Molecular mechanisms of virulence and avirulence in the Avr3a family of Phytophthora.

卵菌是类真菌的真核微生物。若干种卵菌是对世界农业和粮食安全具有重要意义的毁灭性病原体。从本质上讲，这意味着它们破坏了作为重要食物来源的作物。“疫霉”这个词是一个卵菌谱系的属，意思是“植物破坏者”。疫霉物种包括导致爱尔兰马铃薯饥荒的有机体，疫霉（Phytophthora infestans），它会导致一种通常被称为“马铃薯疫病”或“晚疫病”的疾病（它也会导致番茄疫病），以及辣椒疫病（辣椒疫霉）和大豆根腐病（大豆疫霉）。最近，疫霉（Phytophthora ramorum）在英国引起了相当大的关注，因为它正在威胁着橡树等标志性树木。疫霉仍然是最著名的，可以说是最重要的卵菌病原体。它继续使现代农业每年损失数十亿英镑，也影响着发展中国家的自给农业。马铃薯现在是世界上第三重要的作物，因此，致病菌是对全球粮食安全的重要生物威胁。在全球范围内，其他疫霉物种造成的损害也很严重。我们的长期目标是了解卵菌，特别是疫霉，如何成功地感染植物，并解剖受这些病原体影响的植物过程。现在已经确定，像其他病原体一样，疫霉菌也会分泌一些被称为“效应物”的蛋白质，这些蛋白质可以调节植物的免疫反应并使寄主定植。破译效应物的生化活性是理解发病机制的关键。在这些蛋白质中，rxlr型效应物以蛋白质中存在的氨基酸序列命名，靶向植物细胞内部。在本提案中，我们将重点关注在上述疫霉物种中发现的一组特定的RxLR效应物。这些都是Avr3a家族的成员，因为它们与疫霉菌效应物Avr3a具有相同的氨基酸序列同源性。基于我们已经获得的初步数据，我们的目标是确定这些蛋白质在抑制植物免疫系统方面具有哪些保守和不同的功能。通过宿主因子，该蛋白家族的成员也可以在植物中启动程序性细胞死亡反应，以限制病原体的生长。我们还旨在了解这种反应早期发生的一些细节，特别是这些效应物是如何被宿主细胞因子检测到的。这项研究将有助于建立病原体蛋白与植物过程之间的功能联系。详细了解Avr3a家族如何能够操纵植物免疫的某些方面并被其他家族识别，将提高我们对感染过程的理解，并为设计对疫霉病原体的抗性提供新的策略。

The oomycetes are fungus-like eukaryotic microorganisms. Several species of the oomycetes are devastating pathogens that are of great importance to world agriculture and food security. In essence, this means that they destroy crops that are critical sources of food. The word 'Phytophthora', which is a genus with the oomycete lineage means 'plant destroyer'. Phytophthora species include the organism responsible for the Irish potato famine, Phytophthora infestans, which causes a disease commonly know as 'potato blight' or 'late blight' (it also causes tomato blight), as well as pepper blight (Phytophthora capsici) and soybean root rot (Phytophthora sojae). Recently, Phytophthora ramorum has gained considerable press in the UK as it is threatening iconic trees, such as oak. Phytophthora infestans remains the best-known and, arguably, the most important oomycete pathogen. It continues to cost modern agriculture billions of pounds annually and also impacts subsistence farming in developing countries. With potato now ranked the third most important crop in the world, P. infestans is an important biotic threat to global food security. Damage caused by other Phytophthora species is also severe, on a global scale. Our long-term objective is to understand how oomycetes, particularly Phytophthora, successfully infect plants and dissect the plant processes that are affected by these pathogens. It is now well established that, like other pathogens, Phytophthora species secrete a number of proteins, termed 'effectors', that modulate the immune response of plants and enable host colonization. Deciphering the biochemical activities of effectors is critical to understanding mechanisms of pathogenesis. Among these proteins, RxLR-type effectors, named after an amino acid sequence present in the protein, are targeted to the inside of plant cells. In this proposal, we focus on a particular group of RxLR effectors that is found in the Phytophthora species mentioned above. These are all members of the Avr3a family, as they share amino acid sequence homology to the Phytophthora infestans effector Avr3a. Building on preliminary data we have already obtained, we aim to define what conserved and divergent functions these proteins have in suppressing the plant immune system. Through host factors, members of this protein family can also initiate a programmed cell-death response in plants designed to limit pathogen growth. We also aim to understand some details of how early steps in this response occur, specifically how these effectors are detected by host cell factors. This study will help to establish functional connections between pathogen proteins and plant processes. Detailed knowledge of how the Avr3a family is able to manipulate certain aspects of plant immunity and be recognized by others will improve our understanding of the infection process and enable novel strategies for engineering resistance to Phytophthora pathogens.