Rhythmic growth explained by coincidence between internal and external cues
Rhythmic growth explained by coincidence between internal and external cues
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DOI：
10.1038/nature05946
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发表时间：
2007-07-19
期刊：
影响因子：
64.8
通讯作者：
Maloof, Julin N.
中科院分区：
文献类型：
--
作者：
Nozue, Kazunari;Covington, Michael F.;Maloof, Julin N.
大多数生物使用昼夜节律振荡器来协调生理和发育过程，如生长与可预测的日常环境变化，如日出和日落。研究表明，昼夜节律障碍会导致细菌(1)和植物(2)的适应性降低，以及人类的睡眠和心理障碍(3)，从而强调了这种协调的重要性。植物细胞生长需要能量和水因子，这些因子因昼夜环境变化而波动。事实上，控制茎生长的两个重要因素是内部昼夜节律振荡器（4-6）和外部光照水平(7)。然而，大多数昼夜节律研究都是在恒定条件下进行的，排除了对生物钟与环境中昼夜变化之间相互作用的机制研究。白天条件下茎伸长的研究揭示了复杂的生长模式，但没有描述机制（8-10）。本研究表明，与连续光照条件下的植物相比，拟南芥幼苗在日间光照条件下的生长阶段发生了8-12小时的变化，并描述了这种环境响应的机制。我们发现时钟调节两个基本螺旋-环-螺旋基因，光敏色素相互作用因子4 （PIF4）和PIF5的转录水平，而光调节它们的蛋白质丰度。这些基因的功能是积极的生长调节剂；高转录水平（在时钟）和蛋白质积累（在黑暗中）的巧合使它们能够在夜晚结束时促进植物生长。因此，这两个基因整合了时钟和光信号，它们的协调调节解释了观察到的昼夜生长节律。这种相互作用可以作为理解内源性和环境信号如何合作控制其他过程的范例。
Most organisms use circadian oscillators to coordinate physiological and developmental processes such as growth with predictable daily environmental changes like sunrise and sunset. The importance of such coordination is highlighted by studies showing that circadian dysfunction causes reduced fitness in bacteria(1) and plants(2), as well as sleep and psychological disorders in humans(3). Plant cell growth requires energy and water-factors that oscillate owing to diurnal environmental changes. Indeed, two important factors controlling stem growth are the internal circadian oscillator(4-6) and external light levels(7). However, most circadian studies have been performed in constant conditions, precluding mechanistic study of interactions between the clock and diurnal variation in the environment. Studies of stem elongation in diurnal conditions have revealed complex growth patterns, but no mechanism has been described(8-10). Here we show that the growth phase of Arabidopsis seedlings in diurnal light conditions is shifted 8-12 h relative to plants in continuous light, and we describe a mechanism underlying this environmental response. We find that the clock regulates transcript levels of two basic helix-loop-helix genes, phytochrome-interacting factor 4 (PIF4) and PIF5, whereas light regulates their protein abundance. These genes function as positive growth regulators; the coincidence of high transcript levels (by the clock) and protein accumulation (in the dark) allows them to promote plant growth at the end of the night. Thus, these two genes integrate clock and light signalling, and their coordinated regulation explains the observed diurnal growth rhythms. This interaction may serve as a paradigm for understanding how endogenous and environmental signals cooperate to control other processes.