The novel gene 'Histone Deacetylase Complex 1' enhances plant growth and abiotic stress tolerance; where, when and with whom?

气候变化和不断增长的世界人口预计将在不久的将来导致水资源短缺和粮食短缺。迫切需要提高粮食作物的产量、水分利用效率和抗逆性。我们建议通过控制植物对‘胁迫’激素脱落酸(ABA)的敏感性来实现这一点。该项目建立在我们最近从拟南芥中发现的一个新基因的基础上，我们称之为‘组蛋白去乙酰化复合体1’(HDC1)。我们发现，HDC1的过度表达降低了萌发种子对ABA的敏感性，促进了成熟植株的生长，而HDC1的缺失则具有相反的效果。因此，HDC1可以用作可调节的“恒功器”。这一特性使HDC1成为作物改良的一个有吸引力的目标。例如，在干旱易受雨水灌溉的田地，增加对ABA的敏感性将有助于植物脱水后的恢复，而在灌溉田地，降低对ABA的敏感性可能是一种在减少水分投入的情况下维持生物量生产的手段。那么，问题是：HDC1如何改变对ABA的敏感性？酵母中HDC1的祖先前体是大型多蛋白复合体的成员，这些复合体对与DNA(染色质)相关的组蛋白进行生物化学修饰(去乙酰化)。组蛋白去乙酰化(HD)决定了DNA的整体结构，而DNA的整体结构反过来又对基因活性施加了高度的控制。我们目前的假设是，HDC1‘滴定’染色质复合体的稳定性，从而改变DNA对ABA依赖的调节剂的可及性，从而改变ABA的敏感性。这是一个令人兴奋的概念，因为它意味着通过HDC1，人们可以获得对一整套压力反应的控制，而不需要修修补补底层复杂的信号网络。然而，为了利用HDC1为作物改良带来的机会，我们需要确切地了解HDC1在分子水平上是如何运作的。例如，HD复合体的组成和其中蛋白质的确切功能在植物中是完全未知的。本项目的目的是研究HDC1在模式植物拟南芥中的分子功能。这项研究将与工业伙伴开展的作物发展计划并行进行。这两个研究计划之间的互惠信息流将确保在模式物种中所取得的基本发现可以立即转化为作物改良。工作方案包括三个部分。在第一个工作包中，我们将使用针对HDC1的抗体来“关联”识别植物蛋白提取物中HDC1-复合体的其他成员。我们将获得一些已鉴定的同源突变株系，并将它们与HDC1突变株系杂交。这项工作将导致对植物中HD复合体的初步了解，并识别限制或增强该复合体中HDC1功能的蛋白质。第二个工作方案涉及HDC1本身是否受到监管以及如何受到监管的问题。特别是，我们将调查HDC1是否是其他激素(串扰)或病原体‘劫持’ABA途径的目标。为此，我们将测量激素和病原体激发子处理过的植物提取物中的HDC1蛋白水平。在第三个工作包中，我们将研究哪些基因导致HDC1对种子萌发和生长的影响--HDC1的“靶标”。首先，我们将使用基因芯片识别野生型和HDC1突变植物中差异表达的所有基因。为了确定HDc1直接靶向的DNA区域，我们将用HDc1抗体下拉与HDc1相关的染色质。最后，我们将用识别乙酰化组蛋白尾巴的抗体来测量染色质的乙酰化水平。这项工作的综合结果将极大地加深我们对植物基因调控的理解，并直接有助于提高作物的产量和水分利用效率。

Climate change and a growing world population are expected to lead to water scarcity and food shortage in the near future. There is an urgent need to increase yield, water usage efficiency and stress tolerance of food crops. We propose to achieve this through controlled manipulation of plant sensitivity to the 'stress' hormone abscisic acid (ABA). The project builds on our recent discovery of a novel gene from Arabidopsis thaliana, which we called 'Histone de-acetylation complex 1' (HDC1). We found that over-expression of HDC1 led to decreased ABA-sensitivity of germinating seeds and to enhanced growth of mature plants, while deletion of HDC1 had the opposite effects. Thus HDC1 can be used as an adjustable 'hormostat'. This property makes HDC1 an attractive target for crop improvement. For example, in a drought-prone rain-fed field increasing ABA-sensitivity will aid plant recovery after dehydration whereas in an irrigated field decreasing ABA-sensitivity could be a means to sustain biomass production with reduced water input. The question is then; how does HDC1 change ABA-sensitivity? Ancestral precursors of HDC1 in yeast are members of large multi-protein complexes that biochemically modify (de-acetylate) histone proteins that are associated with DNA (chromatin). Histone de-acetylation (HD) determines the overall structure of the DNA which in turn exerts a hyper-level of control over gene activity. Our current hypothesis is that HDC1 'titrates' the stability of a chromatin complex thereby modifying accessibility of the DNA to ABA-dependent regulators and hence ABA-sensitivity. This is an exciting concept because it means that via HDC1 one could gain control over a whole suite of stress responses without the need to tinker with the underlying complex signalling network. However, to exploit the opportunities presented by HDC1 for crop improvement we need to understand exactly how HDC1 operates at the molecular level. For example, the composition of HD complexes and the precise functions of proteins therein are completely unknown in plants. The aim of this project is to investigate the molecular function of HDC1 in the model plant Arabidopsis. This research will run in parallel to a crop development programme carried out by the Industrial Partner. Reciprocal information flow between the two research programmes will ensure that fundamental discoveries made in the model species can immediately be translated into crop improvement. The work programme has three parts. In the first work package we will use an antibody against HDC1 to identify 'by association' other members of the HDC1-complex in plant protein extracts. We will obtain mutant lines for some of the identified associates and cross them with the HDC1mutant lines. This work will lead to a first understanding of HD complexes in plants, and to the identification of proteins that limit or enhance HDC1 function within the complex. The second work package addresses the question whether HDC1 itself is regulated and how. In particular, we will investigate whether HDC1 is a target for 'hijacking' of the ABA pathways by other hormones ('cross talk') or by pathogens. For this purpose we will measure HDC1 protein levels in plant extracts treated with hormones and pathogen elicitors. In the third work package we will investigate which genes cause the effects of HDC1 on seed germination and growth - the 'targets' of HDC1. In the first instance we will identify all genes that are differentially expressed in wildtype and HDC1 mutant plants using gene chips. To identify the DNA regions that are directly targeted by HDc1 we will pull-down HDC1-associated chromatin with the HDC1-antibody. Finally, we will measure acetylation levels of the chromatin with antibodies that recognize acetylated histone tails. The combined outcomes from this work will greatly enhance our understanding of gene regulation in plants and directly contribute to improving yield and water usage efficiency in crops.