Kleine Tatjana, Lockhart Peter, Batschauer Alfred
FB Biologie/Pflanzenphysiologie, Philipps-Universität, Karl-von-Frisch-Str. 8, 35032 Marburg, Germany.
Plant J. 2003 Jul;35(1):93-103. doi: 10.1046/j.1365-313x.2003.01787.x.
Cryptochromes (CRYs) are blue/UV-A photoreceptors related to the DNA repair enzyme DNA photolyase. They have been found in plants, animals and most recently in the cyanobacterium Synechocystis. Closely related to the Synechocystis cryptochrome is the Arabidopsis gene At5g24850. Here, we show that the encoded protein of At5g24850 binds flavin adenine dinucleotide (FAD). It has no photolyase activity, and is likely to function as a photoreceptor. We have named it At-cry3 to distinguish it from the other Arbabidopsis cryptochrome homologues At-cry1 and At-cry2. At-cry3 carries an N-terminal sequence, which mediates import into chloroplasts and mitochondria. Furthermore, we show that At-cry3 binds DNA. DNA binding was also demonstrated for the Synechocystis cryptochrome, indicating that both photoreceptors could have similar modes of action. Based on the finding of a new cryptochrome class in bacteria and plants, it has been suggested that cryptochromes evolved before the divergence of eukaryotes and prokaryotes. However, our phylogenetic analyses are also consistent with an alternative explanation that the presence of cryptochromes in the plant nuclear genome is the result of dual horizontal gene transfer. That is, CRY1 and CRY2 genes may originate from an endosymbiotic ancestor of modern-day alpha-proteobacteria, while the CRY3 gene may originate from an endosymbiotic ancestor of modern-day cyanobacteria.
隐花色素（CRYs）是与DNA修复酶DNA光解酶相关的蓝光/UV-A光感受器。它们已在植物、动物中被发现，最近在蓝藻集胞藻中也有发现。与集胞藻隐花色素密切相关的是拟南芥基因At5g24850。在此，我们表明At5g24850编码的蛋白质结合黄素腺嘌呤二核苷酸（FAD）。它没有光解酶活性，可能作为光感受器发挥作用。我们将其命名为At-cry3，以区别于其他拟南芥隐花色素同源物At-cry1和At-cry2。At-cry3带有一个N端序列，该序列介导其导入叶绿体和线粒体。此外，我们表明At-cry3结合DNA。集胞藻隐花色素也被证明能结合DNA，这表明这两种光感受器可能具有相似的作用模式。基于在细菌和植物中发现的一类新的隐花色素，有人提出隐花色素在真核生物和原核生物分化之前就已进化。然而，我们的系统发育分析也与另一种解释一致，即植物核基因组中隐花色素的存在是双重水平基因转移的结果。也就是说，CRY1和CRY2基因可能起源于现代α-变形菌的内共生祖先，而CRY3基因可能起源于现代蓝藻的内共生祖先。
