Defining the role of PIF3-like bHLH transcription factors in the integration of light and cold signalling in Arabidopsis

植物已经进化出了一种惊人的能力，可以根据环境的信号改变它们的生长和发育方式。这对它们的生存至关重要，因为这使它们能够与季节变化同步生长和发育。一个很好的例子是种子发芽的过程，它标志着经过一段时间的静止或休眠后生长的开始。休眠状态使种子能够在土壤中存活数月至数年，直到条件有利于生长。感知环境条件的能力对种子来说是至关重要的，因为一旦它开始生长，脆弱的幼苗就非常容易受到各种环境挑战的影响。温度和光是影响种子休眠中断的两个关键环境信号。在模式植物拟南芥（Arabidopsis thaliana）中，低温和光照的结合消除了休眠。这种对冬季低温的要求确保了种子只有在春天条件适宜生长时才发芽。光照要求意味着种子只有在土壤表面或接近土壤表面时才会发芽。我们对植物如何整合冷和光信号知之甚少。我们最近发现一种叫做SPT的蛋白质会抑制种子的萌发，直到种子暴露在寒冷中。我们还发现，另一种名为PIL5的相关蛋白抑制种子发芽，直到种子暴露在光线下。SPT和PIL5都属于一类被称为转录因子的蛋白质，因为它们调节特定基因的表达。SPT和PIL5抑制参与植物激素赤霉素（GA）合成的关键基因的表达。我们从以前的研究中知道，赤霉素促进发芽。GA还通过降低DELLA蛋白的活性来促进其他一系列反应。我们最近的数据显示，去除这些DELLA蛋白会增加发芽率。我们现在第一次有证据表明，光和冷信号与种子发芽的变化有关。这幅图景开始浮现，即转录因子蛋白SPT和PIL5调节植物激素GA的水平。这种GA反过来调节控制发芽的DELLA蛋白。然而，这肯定不是全部，因为我们有其他证据表明SPT和PIL5蛋白也对发芽产生不依赖于GA的影响。有趣的是，这种响应环境信号的发芽控制机制似乎也控制着其他生理过程，如幼苗叶片大小。我们现在需要制定出这一重要机制的细节。我们的最终目标是充分了解这一过程的不同部分，这样我们就可以建立一个模型，使我们能够预测环境条件变化对植物生长的影响，特别是在种子萌发和幼苗建立的发育窗口。植物对不同环境条件的反应可以影响影响作物产量的重要农艺性状。通过这项工作获得的知识可能会改善重要作物的这些性状。

Plants have evolved an amazing ability to alter how they grow and develop in response to signals from their environment. This is critical for their survival as it allows them to synchronise growth and development with seasonal changes. A good example of this is the process of seed germination, which marks the start of growth following a period of quiescence or dormancy. The dormancy state enables seeds to survive in the soil for months to years until the conditions are favourable for growth. The ability to sense environmental conditions is critical for a seed, because once it starts to grow the fragile seedling is extremely vulnerable to all sorts of environmental challenges. Temperature and light are two key environmental signals that influence seed dormancy breakage. In the model plant, Arabidopsis thaliana, dormancy is removed by a combination of cold temperatures and light. This requirement for cold temperatures as experienced in winter ensures that seeds only germinate in spring when conditions are good for growth. The light requirement means that seeds will only germinate when they are at or near the soil surface. Very little is known about how plants integrate cold and light signals. We recently discovered that a protein called SPT represses germination until seeds are exposed to cold. We have also found that a second related protein called PIL5 represses seed germination until seeds are exposed to light. Both SPT and PIL5 belong to a class of proteins called transcription factors, because they regulate expression of specific genes. SPT and PIL5 repress expression of key genes involved in the synthesis of a plant hormone called gibberellic acid (GA). We know from previous studies that GA promotes germination. GA also promotes a host of other responses where it acts by decreasing the activity of DELLA proteins. Our most recent data reveal that removal of these DELLA proteins increases germination frequency. For the first time we now have evidence that links light and cold signals with changes in germination of the seed. The picture that is beginning to emerge is that the transcription factor proteins SPT and PIL5 regulate levels of the plant hormone GA. This GA in turn regulates the DELLA proteins that control germination. However, this is most certainly not the whole story as we have other evidence that suggests the SPT and PIL5 proteins also exert GA independent effects on germination. Intriguingly, this mechanism of germination control in response to signals from the environment also appears to control other physiological processes such as seedling leaf size. We now need to work out the details of this important mechanism. Our ultimate aim is to fully understand the different parts of this process so that we can build a model that allows us to predict the effect of changing environmental conditions on plant growth particularly in the developmental window of seed germination and seedling establishment . How plants respond to different environmental conditions can affect important agronomic traits which impact on crop yield. Knowledge gained through this work could lead to improvement of these traits in important crop plants.