Membrane Biogenesis and Protein Targeting in Haustorium-invaded Plant Cells

植物是非光合生物的最终食物来源。许多致病真菌和卵菌都有一个叫做吸器的取食器官，用来从寄主植物中吸取营养。这些病原体引起广泛和/或毁灭性的作物疾病，如小麦白粉病和锈病、马铃薯晚疫病和橡树猝死，在世界范围内造成巨大的作物损失和树木损害。近年来，人们对植物免疫的分子机制有了更多的了解。然而，防御反应是如何在宿主-病原体界面上执行的，人们知之甚少。模式植物拟南芥（表皮细胞）和白粉病（吸器）之间的相互作用为解决这一具有挑战性的问题提供了一个方便的单细胞系统。该项目利用一种专门针对植物-真菌界面的拟南芥抗性蛋白作为一种独特的工具来研究界面膜的形成，这种形成如何与免疫信号和蛋白质运输相结合，从而在特定的亚细胞位点实现防御。该项目的新信息将有助于阐明宿主-微生物界面膜形成和活动的基本细胞生物学原理，并为控制吸器形成病原体引起的植物疾病的新干预策略提供新的见解。宿主-病原体相互作用的结果取决于吸体外膜（EHM），即宿主-病原体界面。然而，EHM的起源和生物发生以及宿主-病原体在这个界面上的分子相互作用在很大程度上是未知的。该项目的长期目标是了解EHM的生物发生及其在宿主防御和真菌发育中的作用。这些研究人员已经证明(i)来自拟南芥的宿主抗性(R)蛋白RPW8是专门针对EHM的，它通过一种未知的机制激活吸器靶向防御；（ii） RPW8含有两个被认为是ehm靶向所必需的基本残基富集基序。因此，RPW8可以作为一个独特的工具来了解宿主在EHM处的防御，EHM的起源和生物发生，以及侵染宿主细胞在吸器发育过程中以EHM为导向的蛋白运输。具体来说，这个项目有三个主要目标。目的1阐述了在rpw8介导和对吸器形成病原体的基础抗性过程中，过氧化氢是如何在宿主-病原体界面产生和积累的。目标2的重点是表征一种特殊的蛋白质（SNARE）复合物，该复合物参与ehm导向的囊泡运输。目的3研究EHM的生物发生及其在宿主防御和真菌发病中的作用。在化学遗传分析和最先进的共聚焦成像的辅助下，将采用组合的正向和反向遗传学方法来实现上述三个特定目标。该项目获得的新的重要知识将极大地促进我们对植物与吸器形成病原体之间的细胞生物学和分子相互作用的理解，这将有助于未来设计新的策略来控制这些病原体引起的植物疾病。调查人员还将继续制作有关其工作的短片，以便传播和用于教学。

Plants are the ultimate food source for non-photosynthetic organisms. Many pathogenic fungi and oomycetes develop a feeding organ named the haustorium to extract nutrients from host plants. Such pathogens cause widespread and/or devastating crop diseases such as wheat powdery mildew and rust, potato late blight and sudden oak death, resulting in huge crop losses and tree damages worldwide. In recent years, much has been learnt about the molecular mechanisms concerning plant immunity. However, how defense responses are executed at host-pathogen interfaces is poorly understood. Interactions between the model plant Arabidopsis (epidermal cell)and Powdery mildew (haustorium) provides a convenient single-cell system for addressing this challenging question. The project utilizes an Arabidopsis resistance protein that is specifically targeted to the plant-fungal interface as a unique tool to investigate the formation of the interfacial membrane, how that formation is coupled to immune signaling and protein trafficking to enable defense execution at specific subcellular sites. New information from this project should help elucidate the fundamental cell biology principles governing formation of and activities at host-microbe interfacial membranes, and yield new insight into novel intervention strategies to control plant diseases caused by haustorium-forming pathogens. The outcome of the host-pathogen interaction is determined at the extra-haustorial membrane (EHM), the host-pathogen interface. However, both the origin and biogenesis of the EHM and the molecular host-pathogen interactions at this interface are largely unknown. The long-term goal of this project is to understand the biogenesis of the EHM and its role in host defense and fungal development. These investigators have shown that (i) a host resistance (R) protein named RPW8 from Arabidopsis is specifically targeted to the EHM where it activates haustorium-targeted defenses via an unknown mechanism; and that (ii) RPW8 contains two putative basic residue-enriched motifs essential for EHM-targeting. Therefore, RPW8 can be used as a unique tool to understand the host defense at the EHM, the origin and biogenesis of the EHM, and the EHM-oriented protein trafficking in the invaded host cell during haustorial development. Specifically, there are three major aims for this project. Aim 1 addresses how hydrogen peroxide is produced and accumulated in the host-pathogen interface during RPW8-mediated and basal resistance against haustorium-forming pathogens. Aim 2 is focused on characterization of a special protein (SNARE) complex that is engaged in the EHM-oriented vesicle trafficking. Aim 3 investigates EHM biogenesis and its role in host defense and fungal pathogenesis. A combinatory forward and reverse genetics approach, aided by chemical genetic assays and state-of-the-art confocal imaging will be employed to achieve the above three specific objectives. Novel and important knowledge from this project will significantly advance our current understanding of the cell biology and molecular interaction between plants and haustorium-forming pathogens, which should help design new strategies to control plant diseases caused by such pathogens in the future. The investigators will also continue to produce short videos of their work that can be disseminated and used for teaching.