MPG1 ENCODES A FUNGAL HYDROPHOBIN INVOLVED IN SURFACE INTERACTIONS DURING INFECTION-RELATED DEVELOPMENT OF MAGNAPORTHE-GRISEA

The rice blast fungus expresses a pathogenicity gene, MPG1, during app ressorium formation, disease symptom development, and conidiation. The MPG1 gene sequence predicts a small protein belonging to a family of fungal proteins designated hydrophobins. Using random ascospore analys is and genetic complementation, we showed that MPG1 is necessary for i nfection-related development of Magnaporthe grisea on rice leaves and for full pathogenicity toward susceptible rice cultivars. The protein product of MPG1 appears to interact with hydrophobic surfaces, where i t may act as a developmental sensor for appressorium formation. Ultras tructural studies revealed that MPG1 directs formation of a rodlet lay er on conidia composed of interwoven similar to 5-nm rodlets, which co ntributes to their surface hydrophobicity. Using combined genetic and biochemical approaches, we identified a 15-kD secreted protein with ch aracteristics that establish it as a class I hydrophobin. The protein is able to form detergent-insoluble high molecular mass complexes, is soluble in trifluoroacetic acid, and exhibits mobility shifts after tr eatment with performic acid. The production of this protein is directe d by MPG1.