MPG1, A GENE ENCODING A FUNGAL HYDROPHOBIN OF MAGNAPORTHE-GRISEA, IS INVOLVED IN SURFACE RECOGNITION

Upon encountering a leaf surface, emergent germ tubes from conidia of the rice blast fungus, Magnaporthe grisea, form infection structures c alled appressoria that allow direct penetration of plant cells, The MP G1 gene encodes a fungal hydrophobin of M. grisea that is expressed du ring development of aerial hyphae, conidia; and appressoria, Deletion of MPG1 reduces the efficiency of appressorium formation, We found tha t yeast extract repressed MPG1 expression in vitro and inhibited appre ssorium development of the rice pathogen, strain Guy11. Appressorium f ormation of mpg1 mutants is rescued in trans by coinoculation with wil d-type cells, MPG1 is required for efficient induction of appressoria in response to a host surface or highly hydrophobic artificial substra tes, However, we identified several artificial substrates that can sup port efficient appressorium formation of mpg1 strains, This finding su ggests that Mpg1p is not specifically required for appressorium format ion, but is involved in the interaction with, and recognition of, the host surface, Additionally, a time window of competence to form appres soria was identified; the decision to form appressoria occurs approxim ately 6 to 8 h following conidial germination, After this critical tim e, cells are no longer able to form appressoria in response to inducti ve cues. These studies indicate that MPG1 hydrophobin is required for host recognition and that it acts as a morphogenetic signal for cellul ar differentiation.