This study, led by Professor Shihua Wang at Fujian Agriculture and Forestry University, identified the bZIP transcription factor AflHapX in Aspergillus flavus by searching its genome with the HapX protein sequence from Aspergillus fumigatus. To characterize its biological functions, the research team constructed gene deletion and complementary strains using homologous recombination.
The researchers discovered that AflHapX is critical for A. flavus's adaptive response to both iron excess and iron starvation. When equal amounts of conidia from the wild-type (WT), gene deletion mutant (ΔAflhapX), and complemented strain (ΔAflhapXC) were inoculated on YES medium and cultured for seven days at 29 °C, the ΔAflhapX strain produced significantly less aflatoxin B1 (AFB1) than both the WT and complemented strains, as quantified by thin-layer chromatography (TLC).
Notably, when WT and ΔAflhapX strains were cultured under iron-sufficient, iron-starvation, and iron-excess conditions, an intriguing pattern emerged. The ΔAflhapX strain produced more AFB1 under iron sufficiency than under iron starvation, but less than under iron excess. The WT strain exhibited the opposite relationship between iron concentration and AFB1 production, suggesting that AflHapX regulates AFB1 biosynthesis through the iron homeostasis pathway.
Further phenotypic analyses showed that deleting AflhapX increased sclerotium formation and heightened sensitivity to oxidative stress reagents, including H2O2, menadione sodium bisulfite (MSB), and diamide. On peanut seeds, the ΔAflhapX strain produced fewer conidia and less AFB1 compared to the WT and complemented strains.
To gain a genome-wide perspective, the team performed transcriptome profiling of the WT and ΔAflhapX strains. RNA-seq data revealed that AflHapX globally regulates genes involved in iron homeostasis, aflatoxin biosynthesis, and oxidative stress responses at the transcriptional level.
"These findings demonstrate that AflHapX serves as a key regulator coupling iron availability and AFB1 biosynthesis in A. flavus", says Professor Wang. "Our study provides new insights into the interplay between environmental iron and mycotoxin production and may have implications for understanding the regulatory mechanisms of aflatoxin contamination in agricultural products".
The possibility that a single transcription factor coordinates both iron homeostasis and secondary metabolism has important implications for developing novel strategies to control aflatoxin contamination. By targeting the iron-sensing pathway, it may be possible to reduce AFB1 production in A. flavus during crop storage and processing. This research lays the foundation for future efforts to explore the cross-regulation between nutrient sensing and toxin biosynthesis in other pathogenic fungi worldwide.
See the article:
bZIP transcription factor AflHapX coordinates iron homeostasis and aflatoxin biosynthesis in Aspergillus flavus
DOI LinK:
https://doi.org/10.1080/21501203.2026.2720999
