MPG1, a Gene Encoding a Fungal Hydrophobin of Magnaporthe grisea, Is Involved in Surface Recognition. Janna L Beckerman. Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843 U.S.A. Daniel J. Ebbole. Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843 U.S.A. MPMI 9:450-456. Accepted 5 April 1996. Copyright 1996 The American Phytopathological Society.

Upon encountering a leaf surface, emergent germ tubes from conidia of the rice blast fungus, Magnaporthe grisea, form infection structures called appressoria that allow direct penetration of plant cells. The MPGI gene encodes a fungal hydrophobin of M. grisea that is expressed during development of aerial hyphae, conidia, and appressoria. Deletion of MPGI reduces the efficiency of appressorium formation. We found that yeast extract repressed MPGI expression in vitro and inhibited appressorium development of the rice pathogen, strain Guyll. Appressorium formation of mpgl mutants is rescued in trans by coinoculalion with wild-type cells. MPGI is required for efficient induction of appressoria in response to a host surface or highly hydrophobic artificial substrates. However, we identified several artificial substrates that can support efficient appressorium formation of mpgl strains. This finding suggests that Mpglp is not specifically required for appressorium formation, but is involved in the interaction with, and recognition of, the host surface. Additionally, a time window of competence to form appressoria was identified; the decision to form appressoria occurs approximately 6 to 8 h following conidial germination. After this critical time, cells are no longer able to form appressoria in response to inductive cues. These studies indicate that MPGI hydrophobin is required for host recognition and that it acts as a morphogenetic signal for cellular differentiation