Selective chemical regulation of plant metabolism with herbicide safeners

在小麦、玉米和水稻等主要谷类作物中，安全剂与除草剂一起使用，以加强其选择性除草。这是通过安全子通过上调作物中相应基因的表达来增加除草剂解毒蛋白的表达来实现的。最近，我们已经确定，安全剂以物种特有的方式发挥作用，每种作物对特定类别的安全化学物质做出反应。我们还确定，安全剂的作用不仅限于除草剂解毒蛋白，还延伸到对内源植物新陈代谢的微妙修改，特别是通过改变酚类和硫醇抗氧化剂的产生。因此，安全剂是生物活性的合成化合物，能够选择性地对植物新陈代谢的元素进行重新编程，这些元素在对抗化学物质和/或氧化损伤造成的胁迫方面非常重要。虽然人们在代谢反应水平上部分了解了更安全的作用机制，但植物如何识别这些合成化学物质来启动特定的细胞信号事件，却一无所知。根据化学原理，我们认为现代安全剂可以分为三大类反应性，所有这些反应性都将导致蛋白质表面反应性残基的选择性共价修饰。我们认为，调节蛋白的这种修饰会导致它们的活性或相互作用发生变化，从而启动信号通路，导致编码抗氧化蛋白的基因选择性激活。该计划的目标是利用合成化学和生物化学相结合的方法来识别哪些信号蛋白被选择性地标记为安全剂。这将需要合成标记有识别标签的安全子，然后使用这些“化学挂钩”来识别目标蛋白质，从而确定这些化学物质如何选择性地干预植物生物化学。我们将集中精力在模式植物拟南芥中识别这些初始结合事件，在我们研究的植物中，拟南芥是唯一对所有三类更安全的化学物质都有选择性反应的植物。使用不同的合成策略，化学探针将被设计成在蛋白质提取物和整个植物中发挥作用，然后使用基于质谱学的方法从它们的序列中识别标记的蛋白质。作为该计划的一部分，我们将通过确定敲除这些蛋白的表达对它们对三种测试化学物质的反应的影响，来确认这些蛋白在拟南芥安全物质识别中的作用。我们还将确定是否在谷物中标记类似的蛋白质，以证实我们在农业重要物种中的结果，并开发现有安全分子的化学变体，以确定这如何影响它们在拟南芥和作物物种中选择性增强抗氧化反应。在我们的跨学科方案结束时，我们将首次确定一组重要的农用化学品如何在植物中发挥其选择性作用。确定除草剂的行动地点对于确定新一代的安全者具有改进的活动以确保今后在作物保护中高效和可持续地使用除草剂具有重要意义。此外，了解安全剂的工作原理将使我们能够扩大它们在促进其他植物对化学和氧化应激的抵抗力方面的使用，这些植物有可能在生物修复受污染的土地上应用。

Safeners are used in conjunction with herbicides in major cereal crops such as wheat, maize and rice to enhance their selective weed control. This is achieved by the safeners acting to increase the expression of herbicide detoxifying proteins by up-regulating the expression of the respective genes in the crop. Recently, we have determined that safeners work in a species specific manner, with each crop responding to a specific class of safener chemistry. We have also determined that the effects of safeners are not restricted to herbicide detoxifying proteins, but extend to a subtle modification of endogenous plant metabolism, notably through altering the production of phenolics and thiol antioxidants. Safeners are therefore bioactive synthetic compounds which are able to selectively reprogramme elements of plant metabolism which are important in counteracting stress caused by chemicals and/or oxidative damage. While the mechanism of safener action is partly understood at the level of the metabolic responses, nothing is known as to how these synthetic chemicals are recognised by plants to initiate specific cellular signalling events. Based on chemical principles, we propose that modern safeners can be grouped into three major classes of reactivity, all of which will lead to the selective covalent modification of reactive residues on the surface of proteins. We propose that such modification of regulatory proteins causes changes in their activity or interactions which initiate signalling pathways leading to the selective activation of genes encoding antioxidant proteins. The objectives of this programme are to use a combination of synthetic chemistry and biochemistry to identify which signalling-proteins become selectively labelled with safeners . This will entail synthesising safeners labelled with recognition tags and then using these 'chemical hooks' to identify the proteins targeted, thereby identifying how these chemical selectively intervene in plant biochemistry. We will concentrate our efforts on identifying these initial binding events in the model plant species Arabidopsis thaliana, which uniquely among the plants we have studied is selectively responsive to all three classes of safener chemistry. Using different synthetic strategies, the chemical probes will be designed to work in protein extracts and in whole plants, with the tagged proteins then identified from their sequence using methods based on mass spectrometry. As part of the programme we will confirm the roles of these proteins in safener-recognition in Arabidopsis by determining the effect of knocking-out their expression on their responses to the three chemistries under test. We will also determine whether or not similar proteins become labelled in cereals to confirm our results in agriculturally important species and develop chemical variants of existing safeners to determine how this affects their selective enhancement of antioxidant responses in Arabidopsis and the crop species. At the conclusion of our interdisciplinary programme we will have determined for the first time how an important group of agrochemicals exert their selective action in plants. Defining their site of action has important implications in identifying new generations of safeners with improved activities to ensure the future efficient and sustainable use of herbicides in crop protection. In addition, understanding how safeners work will allow us to extend their use in promoting resistance to chemical and oxidative stress in other plants which has potential for applications in bioremediating contaminated land.