The role of the oxylipin OPDA in the seasonal sensitivity of seed dormancy

季节性植物生长通常在春季萌芽或种子萌发时开始，随着秋季到冬季休眠的开始而终止，这是一种公认的自然现象，可以影响全球范围内的年度大气气体交换。众所周知，日长和温度等环境信号会直接影响植物的生长和发育，但对于植物如何利用这些信号在重大季节变化之前建立休眠状态，我们知道的要少得多。人们越来越有兴趣了解导致这些预测性反应的潜在机制，尤其是因为这些知识将帮助我们预测野生植物和作物将如何对环境变化做出反应。我们最近有了两项重要发现，表明一种名为OPDA的脂质信号分子在控制种子休眠方面发挥着核心作用，并参与了控制季节性生长控制的信息从一代传到下一代。这两项发现都是在模式植物拟南芥中发现的，但所获得的知识将适用于其他植物物种。在第一个发现中，我们发现OPDA的升高是导致几个拟南芥突变体种子休眠增加的原因。外源OPDA处理抑制种子萌发，我们有证据表明它至少涉及一个下游靶标，称为ABI5的转录因子蛋白，在OPDA存在时增加丰度，是OPDA在β-氧化突变体种子中实施休眠所必需的。在第二个发现中，我们发现拟南芥植物生长的日长对营养组织中的OPDA水平和下一代种子的休眠状态有很大的影响。这种对OPDA和种子休眠的影响依赖于一种名为Flowering Locus T(FT)的蛋白质，该蛋白质参与调节参与OPDA合成的关键基因在营养组织中的表达。现在需要解决的一个主要问题是，营养组织中对日长的“记忆”如何传递给下一代，并在种子的休眠状态中表现出来。我们的初步研究表明，OPDA在从营养物质到种子的世代记忆保持中发挥着核心作用。此外，最近的其他工作表明，在多年生植物中，如杨树，FT蛋白控制营养芽休眠的类似机制。本研究的目的是通过改变营养芽和种子的休眠状态来建立环境信号影响季节生长的机制。为了实现这一目标，我们将首先确定FT蛋白如何调节营养组织中的OPDA水平，并建立依赖FT的信息从一代传递到下一代的机制。最可能的机制是一种涉及表观遗传的DNA非永久性修饰，这种修饰可以影响基因表达，从而影响一代又一代的特征和表型。在这项工作的同时，我们将确定种子发育期间的环境信号如何影响休眠状态和OPDA水平。我们还将阐明OPDA介导的种子休眠控制的信号转导途径。最后，在我们显著观察到种子结实期间经历的环境影响从该种子衍生的植物的生长速度的基础上，我们将调查是否涉及种子成熟环境的表观遗传OPDA依赖的记忆。这项研究的结果将影响我们预测植物生态系统如何应对环境变化的方式。它还可能影响改进的农艺做法的发展，以生产休眠程度较低的种子和/或生长更旺盛的作物。

Seasonal plant growth, typically initiated with the onset of bud burst or seed germination in the spring and terminated with the onset of dormancy in the progression through autumn to winter, is a well recognised natural phenomenon that can affect annual atmospheric gas exchange on a global scale. Environmental cues such as day-length and temperature are well known to directly affect plant growth and development, but much less is known about how such cues are used by plants to establish dormancy in advance of major seasonal change. There is a growing interest in understanding the underlying mechanism responsible for these predictive responses, not least because such knowledge will help us to predict how wild plants and crops will respond to environmental change. We have recently made two important discoveries that point to a lipid signalling molecule, OPDA, having a central role in controlling dormancy in seeds and being involved in the transfer of information governing seasonal growth control from one generation to the next. Both of these discoveries were made in the model plant species Arabidopsis thaliana, but knowledge gained will be applicable to other plant species. In the first discovery we found that elevated OPDA is responsible for increased seed dormancy in several Arabidopsis mutants. Exogenous OPDA application inhibits germination and we have evidence to show it involves at least one downstream target, a transcription factor protein called ABI5 that increases in abundance in the presence of OPDA and is essential for the OPDA imposed dormancy in beta-oxidation mutant seeds. In the second discovery we found that the day-length in which Arabidopsis plants are grown has a dramatic effect on the levels of OPDA in vegetative tissues and the dormancy state of seeds in the next generation. This effect on OPDA and seed dormancy is dependent on a protein called Flowering Locus T (FT) that is involved in regulating expression in vegetative tissues of a key gene involved in the synthesis of OPDA. A major question that now needs to be addressed is how the 'memory' of day-length in vegetative tissues is transmitted to the next generation and manifested in the dormancy status of seeds. Our preliminary studies indicate that OPDA plays a central role in the memory retention across generations from vegetative material to seeds. Furthermore, other recent work suggests a similar mechanism involving the FT protein controls dormancy in vegetative buds in perennial species such as poplar trees. The aim of our research is to establish the mechanism by which environmental signals influence seasonal growth by modification of the dormancy state of vegetative buds and seeds. To achieve this aim we will first establish how the FT protein regulates OPDA levels in vegetative tissues and establish the mechanism by which FT-dependent information is transferred from one generation to the next. The most likely mechanism is one involving epigenetic non-permanent modification of DNA that can affect gene expression and hence traits and phenotypes from one generation to the next. In parallel with this work we will establish how environmental signals during seed development influence dormancy state and OPDA levels. We will also elucidate the signal transduction pathway involved in the OPDA mediated control of seed dormancy. Finally, building on our remarkable observation that the environment experienced during seed set influences the growth rate of plants derived from that seed, we will investigate if an epigenetic OPDA-dependent memory of the seed maturation environment is involved. The outputs of this research will impact on the way we predict how plant ecosystems respond to environmental change. It may also impact on the development of improved agronomic practice for the production of seeds that are less dormant and/or give rise to crops that grow more vigorously.