MPG1 is a small (112 aa precursor) secreted, cysteine-rich class I hydrophobin of the rice blast fungus Magnaporthe oryzae (Pyricularia oryzae). After removal of its signal peptide and formation of four intramolecular disulphide bonds, which are required for secretion but not for aggregation, the protein is exported to the cell surface. At hydrophobic:hydrophilic interfaces it self-assembles into functional amyloid rodlets that associate laterally into an amphipathic monolayer; in vivo this forms the interwoven ~5 nm rodlet layer of the conidial wall and also coats aerial hyphae and appressoria, conferring surface hydrophobicity (mpg1 mutants are "easily wettable"). MPG1 is strongly expressed during conidiation, nutrient starvation, appressorium formation and lesion development. Loss of MPG1 reduces conidiation, weakens SDS-resistant attachment of germlings to hydrophobic surfaces, and lowers the efficiency of appressorium induction on host and highly hydrophobic surfaces (a defect rescued by exogenous cAMP or by co-inoculation with wild-type spores), resulting in reduced virulence on rice. The assembled coat is thought to mediate recognition of the hydrophobic host surface, and in vitro MPG1 rodlet coatings retain active cutinase 2 on hydrophobic surfaces. MPG1 has no known enzymatic activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005199 structural constituent of cell wall | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the class I hydrophobin domain. MPG1 self-assembles into amyloid rodlets that form the outermost hydrophobic rodlet layer of the conidial wall; this is a structural, non-catalytic contribution to the fungal cell surface. Reason: The rodlet layer on conidia depends on MPG1 and is composed of MPG1-type class I hydrophobin rodlets (PMID:12239409; PMID:27142249). Structural constituent of cell wall is the standard and appropriate MF for class I hydrophobins (the same mapping is applied to A. fumigatus and A. nidulans RodA and S. commune SC3), and there is no more specific MF term for rodlet-forming hydrophobins. This is the core molecular function. Supporting Evidence: PMID:12239409 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. PMID:27142249 The spores of M. oryzae are covered with a layer composed of the hydrophobin MPG1 and the protein is also present in appressoria PMID:27142249 We show that MPG1 self-assembly into functional amyloid rodlets is strictly limited to a hydrophobic:hydrophilic interface. |
| GO:0005576 extracellular region | EXP PMID:12239409 MPG1 Encodes a Fungal Hydrophobin Involved in Surface Intera... | ACCEPT | Summary: Talbot et al. 1996 identified a 15-kD secreted MPG1-dependent protein with class I hydrophobin properties. Reason: Directly supported: the protein is secreted (signal peptide; recovered from the extracellular milieu and the conidial surface). Fungal-type cell wall/spore wall are more specific locations for the assembled form, but secretion to the extracellular region is correct and experimentally grounded. Supporting Evidence: PMID:12239409 we identified a 15-kD secreted protein with characteristics that establish it as a class I hydrophobin. |
| GO:0005576 extracellular region | EXP PMID:15773983 Four conserved intramolecular disulphide linkages are requir... | ACCEPT | Summary: Kershaw et al. 2005 showed by immunolocalization that wild-type Mpg1 is secreted to the cell surface whereas cysteine-to-alanine variants self-assemble but are not secreted. Reason: Immunolocalization of wild-type versus disulphide-deficient variants directly establishes secretion of MPG1 to the cell surface. Abstract-only cache, but the abstract states the localization result explicitly. Supporting Evidence: PMID:15773983 Immunolocalization revealed that Mpg1 hydrophobin variants, lacking intact disulphide bonds, retain the capacity to self-assemble, but are not secreted to the cell surface. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | ACCEPT | Summary: Automated mapping from UniProt subcellular location "Secreted". Reason: Consistent with the experimental EXP annotations (PMID:12239409, PMID:15773983); redundant but correct. Supporting Evidence: PMID:12239409 we identified a 15-kD secreted protein with characteristics that establish it as a class I hydrophobin. |
