, NADH, and ATP. The half-life of the activated signaling state is about 16 minutes (PubMed:25428980, PubMed:23398192). Perceives low blue light (LBL) and responds by directly contacting two bHLH transcription factors, PIF4 and PIF5, at chromatin on E-box variant 5'-CA[CT]GTG-3' to promote their activity and stimulate specific gene expression to adapt global physiology (e.g. hypocotyl elongation and hyponastic growth in low blue light) (PubMed:26724867, PubMed:19558423). In response to blue light, binds to CIB proteins (e.g. BHLH63/CIB1 and BHLH76/CIB5) to activates transcription and floral initiation (PubMed:24130508). Mediates blue light-induced gene expression, floral initiation and hypocotyl elongation through the interaction with SPA1 that prevents formation of SPA1/COP1 complex but stimulates COP1 binding, and thus inhibits COP1-mediated degradation of transcription factors (e.g. CO and HY5) (PubMed:21514160, PubMed:21511872, PubMed:16093319). Promotes flowering time in continuous light (LL) (PubMed:21296763). Involved in shortening the circadian clock period, especially at 27 degrees Celsius, in blue light (BL). Required to maintain clock genes expression rhythm (PubMed:23511208). Triggers nuclear accumulation of ROS in response to blue light illumination (PubMed:26179959). Involved in blue light-dependent stomatal opening, transpiration and inhibition of stem and root growth, probably by regulating abscisic acid (ABA) (PubMed:22147516, PubMed:16093319, PubMed:16703358, PubMed:9482948, PubMed:9565033). Regulates the timing of flowering by promoting the expression of 'FLOWERING LOCUS T' (FT) in vascular bundles. Negatively regulated by 'FLOWERING LOCUS C' (FLC) (PubMed:14605222, PubMed:17259260). General positive regulator of reversible low light-induced chromatin decompaction (PubMed:20935177). Involved in triggering chromatin decondensation during floral transition (PubMed:17470059). Together with phototropins, involved in phototropism regulation by various blue light fluence; blue light attenuates phototropism in high fluence rates (100 umol.m-2.s-1) but enhances phototropism in low fluence rates (<1.0 umol.m-2.s-1) (PubMed:12857830). The effect of near-null magnetic field on flowering is altered by changes of blue light cycle and intensity in a CRY1/CRY2-dependent manner (PubMed:26095447). Involved in the strigolactone signaling that regulates hypocotyl growth in response to blue light (PubMed:24126495). Confers resistance to turnip crinkle virus (TCV) by preventing COP1-mediated proteasome-mediated degradation of RPP8/HRT, thus promoting its stability in light. Exposure to darkness or blue-light induces degradation of CRY2, and in turn of RPP8/HRT, resulting in susceptibility to TCV. Binds 1 FAD per subunit. The flavin in the dark is in the oxidized (bright yellow) redox state, whereas it becomes reduced subsequent to light activation and formation of the neutral radical (pale yellow). Binds 1 5,10-methenyltetrahydrofolate (MTHF) per subunit. Homodimer (PubMed:11089975, PubMed:11509693, PubMed:17438275, PubMed:27846570). Blue-light dependent dimerization (PubMed:27846570). Interacts with COP1 and PHYB in the nucleus (PubMed:11089975, PubMed:11509693, PubMed:17438275, PubMed:20624951). Binds reversibly to CIBs proteins such as BHLH63/CIB1, BHLH78/CIB2, BHLH74/CIB4 and BHLH76/CIB5 after blue light illumination to stimulate their transcription factor activities (PubMed:18988809, PubMed:22139370, PubMed:24130508, PubMed:24780222). Interacts with PIF4 and PIF5 in the nucleus in response to low blue light (LBL) (PubMed:26724867). Binds to SPA1 in response to blue light, this interaction prevents SPA1/COP1 complex formation but stimulates interaction with COP1, and thus avoid COP1-dependent degradation of the transcription factors CO and HY5 by the proteasome and promotes hypocotyl elongation and floral initiation (PubMed:21514160, PubMed:22139370, PubMed:21511872, PubMed:22739826). Binding to ATP mediates conformational changes which facilitate flavin binding (PubMed:17073458). Interacts with BIC1 in both darkness and light (PubMed:27846570, PubMed:11089975, PubMed:11509693, PubMed:17073458, PubMed:17438275, PubMed:18988809, PubMed:20624951, PubMed:21511872, PubMed:21514160, PubMed:22139370, PubMed:22739826, PubMed:24130508, PubMed:24780222, PubMed:26724867). Interacts with NRP (PubMed:28633330). Present in nuclear bodies (NBs) in blue light (e.g. photobodies) (PubMed:21511872, PubMed:23833191, PubMed:22311776). Translocates from the cytosol to the nucleus in response to blue light illumination (PubMed:26179959). Mostly expressed in the shoot meristems and root tips, and, to a lower extent, in the cotyledons, hypocotyls, and roots. Daily oscillation of protein abundance in plants grown in short days (SD) but not in long days (LD) (PubMed:12578985). Expression levels display circadian oscillations under constant conditions, with a low amplitude and a late phase, with maximal expression around the end of the light phase. Repressed by light (PubMed:11743105). In response to blue light and darkness, phosphorylated, ubiquitinated, and subsequently degraded (at protein level) in a SPA proteins-dependent manner (PubMed:20624951, PubMed:25792146, PubMed:22739826, PubMed:22311776). Transcripts levels oscillate weakly and proportionally to temperature, but protein levels are stable (PubMed:23511208). Accumulates in response to low blue light (LBL) and in low light (PubMed:26724867, PubMed:20935177). The NC80 domain (486-565) contains a major active site responsible for the signal transduction processes regulating both hypocotyl inhibition and floral promotion. The C-terminal tail (564-612) is not required for physiological activity of the protein. Phosphorylated by CK1.3 and CK1.4; in response to blue light. Required for degradation (PubMed:12066190, PubMed:17438275, PubMed:17965271, PubMed:9651577, PubMed:25792146, PubMed:23897926). Adopts an open conformation when phosphorylated upon photoexcitation and thus interacts with signaling partner proteins (PubMed:21841916). Not autophosphorylated, even in complex with FAD cofactor (PubMed:17073458). Ubiquitinated; in response to blue light. Plants show increased root elongation in blue light (PubMed:16703358, PubMed:21511872). Reduced attenuating effect of high fluence rates of blue light in the cry1 cry2 double mutant. Slow rate of curvature at low fluence rates of blue light in cry1 cry2 (PubMed:12857830). The double mutant cry1 cry2 exhibits a reduced impact of near-null magnetic field on flowering in lower blue light intensity and short days (PubMed:26095447). Little detectable phenotype on circadian clock in blue light (BL). The double mutant cry1 cry2 is impaired in blue light signaling, resulting in long-period, lower-amplitude oscillations at 12 and 17 degrees Celsius and completely abolishing rhythms at 27 degrees Celsius (PubMed:23511208). Reduced hyponastic growth (differential growth-driven upward leaf movement) in low blue light fluence (PubMed:19558423). The double mutant cry1 cry2 is hyposensitive to the strigolactone analog GR24 (PubMed:24126495). The mutant cry2 exposed to a background of red light show severely impaired stomatal opening responses to blue light. The double mutant cry1 cry2 has reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday, associated with elevated abscisic acid levels (PubMed:22147516). Mutation sel20 suppresses the inhibitory effect of continuous light (LL) on the hypocotyl elongation of elf3-1. The double mutant elf3 sel20 exhibits a late-flowering phenotype (PubMed:21296763). Impaired chromatin decondensation during the floral transition and in low light conditions (PubMed:20935177). Increased sensitivity to turnip crinkle virus (TCV) and associated with reduced HRT levels and stability, and characterized by hypersensitive response (HR) symptoms (PubMed:20624951). The rapid blue light-mediated reversible interaction between CRY2 and BHLH63/CIB1 is used to design an optogenetic control of target proteins or organelles. Phosphorylation of the C-terminal tail and resulting derepression of NC80 domain may both depend on homodimerization. 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