Phytophthora infestans effector PexRD54 associates with host Rab GTPase Rab8-1 to reprogram endomembrane transport

Filamentous plant pathogens are a group of eukaryotic pathogens including oomycete genus Phytophthora, as well as rust fungi, and Powdery mildew fungi, which cause most destructive plant diseases and threaten global food security. These pathogens cost billions of dollars annual looses to modern agriculture and severely impact subsistence agriculture in developing countries. These microorganisms are accommodated within the host cells through specialized cellular structures. However, little is known about molecular mechanisms underlying microbial accommodation inside the plant cells. The proposed research aims to characterize the host processes required for accommodation of filamentous plant pathogens inside the plant cells with a specific focus on illustrating the role of plant endomembrane transport system in this process. Among the oomycetes, Phytophthora spp. cause some of the most destructive plant diseases in the world and cause enormous economic damage to important crop species such as potato, tomato, and soybean, as well as environmental damage in natural ecosystems. Phytophthora infestans, the Irish potato famine pathogen, which causes late blight of potato and tomato, is one of the most important biotic threats to global food production leading to worldwide economic losses exceeding $5 billion annually. Unfortunately, late blight of potato is a reemerging destructive disease, which caused severe epidemics in potato farms across the UK lately. Our long-term objective is to dissect the molecular mechanisms underlying plant cell autonomous immunity and the role of endomembrane traffic in this process by particularly using P. infestans as a model pathogen. Like some other filamentous pathogens that form destructive plant diseases, P. infestans is accommodated inside the host cells by forming specialized compartments termed haustoria, which are separated from the invaded plant cells by newly synthesized host derived membranes with unknown origin and composition. This interface is critical for development of parasitic infection by enabling efficient macromolecule exchange. Therefore, understanding the regulation of macromolecule exchange processes at host pathogen interface is critical to develop novel strategies to engineer disease resistance in plants. Unfortunately, despite being discovered decades ago, our current knowledge about haustoria is limited. Deciphering the cellular and biochemical activities at this interface is critical for understanding the mechanisms of pathogenesis. Like other pathogens, P. infestans secretes a battery of proteins, termed effectors that suppress plant immunity and enable parasitic infection. Recently we discovered that some of these effectors specifically accumulate at the host pathogen interface inside the infected plant cells. In this study we aimed to identify host components of focal immunity using one such effector, termed PexRD54, as a molecular probe. Our preliminary work unraveled that around haustoria, PexRD54 associated with a host protein named Rab8-1, a member of Rab GTPases family of eukaryotic vesicle trafficking regulators. Our goal is to functionally characterize PexRD54 and Rab8-1 in order to establish the roles of these molecules at host pathogen interface. This study will help to establish functional characterization of plant endomembrane transport processes perturbed by pathogens and help understanding the origin, function and composition of the host pathogen interface. In turn, a detailed knowledge of PexRD54 manipulation of Rab8-1 will improve our understanding of the microbial accommodation inside the plant cells and will allow for creating renewed opportunities for engineering disease resistance in crops.

Some filamentous plant pathogens associate with plant cells through specialized infection structures termed haustoria to deliver effector proteins or uptake nutrients. Haustorium is separated from the plant cell by a host-derived membrane known as the extrahaustorial membrane (EHM), with unknown origin and composition. Plant cells generally respond to pathogen penetration with a spatially confined cell-autonomous immune response known as focal immunity. Unfortunately, despite the documented importance of haustoria formation and focal immunity, our current knowledge in these processes is limited. These processes have been difficult to dissect using standard genetic approaches due to overlap between focal immunity and plant development. Pathogen secreted effectors accumulating around haustoria (perihaustorial effectors) provided an excellent alternative to study focal immunity. In addition to the reported P. infestans perihaustorial effectors, we identified a novel perihaustorial effector named PexRD54. By deploying PexRD54 as a molecular probe, we identified a host Rab GTPase that accumulated at the EHM named Rab8-1. The overall aim of this proposal is to determine how PexRD54 accumulates at haustoria and modulates host endomembrane transport by targeting Rab8-1. We will use genetic, biochemical, and cell imaging methods to functionally characterize PexRD54 and Rab8-1 association and elucidate their role in immunity. This research program is both timely and innovative because little is known about molecular mechanisms underlying microbial accommodation inside the plant cells. At the end of this study, we expect to dissect a unique type of effector targeted vesicle transport process and identify clues for the biogenesis and function of the EHM. The proposed research will uncover basic knowledge in endomembrane transport systems by assigning molecular functions to key regulators of this process and shed light on the microbial accommodation inside the plant cells.

Plant diseases directly impact global food security, one of the most important problems for growing human population. While many people in developing countries suffer from starvation and related diseases, food prizes gradually increase in developed countries. Filamentous plant pathogens cause the most devastating plants diseases and lead to vast economic losses on important crop species as well as environmental damage in natural ecosystems. Among the oomycetes, Phytophthora spp. cause some of the most destructive plant diseases in the world and are arguably the most devastating pathogens of dicot plants. Phytophthora species cause enormous economic damage to important crop species such as potato, tomato, and soybean, as well as environmental damage in natural ecosystems. The most notable species is Phytophthora infestans, the Irish potato famine pathogen, which causes late blight of potato and tomato causing worldwide potato production losses exceeding $5 billion annually, making P. infestans one of the most important biotic threats to global food production. Currently, management of plant diseases such as the late blight disease is mainly achieved by applications of chemicals, some of which are likely to be banned in the near future. Understanding the biology of host colonization by P. infestans and other filamentous pathogens is not only critical for improving genetic control that can replace chemical control of plant diseases, but also for devising innovative disease management strategies and maintaining healthy natural ecosystems. The proposed project will shed light on the unknown nature of the role of endomembrane transport in plant immunity. This will address one of the major unknowns in this scientific field, and lead to the creation of novel strategies for manipulating plants towards resistance to filamentous pathogens. Such knowledge will also contribute to the leadership of the UK in the scientific field of molecular plant pathology. Consequently, we expect that our research proposal will potentially have an impact on non-academic units such as plant biotechnology corporates, the agricultural society, and policy makers.
The PI will manage the impact plan. The plan will be revised at monthly project meetings. Data generated will be publicly released in line with the BBSRC policy on data sharing. We will ensure the maximum availability of the data and resources produced to allow for investigation and exploitation by others. PI has excellent track record in communicating the output of his research to a broad audience and experienced at writing scientific articles. Data generated in this proposal will be made publicly available via open access publishing where it does not interfere with potential exploitation, as well as via presentations at various national/international meetings. In addition, Imperial College has an extensive series of Open Days and Summer Schemes for schools organized by the Outreach department (imperial.ac.uk/outreach) where PI can regularly presenting his research outcomes. Postdoctoral researcher will be encouraged to develop his communication skills within both the academic and non-academic community in order to better understand the wider impact of his research.
Imperial Innovations Group provides technology commercialisation services and technology development funding for Imperial College London academic staff. We will use Imperial Innovations to engage with industrial partners concerning any commercialization of our research. This will ensure rapid translation of cutting-edge fundamental discoveries into practical solutions and assist global improvement of agriculture. The PI will oversee the impact activities and will seek the assistance of other project members as well as expert staff at The Imperial College, when necessary. Relevant offices at Imperial College will be involved whenever impact activities include technology transfer or outreach/press releases.