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MPG1, a gene encoding a fungal hydrophobin of Magnaporthe grisea, is involved in surface recognition
1Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843, USA.
Abstract:
Upon encountering a leaf surface, emergent germ tubes from conidia of the rice blast fungus, Magnaporthe grisea, form infection structures called appressoria that allow direct penetration of plant cells. The MPG1 gene encodes a fungal hydrophobin of M. grisea that is expressed during development of aerial hyphae, conidia, and appressoria. Deletion of MPG1 reduces the efficiency of appressorium formation. We found that yeast extract repressed MPG1 expression in vitro and inhibited appressorium development of the rice pathogen, strain Guy11. Appressorium formation of mpg1 mutants is rescued in trans by coinoculation with wild-type cells. MPG1 is required for efficient induction of appressoria in response to a host surface or highly hydrophobic artificial substrates. However, we identified several artificial substrates that can support efficient appressorium formation of mpg1 strains. This finding suggests that Mpg1p is not specifically required for appressorium formation, but is involved in the interaction with, and recognition of, the host surface. Additionally, a time window of competence to form appressoria was identified; the decision to form appressoria occurs approximately 6 to 8 h following conidial germination. After this critical time, cells are no longer able to form appressoria in response to inductive cues. These studies indicate that MPG1 hydrophobin is required for host recognition and that it acts as a morphogenetic signal for cellular differentiation.
Insights
The MPG1 gene is crucial for the rice blast fungus Magnaporthe grisea to recognize host surfaces and form appressoria, essential infection structures. Its absence impairs this process, impacting fungal pathogenicity.
Area of Science:
- Plant pathology
- Mycology
- Molecular biology
Background:
- Magnaporthe grisea causes rice blast, a devastating plant disease.
- Appressoria are critical infection structures enabling fungal penetration of plant cells.
- The MPG1 gene encodes a hydrophobin involved in appressorium development.
Purpose of the Study:
- To investigate the role of the MPG1 gene in appressorium formation and host interaction.
- To understand the regulation of MPG1 expression and its impact on M. grisea pathogenicity.
- To identify factors influencing appressorium development in mpg1 mutants.
Main Methods:
- Gene deletion and complementation of MPG1 in M. grisea.
- In vitro expression studies using yeast extract.
- Appressorium formation assays on various artificial and host-derived substrates.
- Microscopic observation of fungal development and infection structures.
Main Results:
- Deletion of MPG1 significantly reduced appressorium formation efficiency.
- Yeast extract repressed MPG1 expression and inhibited appressorium development.
- mpg1 mutants showed defects in host surface recognition but could form appressoria on specific artificial substrates.
- A critical time window (6-8 hours post-germination) for appressorium competence was identified.
Conclusions:
- MPG1 hydrophobin is essential for efficient appressorium formation and host surface recognition by M. grisea.
- MPG1 acts as a morphogenetic signal regulating cellular differentiation during infection.
- The findings provide insights into the molecular mechanisms underlying fungal pathogenesis and host-pathogen interactions.