Department of Molecular, Cell and Developmental Biology, University of California, Los Angeles, California 90095, USA.
Plant Physiol. 2011 Nov;157(3):1537-45. doi: 10.1104/pp.111.179846. Epub 2011 Sep 7.
Circadian rhythms are autoregulatory, endogenous rhythms with a period of approximately 24 h. A wide variety of physiological and molecular processes are regulated by the circadian clock in organisms ranging from bacteria to humans. Phosphorylation of clock proteins plays a critical role in generating proper circadian rhythms. Casein Kinase2 (CK2) is an evolutionarily conserved serine/threonine protein kinase composed of two catalytic α-subunits and two regulatory β-subunits. Although most of the molecular components responsible for circadian function are not conserved between kingdoms, CK2 is a well-conserved clock component modulating the stability and subcellular localization of essential clock proteins. Here, we examined the effects of a cka1a2a3 triple mutant on the Arabidopsis (Arabidopsis thaliana) circadian clock. Loss-of-function mutations in three nuclear-localized CK2α subunits result in period lengthening of various circadian output rhythms and central clock gene expression, demonstrating that the cka1a2a3 triple mutant affects the pace of the circadian clock. Additionally, the cka1a2a3 triple mutant has reduced levels of CK2 kinase activity and CIRCADIAN CLOCK ASSOCIATED1 phosphorylation in vitro. Finally, we found that the photoperiodic flowering response, which is regulated by circadian rhythms, was reduced in the cka1a2a3 triple mutant and that the plants flowered later under long-day conditions. These data demonstrate that CK2α subunits are important components of the Arabidopsis circadian system and their effects on rhythms are in part due to their phosphorylation of CIRCADIAN CLOCK ASSOCIATED1.
昼夜节律是一种内源性的自我调节节律，其周期约为 24 小时。从细菌到人类等生物体中，广泛的生理和分子过程受到生物钟的调节。时钟蛋白的磷酸化在产生适当的昼夜节律中起着关键作用。酪蛋白激酶 2（CK2）是一种由两个催化α亚基和两个调节β亚基组成的进化上保守的丝氨酸/苏氨酸蛋白激酶。尽管负责昼夜节律功能的大多数分子成分在不同的生物界中并不保守，但 CK2 是一种保守的时钟成分，调节关键时钟蛋白的稳定性和亚细胞定位。在这里，我们研究了 cka1a2a3 三重突变体对拟南芥（Arabidopsis thaliana）生物钟的影响。三个核定位 CK2α亚基的功能丧失突变导致各种生物钟输出节律和中央时钟基因表达的周期延长，表明 cka1a2a3 三重突变体影响生物钟的节奏。此外，cka1a2a3 三重突变体的 CK2 激酶活性和 CIRCADIAN CLOCK ASSOCIATED1 体外磷酸化水平降低。最后，我们发现受昼夜节律调节的光周期开花反应在 cka1a2a3 三重突变体中降低，并且在长日照条件下植物开花较晚。这些数据表明 CK2α亚基是拟南芥生物钟系统的重要组成部分，它们对节律的影响部分归因于它们对 CIRCADIAN CLOCK ASSOCIATED1 的磷酸化。
