Determining the mechanism of septin-mediated plant infection by the rice blast fungus Magnaporthe oryzae

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The aim of this project is to understand how rice plants succumb to a very serious disease called rice blast. Each year, rice blast disease destroys up to 30% of the global rice harvest and causes serious epidemics in Sub-Saharan Africa, South-East Asia and South America. It is therefore a continuing threat to global food security. Rice blast is caused by a fungus called Magnaporthe oryzae and this project aims to determine how the fungus infects rice plants. The rice blast fungus produces a specialised infection structure called an appressorium, which generates enormous pressure (up to 8MPa, or 40 times the pressure of a car tyre) and to apply physical force at the leaf surface to puncture the plant cuticle. In this way the fungus can invade leaf tissue and cause disease. We aim to investigate how pressure inside the appressorium is translated into physical force at the base of the infection cell. We have discovered that a group of protein called septins, are essential for the appressorium to puncture the rice cuticle. Their role is to re-model the cell's internal cytoskeleton so it applies force at the leaf surface and forms a penetration peg that enter the leaf. This project will investigate how septins assemble at the base of the appressorium and how this region of the cell becomes specialised to secrete proteins into plant cells, how the appressorium develops a penetration peg, and how the fungus then rapidly invades the leaf. We will characterise how septin assembly is regulated and, in particular, how the fungus is able to monitor the turgor pressure within the appressorium and determine the optimal point (or trigger) for penetration peg development. We will also determine how this process is regulated in concert with the cell division cycle of the fungus, allowing the plant infection process to be controlled effectively.When considered together, the objectives of this research project will provide new insight into the biology of plant infection by one of the most important crop diseases in the world today. This information will be used to inform new disease control strategies that are urgently required. In addition to the global significance of rice blast, knowledge gained from the project will also be of value to UK agriculture because many of the most serious diseases that affect our major cereal crops, barley and wheat, share a similar infection mechanism. Disease control strategies emerging from this work are therefore likely to be of broad spectrum for the most important cereal diseases, such as rusts and powdery mildews in addition to rice blast.