Understanding the mechanism of chloroplast immunity.

我们下一代面临的“重大挑战”之一是确保全球粮食安全。这可以通过提高生产力和选择对变化的环境条件反应强烈的植物相结合来实现。如果没有定制的本地育种解决方案，提高生产力是一项挑战，这反映在通过传统育种实现的平均年作物产量不断下降。生物胁迫造成的作物损失对产量损失的贡献不成比例，通常约占作物产量损失的四分之一，但在极端情况下超过四分之三。因此，如果我们要切实确保到2050年能够养活估计的90亿人口，就必须发展新的方法来限制作物的病原体感染，从而提高产量。我们最近的研究表明，叶绿体是决定植物与微生物相互作用最终结果的关键战场。除了固定碳的能力，叶绿体在整合多种环境刺激和感知植物代谢状态方面发挥着核心作用。叶绿体作为活性氧的主要来源，是大量初级碳代谢和大多数激素代谢前体合成的场所，是病原体操纵的主要目标。我们的开创性工作表明，叶绿体通过产生活性氧（ROS）的爆发来响应保守病原体基序（非自我）的识别，我们认为这是一种防御信号。因此，成功的病原体传递蛋白质和被称为效应器的小分子来干预这一过程并不奇怪。我们的数据表明，细菌和真菌病原体通过重新配置核编码植物基因的表达来实现这一目标，一些效应物甚至进入叶绿体。这些效应物通过抑制光合作用（可以说是地球上最重要的反应之一）来阻止活性氧的爆发，但我们不知道是如何做到的。我们所知道的是，效应物会增加一种叫做脱落酸（ABA）的激素的产生，而停止ABA的产生会使植物更具抗性。相反，添加ABA阻止叶绿体ROS爆发，使病原体生长。在这里，我们的主要目标是了解非自体识别如何激活叶绿体免疫，以及病原体效应蛋白如何进化以抑制这种免疫。一个主要目标是在引起疾病或诱导防御的治疗过程中对叶绿体的生物物理变化进行详细研究。我们将观察在这些处理过程中叶绿体内蛋白质的变化以及小分子的变化。结合这些数据，我们将预测有助于这些过程的蛋白质。为了了解它们在防御中的作用，我们将改变它们的数量，并观察这些植物对病原体的反应。我们还会计算出有多少效应器，以及这些效应器的功能性质，进入叶绿体。第二个主要工作是可视化从健康植物到患病植物过渡期间叶绿体和细胞核中ROS产生的动态。我们也对细胞内的细胞器在疾病和防御促进挑战中的行为感兴趣。为了可视化，我们用荧光标记标记了细胞中的不同细胞器，我们将使用这些标记来监测它们在感染过程中的行为。由于叶绿体免疫似乎是保守的，我们的长期目标是利用从这些研究中获得的知识进行新的重组或干预策略，从而为植物提供抗病原体的广谱抗性。

One of the "big challenges" for our next generation is to ensure global food security. This can be achieved through a combination of increasing productivity and selecting for plants which respond robustly to changing environmental conditions. Increasing productivity is challenging without bespoke local breeding solutions and this is reflected in the ever decreasing average annual crop yields achieved through conventional breeding. Crop losses due to biotic stress contribute disproportionately to yield losses, often around one quarter but in extreme cases in excess of three quarters of a crop. Thus developing novel approaches to restricting pathogen infections of crops and consequently yields must be a primary objective if we are to realistically ensure we can feed the estimated 9 billion people by 2050. We have recently shown that the chloroplast is a key battlefield in determining the eventual outcome of plant-microbe interactions. Aside from its ability to fix carbon, chloroplasts play a central role in integrating multiple environmental stimuli and sensing the metabolic status of the plant. As a principal source of reactive oxygen species, the site of a significant amount of primary carbon metabolism and synthesis of the majority of hormone metabolic precursors, the chloroplast represents a prime target for pathogen manipulation. Our pioneering work has shown that the chloroplast responds to recognition of conserved pathogen motifs (non-self) by generating a burst of reactive oxygen species (ROS) that we believe act as a defensive signal. It is not surprising therefore that successful pathogens deliver proteins and small molecules known as effectors - to intervene in this process. Our data indicate that pathogens, both bacterial and fungal, achieve this by reconfiguring expression of nuclear encoded plant genes and some effectors actually even enter the chloroplast. These effectors stop the ROS burst by suppressing photosynthesis - arguably one of the most important reactions on this planet - but we don't know how. What we do know is that effectors increase the production of a hormone called abscisic acid (ABA), and stopping ABA production makes the plant more resistant. Conversely, adding ABA stops the chloroplast ROS burst, enabling pathogen growth. Here our primary objective is to understand how recognition of non-self activates chloroplast immunity and how pathogen effector proteins have evolved to suppress this immunity. One major objective is to undertake detailed studies of the biophysical changes in the chloroplast during treatments that cause disease or induce defence. We will look at the changes in proteins within chloroplasts during these treatments and changes in the small molecules as well. Merging these data we will predict proteins that contribute to these processes. To access their role in defence we will change their abundance and looking at how those plants behave to pathogens. We will also work out how many effectors, and the functional nature of those effectors, enter the chloroplast. A second major strand of work is to visualise the dynamics of ROS production in the chloroplast and the nucleus during the transition from healthy to diseased plants. We are also interested in how organelles within the cell behave during disease and defence promoting challenges. To visualise this we have labelled different organelles in the cell with fluorescent markers and we will use these to monitor their behaviours during the infection process.As chloroplast immunity appears conserved, our longer term goal is to use the knowledge gained from these studies in novel re-engineering or intervention strategies that will provide plants with broad spectrum resistance against pathogens.