The Arabidopsis Cryptochrome 1 Structure And Function Of The Relationship Between Biochemical Mechanism

For plants, sunlight is one of the most important environmental stimuli,acting as both energy source of photosynthesis and developmental signal. Thefamily of plants cryptochromes (CRYs) are blue light photoreceptors, whosesignaling pathway is critical for the regulation of the developmental growth.The N-terminal domain of CRYs (CNT) shares sequence similarity to photolyases,flavoproteins that catalyze the repair of UV light-damaged DNA, and itsC-terminus extension (CCT) is unique. In earlier studies, the Arabidopsisthaliana seedlings overexpressing CCT fused to C-terminus of β-glucuronidase(GUS) displayed a consititutively photomorphogenic (COP) phenotype, indicatingthat the functions of CRYs are mediated by CCT and that CNT acts as repressorof CCT through intramolecular interactions in a blue light-dependent manner.However, we found that overexpression of CNT1 in wild type Arabidopsis resultsin dominant negative phenotype, suggesting that the functional regulation ofCCT1 by CNT1 is mediated by intermolecular interactions. Based on theproposition and using an array of biochemical studies, we demonstrated here thatthe constitutive homodimerization of CRY1 is mediated by CNT1 and mutations ofCNT1 that result in reduced blue light response can block the formation of thedimmer. We also demonstrated that GUS exists as multimer in vivo, which isessential for COP phenotype resulted from overexpression of GUS-CCT fusionproteins. These results indicate that irradiation with blue light modifies theproperties of CNT1 dimer, resulting in a change in CCT1, activating CCT1, andeventually triggering the CRY1 signaling pathway.