Confocal Laser Scanning Microscopy to Investigate Cellular Dynamics in Host-Pathogen Interactions

Two of the major global challenges for the next century will be how to ensure global food security and how to contend with emerging diseases which threaten ecosystem health. It emerges that fungi are a major threat to mankind, as no other group of pathogens are more deadly to crop plants than fungi. Fungal disease accounts for persistent crop losses of 10-12% each year and substantially higher losses in epidemic years. Consequently, fungal diseases decimate our harvests and cause widespread malnutrition and starvation. The burden of disease is increasing as global climate change hastens the geographic spread and the variety of plants infected.

The University of Exeter has established itself as a centre of fungal-related plant disease research excellence. Our quest is to better understand the intimacy of the relationship between rice, maize and wheat and their respective fungal pathogens, as these crops occupy some 40% of our global crop-land. We will provide technical knowledge from our work on the rice blast fungus Magnaporthe oryzae, the wheat pathogen Mycosphaerella graminicola and the maize smut fungus Ustilago maydis to gain a better insight into the dynamic exchanges between fungi and their hosts at the interface where they first find conflict. Exeter University currently provides many technical facilities to support their research and to meet this challenge. However, lacking is high-end equipment that allows fast, sensitive live-cell imaging of the pathogen in infected plant tissue. In recent years, this technology has enabled plant-pathologists in the EU to investigate the communication between host plant and the invading pathogen. In this application we seek support to purchase a modern confocal laser scanning microscopy, which will complement the existing facilities at the Exeter Bioimaging Centre.

Fungal pathogens are responsible for significant crop yield losses and therefore pose a serious challenge to food security and social stability in many countries. The economic losses caused by fungal plant pathogens exceeds that of viruses, nematodes, bacteria and protozoa combined.

A hot-spot of modern research in plant pathology is the host-pathogen interface, where local secretion of effectors and cell wall modulators helps the fungus to overcome / suppress the plant defence system. Confocal laser scanning microscopy has proven to be of particular use for visualization of fluorescently-labelled effectors, which are released into the plant cell and modulate its defence system or its development. How these effectors are delivered within the fungal cell and how are they taken up by the host is not clear. Furthermore, whilst the fungal cell wall is instrumental in masking the fungus from triggering plant innate immunity, the sites of fungal wall modification and the pathways and mechanisms of delivery of wall modifying enzymes remains elusive. This application seeks funds to purchase a modern Leica TCS SP8 confocal laser scanning microscope to (a) investigate the delivery of effectors within the fungal pathogen, (b) analyse the dynamic behaviour of fungal cell wall modifying enzymes and (c) elucidate the role of endocytosis in effector uptake at the host-pathogen interface. The new instrument will be part of the Bioimaging Centre. As such, it will be accessible to additional users and, therefore, will significantly improve the local research infrastructure at Exeter.

The Royal Society report (2009) Pollock report (2013) and UK AgriTech strategy report (July 2013) highlight the huge challenge of ensuring global food security over the next five decades. Crop yields must rise, but chemical inputs must fall. Novel approaches to improve productivity by protecting our crops from disease merit much attention. None of this is possible, with regards to crop disease, without insight and detailed description of the dynamic exchange at the host-pathogen interface.

The impact of our proposed work is therefore very significant on the world's stage with regard to Food Security but it will impact beyond plant disease, being relevant to human mycoses and emerging fungal diseases affecting ecosystems security. Our work will draw together the disciplines of plant disease biology, food security, ecosystem health, cell movement dynamics and effector biology

Our work will impact upon:

i) Knowledge - giving a greater understanding of the earliest moments of fungal effector synthesis and delivery.
ii) UK science - enhancing the profile of the Investigators on the national and international stage.
iii) Interdisciplinary science - endowing the Investigators with new awareness and widened interdisciplinary skills.
iv) Fostering broadened industrial links with Syngenta.
v) Fuelling greater research effort across the continents.
vi) Enhancing skills of Bioimaging officer and training new staff and students.
vii) Promoting public awareness of science and raising awareness of importance of pathogenic fungi to the plight of the hungry.