Exploiting the Phytophthora infestans genome: targets for sustainable potato protection

作物病原菌侵染是影响农业可持续发展的关键问题，既有病害造成的产量损失，也有杀菌剂的使用对环境的影响。马铃薯是世界第四大作物，马铃薯的卵菌病原菌致病疫霉是最重要的病原。致病疫霉是晚疫病造成的巨大产量损失的罪魁祸首，全球每年与化学防治相关的费用高达300万GB。对致病疫霉的遗传抗性和控制化学物质的部署都取得了有限的成功，因为两者都很容易被病原菌种群的变异所克服。这一建议旨在通过开发致病疫霉基因组来解决现有控制措施所面临的问题，以寻找其致病力武器库中重要和不变的成分，以用于可持续的马铃薯保护。具体地说，这些信息将用于确定马铃薯持久抗病育种的来源，并开发病原菌本质上难以克服的新的控制策略。卵菌包括70多种疫霉，可以说是双子叶植物最重要的病原体。在过去一年左右的时间里，已经从模式植物拟南芥的卵菌病原体、大豆和致病疫霉本身(由SCRI小组)中鉴定出编码触发抗性的蛋白质的基因。这些蛋白质彼此非常不同，除了一个保守的基序，该基序类似于将疟疾毒力蛋白输送到人类血细胞内所需的序列。初步证据表明，这个基序是将卵菌蛋白运送到各自植物宿主的细胞中所必需的。该基序为寻找在宿主细胞内传递的其他蛋白质提供了一个签名，在那里它们可能暴露在防御监视系统中。在这项提案中，我们的目标是从致病疫霉中鉴定出这种蛋白质的全部补体。我们将对这些蛋白质进行表征，以寻找那些对感染至关重要的蛋白质(因此不容易被病原体丢失)，以及那些在不同病原体菌株中显示出很小序列差异的蛋白质(因此似乎处于保持不变的选择压力下)。我们推测，如果能够找到识别它们的抗性，这些蛋白质代表着病原体潜在的阿喀琉斯之跟。为此，我们将在SCRI(英联邦马铃薯收藏馆)的野生马铃薯生物多样性收藏中寻找对这些蛋白具有抗性的植物(因此，即使不是全部，也是对大多数致病疫霉菌株具有抗性)。这些抗性很可能是高度持久的，因此将优先引入SCRI商业支持的育种计划中的栽培马铃薯。我们打算开发的致病疫霉的第二个‘阿喀琉斯’跟腱是这些毒力蛋白在马铃薯细胞内转移所需的机制。易位机制可能是疾病控制的一个非常合适的靶点，因为抑制这一传递过程将阻止效应蛋白进入宿主细胞，从而抑制病原体的正常感染过程。将进行实验，通过鉴定与保守的递送基序结合的蛋白质来寻找负责易位的蛋白质。我们将进行实验，以确定它们是如何工作的。这些与卵菌毒力蛋白传递基序结合的蛋白的模拟物不仅有可能阻止致病疫霉引起感染，而且通过抑制其他卵菌植物病原体而具有更广泛的应用，并可能延伸到无关的病原体，如疟疾。生物技术公司先正达是将利用我们在该项目这方面的发现的最终用户。

Pathogen attack of crop plants is a key issue affecting agricultural sustainability in terms of both yield loss due to disease and environmental impact due to fungicide application. The oomycete pathogen Phytophthora infestans is the most significant pathogen of potato, the world's fourth largest crop. P. infestans is responsible for large yield losses through late blight disease, and costs associated with chemical control amount to £3M globally per year. Genetic resistance to P. infestans and control chemicals have been deployed with limited success, as both have been readily overcome by variation in pathogen populations. This proposal aims to address the problems faced by existing control measures through exploitation of the P. infestans genome to seek vital and invariant components of its pathogenicity arsenal that can be targeted for sustainable potato protection. Specifically, this information will be used to identify sources of durable potato disease resistance for breeding and to develop novel control strategies that are intrinsically difficult for the pathogen to overcome. The oomycetes include more than 70 Phytophthora species and are arguably the most significant pathogens of dicotyledenous plants. In the last year or so, genes have been identified from oomycete pathogens of the model plant Arabidopsis, of soybean, and from P. infestans itself (by the SCRI group), that encode proteins that trigger resistance. These proteins are very different to each other except from a conserved motif that is similar to a sequence required for delivery of malaria virulence proteins inside human blood cells. Preliminary evidence suggests that this motif is required to deliver the oomycete proteins into the cells of their respective plant hosts. The motif has provided a signature to search for other proteins that are delivered inside host cells, where they may be exposed to defence surveillance systems. In this proposal we aim to identify the entire complement of such proteins from P. infestans. We will characterize these proteins to seek those that are essential for infection (and thus are not easily lost by the pathogen) and those that show little sequence variation in diverse strains of the pathogen (and thus appear to be under selective pressure to remain unchanged). We postulate that such proteins represent potential Achilles' Heels for the pathogen if resistances can be found that recognize them. To this end, we will search in a wild potato biodiversity collection at SCRI (The Commonwealth Potato Collection) for plants that are resistant to these proteins (and thus to most, if not all, strains of P. infestans). These resistances are likely to be highly durable and thus will be prioritized for introduction into cultivated potato in commercially supported breeding programmes at SCRI. The second 'Achilles' Heel' of P. infestans that we intend to exploit is the machinery required for translocation of these virulence proteins inside potato cells. The translocation machinery is potentially a very suitable target for disease control, since inhibition of this delivery process would prevent effector proteins entering host cells and thus inhibit the pathogen's normal infection process. Experiments will be conducted to find the proteins responsible for translocation by identifying proteins that bind to the conserved delivery motif. We will conduct experiments to determine how they work. Mimicks of these proteins which bind to the delivery motif in oomycete virulence proteins will potentially not only prevent P. infestans from causing infection but will have a wider application by inhibiting other oomycete plant pathogens and will possibly extend to unrelated pathogens such as malaria. The biotechnology company Syngenta is the end-user that will exploit our findings in this aspect of the project.