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.
Highlights
Aspergillus section Flavi consists of 27 species, and Aspergillus flavus is a representative species that shows the characteristics of the section Flavi well [1,2]
To further confirm for this, we examined the number of conidiophores formed in the mycelial ball during submerged culture and found that more conidiophores were produced in the ∆mpkB mutant than in the wild type
S. cerevisiae Fus3/Kss1 that is associated with conidiation, conidiophore morphogenesis, sclerotiogenesis, and aflatoxin biosynthesis
Summary
Aspergillus section Flavi consists of 27 species, and Aspergillus flavus is a representative species that shows the characteristics of the section Flavi well [1,2]. A. flavus is a cosmopolitan saprophytic soil fungus that infects grain (e.g., maize, and wheat), peanuts, and fruit crops, causing the crops to rot and damaging their productivity [5,6]. A. flavus and Aspergillus parasiticus are known to produce mycotoxins including aflatoxin B1 and B2, which are considered the most potent carcinogens in nature [7,8,9]. Consumption of aflatoxin-contaminated crops and feeds by humans or livestock can lead to liver disease, liver cancer, acute physiological disorders, and death [9,10]. A. flavus is an opportunistic pathogenic fungus that causes invasive or noninvasive aspergillosis in humans and animals along with Aspergillus fumigatus [11,12]
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