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

卵菌是一种类似真菌的真核微生物。有几种卵菌是毁灭性的病原体，对世界农业和粮食安全非常重要。从本质上说，这意味着它们摧毁了作为关键食物来源的农作物。‘疫霉’这个词是一个带有卵菌血统的属，意思是‘植物破坏者’。疫霉种类包括导致爱尔兰土豆饥荒的微生物--致病疫霉，它会引起一种通常被称为‘土豆疫病’或‘晚疫病’的疾病(它也会引起番茄疫病)，以及辣椒疫病(疫霉)和大豆根腐病(疫霉大豆疫霉)。最近，疫霉在英国获得了相当大的报道，因为它威胁到了标志性的树木，如橡树。致病疫霉仍然是最广为人知的，也可以说是最重要的卵菌病原体。它继续每年给现代农业造成数十亿英镑的损失，并影响发展中国家的自给自足农业。马铃薯现已成为世界第三大粮食作物，致病疫霉对全球粮食安全构成重要的生物威胁。在全球范围内，其他疫霉物种造成的破坏也很严重。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，并剖析受这些病原体影响的植物过程。现在公认的是，像其他病原体一样，疫霉可以分泌一系列被称为“效应器”的蛋白质，来调节植物的免疫反应并使其能够在宿主上定居。破译效应器的生化活动对于理解发病机制至关重要。在这些蛋白质中，RxLR型效应器，以蛋白质中存在的一个氨基酸序列命名，针对植物细胞内部。在这项建议中，我们重点关注在上述疫霉物种中发现的一组特定的RxLR效应器。这些都是AVR3a家族的成员，因为它们与致病疫霉效应器AVR3a的氨基酸序列同源。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，这个蛋白质家族的成员还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。我们还打算了解这种反应的早期步骤是如何发生的一些细节，特别是这些效应器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菌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人识别，将提高我们对感染过程的理解，并使新的策略能够对疫霉病原体产生工程抗性。

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.