IDENTIFICATION AND CHARACTERIZATION OF MPG1, A GENE INVOLVED IN PATHOGENICITY FROM THE RICE BLAST FUNGUS MAGNAPORTHE-GRISEA

Differential cDNA cloning was used to identify genes expressed during infectious growth of the fungal pathogen Magnaporthe grisea in its hos t, the rice plant. We characterized one of these genes, MPG1, in detai l. Using a novel assay to determine the proportion of fungal biomass p resent in the plant, we determined that the MPG1 transcript was 60-fol d more abundant during growth in the plant than in culture. Mpg1 mutan ts have a reduced ability to cause disease symptoms that appears to re sult from an impaired ability to undergo appressorium formation. MPG1 mRNA was highly abundant very early in plant infection concomitant wit h appressorium formation and was also abundant at the time of symptom development. The MPG1 mRNA was also expressed during conidiation and i n mycelial cultures starved for nitrogen or carbon. MPG1 potentially e ncodes a small, secreted, cysteine-rich, moderately hydrophobic protei n with the characteristics of a fungal hydrophobin. Consistent with th e role of the MPG1 gene product as a hydrophobin, Mpg1 mutants show an ''easily wettable'' phenotype. Our results suggest that hydrophobins may have a role in the elaboration of infective structures by fungi an d may fulfill other functions in fungal phytopathogenesis.