Protein function underlying plasticity of the plant circadian clock

生命在地球上进化，地球绕其轴旋转，因此不断经历总共持续24小时的光明与黑暗循环。因此，大多数，也许是所有的生物体都拥有一个“生物钟”，它的周期约为24小时，决定了各种生理过程发生的时间。时钟并不准确，但每天通过灯光等信号重新设置。人类最熟悉的“昼夜节律”是我们的睡眠/觉醒周期，这是时差反应和轮班工作相关问题的原因。其他包括啮齿动物的运动活动（例如仓鼠在夜间而不是白天在活动轮上跑步）和豆类植物的叶片运动。后一种节奏是在近300年前首次描述的！生物钟为生物体提供了一个显着的优势，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、植物和真菌中的时钟，似乎“设计原理”基本相同，但机制却截然不同。有些细菌含有另一种类型的时钟。这意味着在地球上生命的历史中，“时钟”至少单独进化了四次，这表明了它的关键作用。了解生物钟在植物中的功能是很重要的，特别是因为在许多植物中，它与日照长度相互作用以控制开花时间。随着全球变暖和气候变化的出现，期望扩展特定作物生长的纬度。但是日照长度会随着纬度的变化而变化，因此，为了种子而种植的农作物即使在不同的纬度上生长良好，也可能不会有生产力。如果我们了解了生物钟的工作原理，我们应该能够培育或选择可以在不同纬度高产生长的作物品种。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，其中大部分来自于在含有糖的琼脂平板上生长的整个幼苗的实验，其根部暴露于盛行的光/暗循环。这样的条件显然是无关的一个成熟的植物与其根在黑暗中没有糖！我们在一个更现实的情况下进行了实验，使用成熟的植物，它们的根在恒定的黑暗中，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钟工作方式的看法。首先，生物钟是器官特异性的，例如根中的机械与芽中的机械不同。其次，芽能够向根发送信号，每天重置根时钟。这两种性质在我们的工作之前都没有被怀疑过。总的来说，我们的数据表明，植物时钟机制是“塑料”的（即它取决于所研究的器官和植物的基因组成等条件），而不是“硬连线”。这项资助申请的目的是通过定义这种可塑性的原因和作用来扩展我们的工作。这项工作将在模式植物拟南芥中进行，但从长远来看，数据和想法将转移到作物物种中，例如与马铃薯块茎形成和块茎代谢的控制有关。

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, e.g. 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. Overall our data shows that the plant clock machinery is 'plastic' (i.e. it depends on conditions such as the organ being studied and the genetic makeup of the plant) rather than 'hard-wired'. The aim of this grant application is to extend our work by defining the causes and roles of this plasticity. The work will be carried out with the model plant Arabidopsis but in the longer term the data and ideas will be transferred to crop species, for example in relation to the control of tuber formation and tuber metabolism in potatoes.