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. 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. 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). In response to blue light, binds to CIB proteins (e.g. BHLH63/CIB1 and BHLH76/CIB5) to activates transcription and floral initiation. 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). Promotes flowering time in continuous light (LL). Involved in shortening the circadian clock period, especially at 27 degrees Celsius, in blue light (BL). Required to maintain clock genes expression rhythm. Triggers nuclear accumulation of ROS in response to blue light illumination. Involved in blue light-dependent stomatal opening, transpiration and inhibition of stem and root growth, probably by regulating abscisic acid (ABA). Regulates the timing of flowering by promoting the expression of 'FLOWERING LOCUS T' (FT) in vascular bundles. Negatively regulated by 'FLOWERING LOCUS C' (FLC). General positive regulator of reversible low light-induced chromatin decompaction. Involved in triggering chromatin decondensation during floral transition. 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). 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. Involved in the strigolactone signaling that regulates hypocotyl growth in response to blue light.; 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.
