Exploiting the Phytophthora infestans genome: targets for sustainable potato protection

从病害造成的产量损失和使用杀菌剂造成的环境影响两方面来看，农作物的病原菌攻击是影响农业可持续性的关键问题。马铃薯是世界第四大作物，卵菌致病菌疫霉是马铃薯最重要的致病菌。由于晚疫病，致病菌造成了大量的产量损失，全球每年用于化学防治的费用高达300万英镑。对感染假单胞菌的遗传抗性和控制化学品的部署取得了有限的成功，因为两者都很容易被病原体种群的变化所克服。本研究旨在通过利用病原菌基因组，寻找病原菌致病库的重要和不变成分，解决现有控制措施所面临的问题，这些成分可用于马铃薯的可持续保护。具体来说，这些信息将用于确定马铃薯持久抗病育种的来源，并制定新的控制策略，这些策略本质上是难以克服病原体的。卵菌包括70多种疫霉，可以说是双子叶植物中最重要的病原体。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寄生假单胞菌本身（由SCRI小组）中鉴定出了编码引发抗性的蛋白质的基因。这些蛋白彼此之间有很大的不同，除了一个保守的基序，这个基序类似于在人血细胞内传递疟疾毒力蛋白所需的序列。初步证据表明，该基序是将卵菌蛋白传递到各自植物寄主细胞中所必需的。该基序提供了一种特征，可以用来寻找宿主细胞内的其他蛋白质，这些蛋白质可能暴露在防御监视系统中。在这个提议中，我们的目标是鉴定这些蛋白质的整个补体从P. infestans。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少序列变化的蛋白质（因此似乎处于选择压力下保持不变）。我们假设，如果能找到识别它们的抵抗力，这些蛋白质就代表了病原体潜在的致命弱点。为此，我们将在SCRI （The Commonwealth potato collection）的野生马铃薯生物多样性收集中寻找对这些蛋白质具有抗性的植物（从而对大多数（如果不是全部的话）P. infestans菌株具有抗性）。这些抗性很可能具有很高的持久性，因此将在SCRI商业支持的育种计划中优先引入栽培马铃薯。我们打算利用的第二个“阿喀琉斯之踵”是马铃薯细胞内这些毒力蛋白易位所需的机制。这种转运机制可能是疾病控制的一个非常合适的靶标，因为抑制这种转运过程可以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。实验将通过鉴定与保守传递基序结合的蛋白质来寻找负责易位的蛋白质。我们将进行实验来确定它们是如何起作用的。这些蛋白的模拟物与卵菌毒力蛋白中的传递基元结合，可能不仅可以防止疟原虫引起感染，而且可以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，将利用我们在项目这方面的发现。

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.