Institute of Molecular and Plant Cellular Biology, Consejo Superior de Investigaciones Científicas-Universidad Politécnica de Valencia, 46022 Valencia, Spain.
Proc Natl Acad Sci U S A. 2011 May 31;108(22):9292-7. doi: 10.1073/pnas.1101050108. Epub 2011 May 16.
Circadian clocks are endogenous timekeeping mechanisms that allow organisms to anticipate rhythmic, daily environmental changes. Temporal coordination of transcription results in a set of gene expression patterns with peak levels occurring at precise times of the day. An intriguing question is how a single clock can generate different oscillatory rhythms, and it has been proposed that hormone signaling might act in plants as a relay mechanism to modulate the amplitude and the phase of output rhythms. Here we show that the circadian clock gates gibberellin (GA) signaling through transcriptional regulation of the GA receptors, resulting in higher stability of DELLA proteins during daytime and higher GA sensitivity at night. Oscillation of GA signaling appears to be particularly critical for rhythmic growth, given that constitutive expression of the GA receptor expands the daily growth period in seedlings, and complete loss of DELLA function causes continuous, arrhythmic hypocotyl growth. Moreover, transcriptomic analysis of a pentuple della KO mutant indicates that the GA pathway mediates the rhythmic expression of many clock-regulated genes related to biotic and abiotic stress responses and cell wall modification. Thus, gating of GA sensitivity by the circadian clock represents an additional layer of regulation that might provide extra robustness to the diurnal growth rhythm and constitute a regulatory module that coordinates the circadian clock with additional endogenous and environmental signals.
生物钟是内源性的计时机制，使生物能够预测有节奏的、日常的环境变化。转录的时间协调导致一组基因表达模式，其峰值水平出现在一天中的精确时间。一个有趣的问题是，单个时钟如何产生不同的振荡节律，有人提出激素信号可能在植物中作为一种中继机制，调节输出节律的幅度和相位。在这里，我们表明生物钟通过对 GA 受体的转录调控来控制赤霉素（GA）信号，从而导致白天 DELLA 蛋白的稳定性更高，夜间 GA 敏感性更高。GA 信号的振荡似乎对节律性生长尤为关键，因为 GA 受体的组成性表达会扩大幼苗的每日生长周期，而 DELLA 功能的完全丧失会导致连续的、无节奏的下胚轴生长。此外，对五倍体 della KO 突变体的转录组分析表明，GA 途径介导与生物和非生物胁迫反应以及细胞壁修饰相关的许多时钟调控基因的节律表达。因此，生物钟对 GA 敏感性的调控代表了一个额外的调节层，可能为昼夜生长节律提供额外的稳健性，并构成一个调节模块，将生物钟与其他内源性和环境信号协调起来。
