Institute of General Botany and Plant Physiology, Friedrich-Schiller-University, Am Planetarium 1, 07743, Jena, Germany.
Protoplasma. 2010 Aug;244(1-4):3-14. doi: 10.1007/s00709-010-0113-0. Epub 2010 Feb 20.
The unicellular green alga Chlamydomonas reinhardtii has two flagella and a primitive visual system, the eyespot apparatus, which allows the cell to phototax. About 40 years ago, it was shown that the circadian clock controls its phototactic movement. Since then, several circadian rhythms such as chemotaxis, cell division, UV sensitivity, adherence to glass, or starch metabolism have been characterized. The availability of its entire genome sequence along with homology studies and the analysis of several sub-proteomes render C. reinhardtii as an excellent eukaryotic model organism to study its circadian clock at different levels of organization. Previous studies point to several potential photoreceptors that may be involved in forwarding light information to entrain its clock. However, experimental data are still missing toward this end. In the past years, several components have been functionally characterized that are likely to be part of the oscillatory machinery of C. reinhardtii since alterations in their expression levels or insertional mutagenesis of the genes resulted in defects in phase, period, or amplitude of at least two independent measured rhythms. These include several RHYTHM OF CHLOROPLAST (ROC) proteins, a CONSTANS protein (CrCO) that is involved in parallel in photoperiodic control, as well as the two subunits of the circadian RNA-binding protein CHLAMY1. The latter is also tightly connected to circadian output processes. Several candidates including a significant number of ROCs, CrCO, and CASEIN KINASE1 whose alterations of expression affect the circadian clock have in parallel severe effects on the release of daughter cells, flagellar formation, and/or movement, indicating that these processes are interconnected in C. reinhardtii. The challenging task for the future will be to get insights into the clock network and to find out how the clock-related factors are functionally connected. In this respect, system biology approaches will certainly contribute in the future to improve our understanding of the C. reinhardtii clock machinery.
单细胞绿藻莱茵衣藻有两个鞭毛和一个原始的视觉系统，眼点器官，使细胞能够光趋性。大约 40 年前，人们发现生物钟控制着它的趋光运动。从那时起，已经有几个生物钟节律被描述，如趋化性、细胞分裂、对紫外线的敏感性、与玻璃的附着力或淀粉代谢。随着其整个基因组序列的可用性，以及同源性研究和几个亚蛋白组的分析，莱茵衣藻成为研究其生物钟在不同组织层次的优秀真核模式生物。先前的研究指出了几个可能的光受体，它们可能参与将光信息传递给生物钟。然而，为此目的仍然缺少实验数据。在过去的几年中，已经有几个功能被鉴定的成分，它们很可能是莱茵衣藻振荡机制的一部分，因为它们的表达水平的改变或基因的插入诱变导致至少两个独立测量的节律的相位、周期或幅度的缺陷。这些成分包括几个叶绿体节律（ROC）蛋白、一种参与光周期控制的 CONSTANS 蛋白（CrCO），以及生物钟 RNA 结合蛋白 CHLAMY1 的两个亚基。后者也与生物钟输出过程紧密相连。几个候选者，包括大量的 ROC、CrCO 和表达改变会影响生物钟的酪蛋白激酶 1，它们对生物钟的平行影响也对母细胞的释放、鞭毛形成和/或运动有严重影响，表明这些过程在莱茵衣藻中是相互关联的。未来的挑战将是深入了解时钟网络，并找出时钟相关因素是如何在功能上相互连接的。在这方面，系统生物学方法肯定会在未来有助于提高我们对莱茵衣藻时钟机制的理解。
