The Circadian Clock Regulates the Photoperiodic Response of Hypocotyl Elongation through a Coincidence Mechanism in Arabidopsis thaliana
The Circadian Clock Regulates the Photoperiodic Response of Hypocotyl Elongation through a Coincidence Mechanism in Arabidopsis thaliana
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DOI：
10.1093/pcp/pcp028
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发表时间：
2009-04-01
影响因子：
4.9
通讯作者：
Mizuno, Takeshi
中科院分区：
文献类型：
--
作者：
Niwa, Yusuke;Yamashino, Takafumi;Mizuno, Takeshi
植物生物钟产生周期接近24小时的节律，它控制着自然光暗循环下栖息地的广泛的生理和发育振荡。在时钟控制的发育事件中，最具特征的是拟南芥开花时间的光周期控制。最近，还有报道称，生物钟调节下胚轴的日常和有节奏的伸长。在这里，我们报告说，下胚轴伸长的促进实际上取决于光周期的变化，尤其是在短日照条件下，下胚轴伸长会加速。在这方面，我们提供了遗传证据来表明生物钟通过调节编码光敏色素相互作用bHLH（碱性螺旋螺旋）因子的PIF4和PIF5基因的表达谱来调节下胚轴的光周期（或季节性）伸长，从而需要某些短日照条件来增强这些基因在夜间的表达。换句话说，长日照条件不足以打开夜间触发PIF4和PIF5表达的时钟门。基于这些和其他结果，由于内部（昼夜节律）和外部（光周期）时间线索之间的重合，下胚轴伸长的光周期控制最好由 PIF4 和 PIF5 在短日夜间的积累来解释。这种机制是光周期依赖性促进开花的镜像，因为植物应该经历长日照条件才能迅速开始开花。这两种时钟介导的重合机制可以协调地赋予在不同光周期的自然栖息地中生长的植物的生态适应性。
The plant circadian clock generates rhythms with a period close to 24h, and it controls a wide range of physiological and developmental oscillations in habitats under natural lightdark cycles. Among clock-controlled developmental events, the best characterized is the photoperiodic control of flowering time in Arabidopsis thaliana. Recently, it was also reported that the clock regulates a daily and rhythmic elongation of hypocotyls. Here, we report that the promotion of hypocotyl elongation is in fact dependent on changes in photoperiods in such a way that an accelerated hypocotyl elongation occurs especially under short-day conditions. In this regard, we provide genetic evidence to show that the circadian clock regulates the photoperiodic (or seasonal) elongation of hypocotyls by modulating the expression profiles of the PIF4 and PIF5 genes encoding phytochrome-interacting bHLH (basic helixloophelix) factors, in such a manner that certain short-day conditions are necessary to enhance the expression of these genes during the night-time. In other words, long-day conditions are insufficient to open the clock-gate for triggering the expression of PIF4 and PIF5 during the night-time. Based on these and other results, the photoperiodic control of hypocotyl elongation is best explained by the accumulation of PIF4 and PIF5 during the night-time of short days, due to coincidence between the internal (circadian rhythm) and external (photoperiod) time cues. This mechanism is a mirror image of the photoperiod-dependent promotion of flowering in that plants should experience long-day conditions to initiate flowering promptly. Both of these clock-mediated coincidence mechanisms may coordinately confer ecological fitness to plants growing in natural habitats with varied photoperiods.