COMPLEMENTATION OF THE MPG1 MUTANT PHENOTYPE IN MAGNAPORTHE-GRISEA REVEALS FUNCTIONAL-RELATIONSHIPS BETWEEN FUNGAL HYDROPHOBINS

The functional relationship between fungal hydrophobins was studied by complementation analysis of an mpg1(-) gene disruption mutant in Magn aporthe grisea, MPG1 encodes a hydrophobin required for full pathogeni city of the fungus, efficient elaboration of its infection structures and conidial rodlet protein production. Seven heterologous hydrophobin genes were selected which play distinct roles in conidiogenesis, frui t body development, aerial hyphae formation and infection structure el aboration in diverse fungal species. Each hydrophobin was introduced i nto an mpg1(-) mutant by transformation. Only one hydrophobin gene, SC I from Schizophyllum commune, was able partially to complement mpg1(-) mutant phenotypes when regulated by its own promoter. In contrast, si x of the transformants expressing hydrophobin genes controlled by the MPG1 promoter (SC1 and SC4 from S. commune, rodA and dewA from Aspergi llus nidulans, EAS from Neurospora crassa and ssgA from Metarhizium an isopliae) could partially complement each of the diverse functions of MPG1, Complementation was always associated with partial restoration o f a rodlet protein layer, characteristic of the particular hydrophobin being expressed, and with hydrophobin surface assembly during infecti on structure formation. This provides the first genetic evidence that diverse hydrophobin-encoding genes encode functionally related protein s and suggests that, although very diverse in amino acid sequence, the hydrophobins constitute a closely related group of morphogenetic prot eins.