Type III Effector suppression of basal defense and activation of ABA signalling.

植物部署了一个非常复杂的协同防御策略网络，统称为基础防御或非宿主抗性。这些防御屏障中的许多是代谢物，其单独或协同作用以防止病原体进入。然而，细菌确实成功地侵入了植物。它们通过化学或蛋白质性质的多种毒力因子的活性获得成功。我们知道细菌将30-40种蛋白质注入植物细胞，这些“效应”蛋白质操纵宿主转录和蛋白质表达，以协调复杂的信号事件网络。一般来说，这些信号传导事件有两个结果，（i）抑制或逃避宿主防御和（ii）操纵宿主代谢以提供病原体增殖的营养。我们感兴趣的是这些入侵策略的分子机制。也就是说，病原体是如何利用如此少量的蛋白质来克服植物防御的。这些都是主要问题，因为疾病可以占全球作物产量的20%以上。为了最初解决这个问题，我们使用了一种全局基因谱分析技术，使我们能够在任何一个时间点定量植物中所有基因的表达。我们研究了一个时间界定的感染系列。通过适当的控制和广泛的生物信息学分析和文献研究，我们能够突出显示大量可能与病原体克服防御能力相关的基因。这种方法使我们确定了一组先前已知的保护植物免受水分胁迫的基因。这些基因中的许多涉及植物激素脱落酸（阿坝）的生物合成和反应途径。我们进一步研究了这些线索使用阿坝信号通路的突变体和直接激素测量质谱法的组合。我们的研究使我们得出了压倒性的结论，即感染性细菌操纵植物阿坝激素途径以提高毒性。由于水的可利用性与成功的细菌发病机制密切相关，因此这种策略提供了一种强有力的手段，可以在受感染的组织中选择已建立的宿主应激信号通路以促进毒力。我们现在寻求进一步的资金，以建立在这些目前未发表的细菌效应器在抑制植物防御和建立疾病状态的作用机制的见解。这些数据迫使我们重新评估不同激素在感染过程中的相互作用。由于植物激素信号可能最终通过几个中心成分控制，一种途径的干扰可能会对另一种途径的生物活性产生不利影响。换句话说，可能是其他激素的补偿性变化实际上是观察到的效果的原因。从工业的角度来看，重要的是要准确地量化改变植物激素途径将对作物生产力产生的影响。阿坝是一种特征鲜明的应激激素;因此，该项目将研究突变体对病原体的激素反应，并对阿坝不敏感或过敏的受感染植物进行基因分析实验。在平行实验中，我们将产生表达（i）报告基因融合体的转基因植物，所述报告基因融合体被设计成允许我们可视化感染过程的动态。我们还将产生转基因植物，表达通常被细菌效应子抑制的报告基因。这些植物将用于遗传筛选，以确定参与抑制基础防御的关键调节因子。这项工作的长期成果将是更好地了解病原体如何成功地克服宿主防御。这些结果将为未来的策略提供信息，这些策略旨在操纵植物反应，以开发对病原体的广谱免疫力。

Plants deploy of an extraordinary complex network of synergistic defensive strategies, collectively termed basal defense or non-host resistance. Many of these defensive barriers are metabolites which act individually or cooperatively prevent pathogen ingress. However, bacteria do successfully invade a plant. They achieve their success from activities of a variety of virulence factors, of a chemical or proteinaceous nature. We know bacteria inject a collection of 30-40 proteins into the plant cell and these 'effector' proteins manipulate host transcription and by definition protein expression, to orchestrate a complex network of signaling events. Broadly speaking, these signaling events have two outcomes, (i) suppression or evasion of host defenses and (ii) manipulation of host metabolism to provide nutrients for pathogen multiplication. We are interested in the molecular mechanisms underpinning these invasion strategies. That is, how do pathogens overcome plant defenses using such a small collection of proteins. These are major issues as disease can account for over 20% of crop yields worldwide. To initially address this issue we used a technique of global gene profiling that allowed us to quantitate the expression of all the genes in the plant at any single time point. We examine a time-delimited infection series. With the appropriate controls and extensive bioinformatics analyses and literature research we were able to highlight a large number of genes that could be associated with the ability of the pathogen to overcome defense. This approach led us to identify a set of genes that were previously known to protect plants from water stress. Many of these genes were implicated in the biosynthesis and response pathways of the plant hormone abscisic acid (ABA). We further investigated these leads using a combination of mutants in ABA signaling pathways and direct hormone measurement using mass spectrometry. Our research led us to the overwhelming conclusion that infectious bacteria manipulate plant ABA hormone pathways to promote virulence. As water availability is strongly correlated with successful bacterial pathogenesis, this strategy provides a powerful means of co-opting established host stress signalling pathways in infected tissues to promote virulence. We now seek further funding to build on these current unpublished to establish a mechanistic insight into the role of bacterial effectors in suppressing plant defense and establishing the disease state. These data compel us to re-evaluate the interaction of different hormones in the infection process. As plant hormone signaling is probably ultimately controlled through a few central components, perturbation of one pathway may adversely effect the biological activity of another. In other words, it may be compensatory changes in other hormones that are actually causal to the observed effect. From an industrial perspective it is important to accurately quantitate what impact modifying plant hormonal pathways will have on crop productivity. ABA is a well characterised stress hormone; therefore The project will investigate hormonal responses to pathogens in mutants, and develop gene profiling experiments with infected plants that are insensitive or hypersensitive to ABA. In parallel experiments we will generate transgenic plants expressing (i) reporter fusions designed to allow us to visualize the dynamics of the infection process. We will also generate transgenic plants expressing a reporter that is normally suppressed by bacterial effectors. These plants will be used in a genetic screen to identify key regulators involved in suppression of basal defense. The long-term outcome of this work will be better understanding of how pathogens successfully overcome host defenses. These results will inform future strategies aimed toward manipulating plant responses to develop broad spectrum immunity to pathogens.