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MgHog1 regulates dimorphism and pathogenicity in the fungal wheat pathogen Mycosphaerella graminicola
Rahim Mehrabi1, Lute-Harm Zwiers, Maarten A de Waard
1Plant Research International B.V., Wageningen University and Research Centre (WUR), PO. Box 16, 6700 AA, Wageningen, The Netherlands.
Abstract:
The dimorphic ascomycete pathogen Mycosphaerella graminicola switches from a yeastlike form to an infectious filamentous form that penetrates the host foliage through stomata. We examined the biological function of the mitogen-activated protein kinase-encoding gene MgHog1 in M. graminicola. Interestingly, MgHog1 mutants were unable to switch to filamentous growth on water agar that mimics the nutritionally poor conditions on the foliar surface and, hence, exclusively developed by a yeastlike budding process. Consequently, due to impaired initiation of infectious germ tubes, as revealed by detailed in planta cytological analyses, the MgHog1 mutants failed to infect wheat leaves. We, therefore, conclude that MgHog1 is a new pathogenicity factor involved in the regulation of dimorphism in M. graminicola. Furthermore, MgHog1 mutants are osmosensitive, resistant to phenylpyrrole and dicarboximide fungicides, and do not melanize.
Insights
The MgHog1 gene is crucial for Mycosphaerella graminicola to switch to its infectious filamentous form, enabling wheat infection. MgHog1 mutants exhibit impaired growth and reduced pathogenicity.
Area of Science:
- Plant pathology
- Molecular mycology
- Fungal genetics
Background:
- Mycosphaerella graminicola is a dimorphic fungal pathogen infecting wheat.
- The fungus transitions between yeast-like and filamentous forms for host invasion.
- Mitogen-activated protein kinases (MAPKs) are key regulators in fungal development and pathogenicity.
Purpose of the Study:
- To investigate the role of the MgHog1 gene in the dimorphism and pathogenicity of Mycosphaerella graminicola.
- To understand the regulatory mechanisms underlying the yeast-to-filament transition in this wheat pathogen.
Main Methods:
- Gene knockout to create MgHog1 mutants.
- Growth assays on water agar to assess dimorphism.
- In planta cytological analyses to observe host-pathogen interactions.
- Phenotypic characterization of mutants for osmosensitivity, fungicide resistance, and melanization.
Main Results:
- MgHog1 mutants failed to switch to filamentous growth on water agar, exclusively exhibiting yeast-like budding.
- Mutants showed impaired initiation of infectious germ tubes, leading to a complete failure to infect wheat leaves.
- MgHog1 mutants displayed osmosensitivity, resistance to specific fungicides (phenylpyrrole and dicarboximide), and lacked melanization.
Conclusions:
- MgHog1 is a critical pathogenicity factor in Mycosphaerella graminicola, regulating the dimorphic switch.
- The MgHog1 gene is essential for the development of infectious structures and successful wheat leaf colonization.
- MgHog1 influences multiple fungal phenotypes, including stress response and secondary metabolite production.
