Nick Talbot, University of Exeter

Combating the Cereal Killer: Investigating the Biology of Rice Blast Disease

Rice blast is one of the most serious diseases affecting global rice production and each year destroys enough rice to feed 60 million people. Rice blast is caused by the fungus Magnaporthe oryzae, which is also the causal agent of wheat blast, a disease that now threatens wheat production in South America and South Asia. My research group is investigating the biology of plant infection by the blast fungus and using this information to develop new strategies to control blast diseases. During plant infection, M. oryzae forms a specialised infection structure called an appressorium. The infection cell generates enormous turgor, of up to 80 atmospheres, which is focused as mechanical force to breach the rice cuticle and enable entry of the fungus into plant tissue. Appressorium function depends on precise cell cycle control and autophagic recycling of the contents of the fungal spore into the developing infection cell. Re-polarisation of the appressorium requires a hetero-oligomeric septin GTPase complex that organises a toroidal F-actin network at the base of the appressorium. This allows protrusion of a rigid penetration hypha to invade epidermal cells, enabling the fungus to colonise rise tissue and cause disease. Once tissue is invaded the fungus undergoes differential expression and secretion of a large repertoire of effector proteins that can be directed into plant cells to suppress plant immunity. The fungus then uses primary pit fields to move from cell-to-cell within the host plant. We have identified key determinants of appressorium function and tissue colonisation, which are potential targets for disease intervention. We are also using knowledge of the population dynamics of the rice blast fungus to guide marker-assisted plant breeding strategies in Sub-Saharan Africa to provide more durable combinations of disease resistance genes into high yielding, locally adapted rice cultivars. I will present an overview of the biology of plant infection by the rice blast fungus, recent progress in understanding fungal pathogenicity, and describe how this knowledge is being utilised to guide disease control strategies.