Proteome analysis of rice blast fungus (Magnaporthe grisea) proteome during appressorium formation

We used two-dimensional gel electrophoresis (2-DE) to identify the proteins that are induced in the rice blast fungus Magnaporthe grisea during appressorium formation. Proteins were extracted from conidia that had germinated on hydrophilic glass plates or from germinated and appressoria-forming conidia on leaf wax-coated hydrophobic glass plates after 4, 8, and 12 h of incubation. Differentially expressed protein spots during appressorium formation were confirmed from gels after 2-DE analysis where proteins had been labeled with (35)S methionine and stained with silver. Internal amino acid sequencing identified five proteins among several proteins induced during appressorium formation. Two denoted as M. grisea proteasome homolgues (MgP1 and MgP5) were 20S proteasome alpha subunits. The remaining three were scytalone dehydratase (SCD), and serine carboxypeptidase Y (CPY). None of the five have been reported previously in the rice blast fungus apart from SCD. We further investigated the role the alpha subunit of 20S proteasome plays in appressorium formation. We confirmed by Western blot analysis that MgP5 is highly expressed during appressorium formation and found that it is also markedly induced by nitrogen- and carbon-starvation, in particular by the former. These observations suggest that the 20S proteasome may be involved in remobilizing storage proteins, which then help to build the appressorium. Thus, fungal proteome analysis may provide important clues about developmental changes such as the generation of the appressorium.