Yu Xuhong, Liu Hongtao, Klejnot John, Lin Chentao
Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, CA 90095, USA.
Arabidopsis Book. 2010 Sep 23;8:e0135. doi: 10.1199/tab.0135.
Cryptochromes are photolyase-like blue light receptors originally discovered in Arabidopsis but later found in other plants, microbes, and animals. Arabidopsis has two cryptochromes, CRY1 and CRY2, which mediate primarily blue light inhibition of hypocotyl elongation and photoperiodic control of floral initiation, respectively. In addition, cryptochromes also regulate over a dozen 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. Cryptochromes have two domains, the N-terminal PHR (Photolyase-Homologous Region) domain that bind the chromophore FAD (flavin adenine dinucleotide), and the CCE (CRY C-terminal Extension) domain that appears intrinsically unstructured but critical to the function and regulation of cryptochromes. Most cryptochromes accumulate in the nucleus, and they undergo blue light-dependent phosphorylation or ubiquitination. It is hypothesized that photons excite electrons of the flavin molecule, resulting in redox reaction or circular electron shuttle and conformational changes of the photoreceptors. The photoexcited cryptochrome are phosphorylated to adopt an open conformation, which interacts with signaling partner proteins to alter gene expression at both transcriptional and posttranslational levels and consequently the metabolic and developmental programs of plants.
隐花色素是一类类似于光解酶的蓝光受体，最初在拟南芥中发现，后来在其他植物、微生物和动物中也有发现。拟南芥有两种隐花色素，CRY1和CRY2，它们分别主要介导蓝光对下胚轴伸长的抑制以及光周期对花起始的控制。此外，隐花色素还调控十几种其他光反应，包括昼夜节律、向性生长、气孔开放、保卫细胞发育、根发育、细菌和病毒病原体反应、非生物胁迫反应、细胞周期、程序性细胞死亡、顶端优势、果实和胚珠发育、种子休眠以及磁感受。隐花色素有两个结构域，即结合发色团FAD（黄素腺嘌呤二核苷酸）的N端PHR（光解酶同源区域）结构域，以及本质上无结构但对隐花色素的功能和调控至关重要的CCE（CRY C端延伸）结构域。大多数隐花色素在细胞核中积累，并且它们会经历蓝光依赖的磷酸化或泛素化。据推测，光子激发黄素分子的电子，导致氧化还原反应或循环电子穿梭以及光感受器的构象变化。光激发的隐花色素被磷酸化以采用开放构象，该构象与信号伴侣蛋白相互作用，在转录和翻译后水平改变基因表达，从而影响植物的代谢和发育程序。
