Organ communication in the Arabidopsis circadian clock

生命是在地球上进化出来的，地球绕着它的轴旋转，因此不断地经历一个总共持续24小时的光明和黑暗的循环。因此，大多数，也许是所有的生物体都有一个“生物钟”，其周期约为24小时，它决定了各种生理过程发生的时间。这种时钟并不精确计时，而是每天通过光线等信号重新调整。人类最熟悉的“昼夜节律”是我们的睡眠/觉醒周期，这是时差和倒班相关问题的原因。其他包括啮齿类动物的运动活动（例如，仓鼠在夜间而不是白天在活动轮上奔跑）和豆类植物的叶片运动。后一种节奏最早是在近300年前被描述的！生物钟为生物体提供了一个显著的优势，因为它允许它们预测光/暗的变化，并相应地调整它们的行为，而不仅仅是对变化做出反应。比较动物、植物和真菌的生物钟，似乎它们的“设计原则”基本相同，但其机制却大不相同。一些细菌含有另一种类型的时钟。这意味着，在地球生命史上，“时钟”至少单独进化了四次，表明了它的关键作用。了解生物钟在植物中的作用方式是很重要的，特别是因为在许多植物中，它与白昼长度相互作用来控制开花时间。随着全球变暖和气候变化的到来，人们希望扩大特定作物生长的纬度。但是白天的长度随着纬度的变化而变化，所以为了种子而种植的作物在不同的纬度可能并不高产，即使它们长得很好。如果我们了解生物钟是如何工作的，我们应该能够培育或选择能够在不同纬度高效生长的作物变种。在过去的十年里，我们对植物生物钟机制的理解有了巨大的进步。然而，这些实验大多来自于在含有糖的琼脂板上生长的整株幼苗的实验，它们的根暴露在普遍的光/暗循环中。这样的条件显然与成熟的植物无关，因为它的根在黑暗中没有糖！我们在更现实的情况下进行了实验，使用成熟的植物，它们的根处于持续的黑暗中，而它们的叶子暴露在光/暗循环中。我们有两个发现从根本上影响了我们对植物生物钟工作方式的看法。首先，生物钟是器官特异性的，即根部的机制与茎部的机制不同。其次，茎能够向根发送一个信号，每天重新设置根时钟。在我们的工作之前，这些性质都没有被怀疑过。这项拨款申请的目的是扩展我们的工作，并定义成熟植物不同器官中生物钟的机制和功能。

Life has evolved on the planet Earth, which rotates on its axis, and therefore continuously undergoes a cycle of light and darkness lasting 24 h in total. As a result, most, perhaps all, organisms possess a 'circadian clock' that has a period of about 24 h and that determines the time at which various physiological processes occur. The clock does not keep exact time but is re-set each day by signals such as light. The 'circadian rhythm' most familiar to humans is our sleep/wake cycle, the cause of jetlag and problems associated with shiftwork. Others include locomotor activity in rodents (e.g. hamsters run on an activity wheel at night rather than in the day) and leaf movements in bean plants. The latter rhythm was first described nearly 300 years ago! The circadian clock provides organisms with a significant advantage because it allows them to anticipate light/dark changes and adjust their behaviour accordingly, not just react to the changes. Comparing the clock in animals, plants and fungi, it seems that the 'design principles' are basically the same but the machinery is quite different. Some bacteria contain another type of clock. This implies that a 'clock' has evolved separately at least four times during the history of life on earth, indicating the key nature of its role. It is important to understand the way that the circadian clock functions in plants, particularly because in many plants it interacts with daylength to control flowering time. With the advent of global warming and climate change, it is desirable to extend the latitude at which particular crops grow. But daylength changes with latitude, so crop plants grown for their seeds may not be productive at different latitudes even if they can grow well. If we understand how the clock works, we should be able to breed or select crop variants that can grow productively at different latitudes. There have been huge advances in the last ten years or so in our understanding of the mechanism of the circadian clock in plants. However most of these have come from experiments on whole seedlings grown on agar plates containing sugars, with their roots exposed to the prevailing light/dark cycle. Such conditions are clearly irrelevant to a mature plant with its roots in the dark without sugars! We have carried out experiments in a more realistic situation, using mature plants with their roots in constant darkness while their leaves are exposed to the light/dark cycle. We have made two findings that radically affect the way we think the plant clock works. First, the clock is organ-specific, i.e. the machinery in the root is not the same as in the shoot. Secondly, the shoot is able to send a signal to the root that re-sets the root clock each day. Neither of these properties had been suspected before our work. The aim of this grant application is to extend our work and define the machinery and the functions of the circadian clock in different organs of mature plants.