Shinohara Mari L, Correa Alejandro, Bell-Pedersen Deborah, Dunlap Jay C, Loros Jennifer J
Department of Genetics, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Eukaryot Cell. 2002 Feb;1(1):33-43. doi: 10.1128/EC.1.1.33-43.2002.
The circadian clock of Neurospora crassa regulates the rhythmic expression of a number of genes encoding diverse functions which, as an ensemble, are adaptive to life in a rhythmic environment of alternating levels of light and dark, warmth and coolness, and dryness and humidity. Previous differential screens have identified a number of such genes based solely on their cycling expression, including clock-controlled gene 9 (ccg-9). Sequence analysis now shows the predicted CCG-9 polypeptide to be homologous to a novel form of trehalose synthase; as such it would catalyze the synthesis of the disaccharide trehalose, which plays an important role in protecting many cells from environmental stresses. Consistent with this, heat, glucose starvation, and osmotic stress induce ccg-9 transcript accumulation. Surprisingly, however, a parallel role in development is suggested by the finding that inactivation of ccg-9 results in altered conidiophore morphology and abolishes the normal circadian rhythm of asexual macroconidial development. Examination of a clock component, FRQ, in the ccg-9-null strain revealed normal cycling, phosphorylation, and light induction, indicating that loss of the conidiation rhythm is not due to changes in either the circadian oscillator or light input into the clock but pointing instead to a defect in circadian output. These data imply an interplay between a role of trehalose in stress protection and an apparent requirement for trehalose in clock regulation of conidiation under constant environmental conditions. This requirement can be bypassed by a daily light signal which drives a light-entrained rhythm in conidiation in the ccg-9-null strain; this bypass suggests that the trehalose requirement is related to clock control of development and not to the developmental process itself. Circadian control of trehalose synthase suggests a link between clock control of stress responses and that of development.
粗糙脉孢菌的生物钟调节许多编码不同功能的基因的节律性表达，这些基因作为一个整体，适应于光照与黑暗、温暖与凉爽、干燥与潮湿交替变化的节律性环境中的生活。先前的差异筛选仅基于其循环表达鉴定了许多这样的基因，包括生物钟控制基因9（ccg-9）。序列分析现在表明，预测的CCG-9多肽与一种新型海藻糖合酶同源；因此它将催化二糖海藻糖的合成，海藻糖在保护许多细胞免受环境压力方面发挥着重要作用。与此一致的是，热、葡萄糖饥饿和渗透胁迫会诱导ccg-9转录物积累。然而，令人惊讶的是，ccg-9失活导致分生孢子形态改变并消除无性大分生孢子发育的正常昼夜节律，这一发现表明其在发育中具有平行作用。在ccg-9缺失菌株中对生物钟组件FRQ的检测显示其正常循环、磷酸化和光诱导，这表明分生孢子形成节律的丧失不是由于生物钟振荡器的变化或进入生物钟的光输入的变化，而是指向生物钟输出的缺陷。这些数据意味着海藻糖在应激保护中的作用与在恒定环境条件下分生孢子形成的生物钟调节中对海藻糖的明显需求之间存在相互作用。每日的光信号可以绕过这一需求，该光信号在ccg-9缺失菌株中驱动分生孢子形成的光诱导节律；这种绕过表明对海藻糖的需求与发育的生物钟控制有关，而不是与发育过程本身有关。海藻糖合酶的昼夜节律控制表明应激反应的生物钟控制与发育的生物钟控制之间存在联系。
