MPG1 Encodes a Fungal Hydrophobin Involved in Surface Interactions during Infection-Related Development of Magnaporthe grisea

Abstract

The rice blast fungus expresses a pathogenicity gene, MPG1, during appressorium 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 analysis and genetic complementation, we showed that MPG1 is necessary for infection-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 it may act as a developmental sensor for appressorium formation. Ultrastructural studies revealed that MPG1 directs formation of a rodlet layer on conidia composed of interwoven ~5-nm rodlets, which contributes to their surface hydrophobicity. Using combined genetic and biochemical approaches, we identified a 15-kD secreted protein with characteristics 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 treatment with performic acid. The production of this protein is directed by MPG1.

Inactivation of the mitogen-activated protein kinase Mps1 from the rice blast fungus prevents penetration of host cells but allows activation of plant defense responses

“…Although we do not know which gene products could be activated by this pathway in M. grisea, it is known that, for emergent growth and sporulation, filamentous fungi secrete a group of fungal cell-wall proteins, called hydrophobins, that are arrayed on the outer cell-wall surface (27). Interestingly, the hydrophobin Mpg1p from M. grisea has been shown to be necessary for sporulation and pathogenicity (16,17). It will be interesting to see whether developmental expression of Mpg1p depends on Mps1 signaling.…”

“…Growth, mating assays, transformation, and nucleic-acid extraction from M. grisea were performed as described (16)(17)(18). Infection assays on rice, epidermal-cell penetration assays on onions, germination assays, and appressorium-formation assays were performed as described (18,19).…”

Structural and Functional Role of the Disulfide Bridges in the Hydrophobin SC3

“…This results in a dramatic drop of the water surface tension, enabling fungi to breach the interface to form aerial reproductive structures (2). Hydrophobins also provide these aerial structures with a hydrophobic coating (1) and mediate attachment of fungi to hydrophobic surfaces (for example, in pathogenic interactions) (3,4).…”

Assembly of the Fungal SC3 Hydrophobin into Functional Amyloid Fibrils Depends on Its Concentration and Is Promoted by Cell Wall Polysaccharides

“…By stabilizing the SC3 coating at a hydrophobic solid, schizophyllan is expected to function in hyphal attachment. Hydrophobin-mediated attachment is important in fungal pathogenic interactions (29) and probably also in mutual beneficial interactions (1).…”