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.

The β-1,3-Exoglucanase GeneexgA(exg1) ofAspergillus oryzaeIs Required to Catabolize Extracellular Glucan, and Is Induced in Growth on a Solid Surface

“…22,23) Secretory production of hydrophobin and cutinase has been implicated in infection by plantpathogenic fungi. [22][23][24][25] The hydrophobin ortholog RolA and the cutinase ortholog CutL1 have been reported in A. oryzae, and were found to function in plant surface interaction. 26,27) The expression of the rolA and cutL1 genes in A. oryzae was analyzed in culture on the filter membrane and onion inner skin.…”

Self-assembly of functional, amphipathic amyloid monolayers by the fungal hydrophobin EAS

“…These proteins are extremely surface active and lower the surface tension of the aqueous growth medium, allowing hyphae to break through the surface and to produce aerial structures (5,6). Many of these aerial structures subsequently become coated with amyloid rodlets, creating a hydrophobic layer that serves multiple purposes, including conferring water resistance to spores for easier dispersal in air (7), preventing wetting or collapse of gas transfer channels (8), enhancing adherence to waxy surfaces such as leaves during infection of rice plants by Magnaporthe grisea (9), and mediating evasion of the immune system as is observed in Aspergillus fumigatus infections (10).…”

Parallels in Fungal Pathogenesis on Plant and Animal Hosts

“…For instance, mutations in hydrophobin MHP1 have pleotropic effects on fungal morphogenesis, including reductions in conidiation, spore germination, and appressorium formation and infectious growth (44), while mutations in hydrophobin MPG1, which has about 20% sequence similarity to MHP1, significantly reduce appressorium formation on the host but not on other surfaces. Conidial germination and infectious growth are not altered (79). Hydrophobins in conidial walls protect the animal pathogen A. fumigatus from being killed by macrophages during initial invasion events (62).…”

“…The surfaces of many fungal spores are covered by a rodlet layer consisting of molecules including hydrophobins, which are low-molecular-weight, cysteine-rich, hydrophobic proteins. In plant pathogens such as M. grisea, particular hydrophobins are needed for a variety of processes during infection (44,79). For instance, mutations in hydrophobin MHP1 have pleotropic effects on fungal morphogenesis, including reductions in conidiation, spore germination, and appressorium formation and infectious growth (44), while mutations in hydrophobin MPG1, which has about 20% sequence similarity to MHP1, significantly reduce appressorium formation on the host but not on other surfaces.…”