Rice blast is the most devastating pathogen of rice worldwide. It is caused by the fungal pathogen Magnaporthe grisea. Crop losses from M. grisea infections have increased in recent years with up to 30 % of the annual rice harvest lost. The spores of M. grisea are covered by a polymeric protein layer with amyloid characteristics which assists with spore attachment to the rice leaf and infection of the plant. This outer amyloid layer is composed of the fungal hydrophobin protein MPG1. Expression of MPG1 is essential for correct formation and maturation of specialised infectious structures known as appressoria and efficient infection. Furthermore, MHP1, another M. grisea hydrophobin, is known to be involved in the production and germination of spores as well as appressorium development, with MHP1 knockouts displaying less infectious growth.
Hydrophobins are a class of small proteins characterised by eight conserved cysteines. The proteins are unique to filamentous fungi that are able to spontaneously self-assemble into an amyloid rodlet monolayer at hydrophobic:hydrophilic interfaces. MPG1 and MHP1 share much sequence homology, in particular, between cysteines 7 and 8, a region shown to be critical for rodlet formation in another hydrophobin. We have developed conditions for the recombinant expression and purification of MPG1 and MHP1. We are investigating the structure and characteristics of these two proteins with a range of biophysical techniques. In addition, site-directed mutagenesis will be used to identify residues in these proteins that are critical for self-association and to understand the mechanism of rodlet assembly. Our aim is to develop inhibitors of rodlet assembly and/or rodlet:rice leaf interactions that will be used to interfere with the air-borne spread of M. grisea spores and infection of rice.