The Conserved MAP Kinase MpkB Regulates Development and Sporulation without Affecting Aflatoxin Biosynthesis in
Sang-Cheol Jun1, Jong-Hwa Kim1, Kap-Hoon Han1
1Department of Pharmaceutical Engineering, Woosuk University, Wanju 55338, Korea.
Abstract:
In eukaryotes, the MAP kinase signaling pathway plays pivotal roles in regulating the expression of genes required for growth, development, and stress response. Here, we deleted the mpkB gene (AFLA_034170), an ortholog of the Saccharomyces cerevisiae FUS3 gene, to characterize its function in Aspergillus flavus, a cosmopolitan, pathogenic, and aflatoxin-producing fungus. Previous studies revealed that MpkB positively regulates sexual and asexual differentiation in Aspergillus nidulans. In A. flavus, mpkB deletion resulted in an approximately 60% reduction in conidia production compared to the wild type without mycelial growth defects. Moreover, the mutant produced immature and abnormal conidiophores exhibiting vesicular dome-immaturity in the conidiophore head, decreased phialide numbers, and very short stalks. Interestingly, the ΔmpkB mutant could not produce sclerotia but produced aflatoxin B1 normally. Taken together, these results suggest that the A. flavus MpkB MAP kinase positively regulates conidiation and sclerotia formation but is not involved in the production of secondary metabolites such as aflatoxin B1.
Insights
The Aspergillus flavus MpkB MAP kinase is crucial for producing spores and sclerotia. Deleting the mpkB gene significantly reduced spore production and altered conidiophore development, but did not affect aflatoxin B1 levels.
Area of Science:
- Molecular Biology
- Mycology
- Fungal Genetics
Background:
- Mitogen-activated protein kinase (MAPK) pathways regulate vital cellular processes in eukaryotes.
- MpkB, a homolog of Saccharomyces cerevisiae FUS3, is known to influence differentiation in Aspergillus species.
- Aspergillus flavus is a significant pathogen and producer of aflatoxins.
Purpose of the Study:
- To investigate the function of the mpkB gene in Aspergillus flavus.
- To understand the role of MpkB in fungal development and secondary metabolite production.
Main Methods:
- Gene deletion of mpkB in Aspergillus flavus.
- Phenotypic analysis of the mpkB deletion mutant (ΔmpkB).
- Assessment of conidia production, conidiophore morphology, sclerotia formation, and aflatoxin B1 levels.
Main Results:
- mpkB deletion caused a ~60% reduction in conidia production without affecting mycelial growth.
- The ΔmpkB mutant exhibited abnormal conidiophores with immature vesicle domes, fewer phialides, and shorter stalks.
- Sclerotia formation was abolished in the ΔmpkB mutant, while aflatoxin B1 production remained normal.
Conclusions:
- Aspergillus flavus MpkB positively regulates conidiation and sclerotia formation.
- MpkB is not essential for the production of aflatoxin B1 in A. flavus.
- MpkB plays a specific role in fungal development distinct from secondary metabolite biosynthesis.
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