| GO:0009277 fungal-type cell wall | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the class I hydrophobin domain. Assembled MPG1 forms the outer rodlet layer of the conidial wall and coats aerial hyphae and appressoria. Reason: Supported for MPG1 specifically: the 2005 study concerns secretion and cell wall localization of Mpg1, and the conidial rodlet layer depends on MPG1. The more specific spore wall location is proposed separately as NEW. Supporting Evidence: PMID:15773983 Four conserved intramolecular disulphide linkages are required for secretion and cell wall localization of a hydrophobin during fungal morphogenesis. PMID:12239409 MPG1 directs formation of a rodlet layer on conidia composed of interwoven ~5-nm rodlets |
| GO:0031160 spore wall | IDA PMID:12239409 MPG1 Encodes a Fungal Hydrophobin Involved in Surface Intera... | NEW | Summary: MPG1 forms the rodlet layer covering conidia; loss of MPG1 abolishes the conidial rodlet layer and complementation restores it. Reason: The conidium is the best-documented in vivo site of assembled MPG1. Comparator check: the orthologous-role class I hydrophobins A. fumigatus RodA (P41746) and A. nidulans RodA (P28346) both carry GO:0031160 spore wall by EXP/IDA, so this is the GO convention for conidial rodlet hydrophobins rather than a novel claim. Supporting Evidence: PMID:12239409 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. PMID:27142249 The spores of M. oryzae are covered with a layer composed of the hydrophobin MPG1 |
| GO:0042243 asexual spore wall assembly | IMP PMID:12239409 MPG1 Encodes a Fungal Hydrophobin Involved in Surface Intera... | NEW | Summary: MPG1 is itself the self-assembling building block of the conidial rodlet layer; the layer is absent in mpg1 mutants and restored by complementation. Reason: Participation test: MPG1 does the work of this assembly step - it is the structural subunit that self-assembles into amyloid rodlets at the hydrophobic:hydrophilic interface (PMID:27142249), not merely a regulator required for it. Comparator check: A. nidulans RodA (P28346) carries GO:0042243 asexual spore wall assembly by IMP for the equivalent rodlet-layer defect. Broader process terms suggested by mutant phenotypes (conidium formation, appressorium formation, pathogenesis) are deliberately not proposed, as they rest on necessity evidence only. Supporting Evidence: PMID:12239409 Ultrastructural studies revealed that MPG1 directs formation of a rodlet layer on conidia composed of interwoven ~5-nm rodlets PMID:27142249 We show that MPG1 self-assembly into functional amyloid rodlets is strictly limited to a hydrophobic:hydrophilic interface. file:PYRO7/MPG1/MPG1-deep-research-falcon.md Loss-and-rescue ultrastructure establishes MPG1 as a determinant of the hydrophobic conidial rodlet layer. |
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Download this section (compressed HTML)Q: Is the appressorium-induction defect of mpg1 mutants due to MPG1 acting as a surface-sensing signal, or secondarily to impaired adhesion/surface contact of germ tubes? The trans-rescue by co-inoculated wild-type spores and the cAMP bypass are compatible with either; should process terms such as appressorium formation (GO:0075016) be annotated to MPG1 at all, given that only necessity evidence exists?
Q: Does MPG1 recruit or retain cutinase 2 (Cut2) on the rice leaf surface in vivo, or is the in vitro retention of Cut2 activity on MPG1 coatings non-specific?
Q: What are the respective, non-redundant roles of MPG1 and the class II hydrophobin MHP1 in conidial coat assembly and infection?
Experiment: Germling adhesion and appressorium induction assays of mpg1 mutants on surfaces of graded hydrophobicity with and without pre-coating by purified recombinant MPG1 rodlets, to separate a structural/adhesive role from a signalling role.
Experiment: In planta co-localization of tagged MPG1 and Cut2 at the appressorium-leaf interface, and Cut2 activity measurement on leaves inoculated with wild type versus mpg1.
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