Exploiting the Phytophthora infestans genome to identify gene targets for sustainable potato protection

农作物的病原体侵袭是影响农业可持续性的关键问题，因为病害导致产量损失和杀菌剂施用造成的环境影响。马铃薯是世界第四大农作物，卵菌病原致病疫霉是马铃薯最重要的病原菌。致病疫霉是导致晚疫病造成大量产量损失的原因，全球每年与化学防治相关的成本高达300万英镑。对致病疫霉和控制化学品的遗传抗性已经部署，但成功有限，因为两者都很容易被病原体种群的变异所克服。该提案旨在通过利用致病疫霉基因组来解决现有控制措施所面临的问题，以寻找其致病性武器库中可用于可持续马铃薯保护的重要和不变的组分。具体而言，这些信息将被用来确定持久的马铃薯抗病育种的来源，并制定新的控制策略，本质上是难以克服的病原体。卵菌纲包括70多种疫霉属，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、大豆的卵菌病原体和致病疫霉本身（由SCRI小组）中鉴定出了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，该基序类似于在人类血细胞内递送疟疾毒力蛋白所需的序列。初步的证据表明，这个基序是需要提供卵菌蛋白到各自的植物宿主的细胞。该基序提供了一个签名，以搜索在宿主细胞内传递的其他蛋白质，在那里它们可能暴露于防御监视系统。在本提案中，我们的目标是从致病疫霉中鉴定此类蛋白质的完整补体。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）和那些在病原体的不同菌株中几乎没有序列变异的蛋白质（因此似乎处于保持不变的选择压力下）。我们假设，如果能够发现识别这些蛋白质的抗性，那么这些蛋白质代表了病原体的潜在致命弱点。为此，我们将在SCRI（英联邦马铃薯保藏中心）的野生马铃薯生物多样性保藏中心中寻找对这些蛋白质具有抗性的植物（因此对大多数（如果不是全部）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。我们打算利用的致病疫霉的第二个“阿喀琉斯之踵”是这些毒力蛋白在马铃薯细胞内移位所需的机制。易位机制可能是疾病控制的非常合适的靶标，因为抑制该递送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。将进行实验以通过鉴定与保守的递送基序结合的蛋白质来找到负责易位的蛋白质。我们将进行实验以确定它们是如何工作的。与卵菌毒性蛋白中的递送基序结合的这些蛋白质的模拟物将不仅潜在地防止致病疫霉引起感染，而且通过抑制其它卵菌植物病原体而具有更广泛的应用，并且可能扩展到不相关的病原体如疟疾。生物技术公司先正达是最终用户，将评估我们的研究结果在该项目的这一方面的使用。

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 evaluate the use of our findings in this aspect of the project.