The epigenetic reader SntB was identified as an important transcriptional regulator of growth, development, and secondary metabolite synthesis in Aspergillus flavus. However, the underlying molecular mechanism is still unclear. In this study, by gene deletion and complementation, we found SntB is essential for mycelia growth, conidial production, sclerotia formation, aflatoxin synthesis, and host colonization. Chromatin immunoprecipitation sequencing (ChIP-seq) and RNA sequencing (RNA-seq) analysis revealed that SntB played key roles in oxidative stress response of A. flavus, influencing related gene activity, especially catC encoding catalase. SntB regulated the expression activity of catC with or without oxidative stress, and was related to the expression level of the secretory lipase (G4B84_008359). The deletion of catC showed that CatC participated in the regulation of fungal morphogenesis, reactive oxygen species (ROS) level, and aflatoxin production, and that CatC significantly regulated fungal sensitive reaction and AFB1 yield under oxidative stress. Our study revealed the potential machinery that SntB regulated fungal morphogenesis, mycotoxin anabolism, and fungal virulence through the axle of from H3K36me3 modification to fungal virulence and mycotoxin biosynthesis. The results of this study shed light into the SntB-mediated transcript regulation pathways of fungal mycotoxin anabolism and virulence, which provided potential strategy to control the contamination of A. flavus and its aflatoxins.

As a filamentous pathogenic fungus with high-yield of aflatoxin B₁, Aspergillus flavus is commonly found in various agricultural products. It is crucial to develop effective strategies aimed at the prevention of the contamination of A. flavus and aflatoxin. Hexokinase AfHxk1 is a critical enzyme in fungal glucose metabolism. However, the role of AfHxk1 in A. flavus development, aflatoxin biosynthesis, and virulence has not yet been explored. In this study, afHxk1 gene deletion mutant (ΔafHxk1), complementary strain (Com-afHxk1), and the domain deletion strains (afHxk1^ΔD1 and afHxk1^ΔD2) were constructed by homologous recombination. Phenotype study and RT-qPCR revealed that AfHxk1 upregulates mycelium growth and spore and sclerotia formation, but downregulates AFB₁ biosynthesis through related classical signaling pathways. Invading models and environmental stress analysis revealed that through involvement in carbon source utilization, conidia germination, and the sensitivity response of A. flavus to a series of environmental stresses, AfHxk1 deeply participates in the regulation of pathogenicity of A. flavus to crop kernels and Galleria mellonella larvae. The construction of domain deletion strains, afHxk1^ΔD1 and afHxk1^ΔD2, further revealed that AfHxk1 regulates the morphogenesis, mycotoxin biosynthesis, and the fungal pathogenicity mainly through its domain, Hexokinase_2. The results of this study revealed the biological role of AfHxk1 in Aspergillus spp., and might provide a novel potential target for the early control of the contamination of A. flavus.

Aspergillus flavus and its secondary metabolites aflatoxins pose a significant threat to the health of humans, animals, and plants. Therefore, there is an urgent need to control A. flavus contamination. AfverB plays a key role in the aflatoxin gene cluster; however, its function and mechanism in fungal development and virulence remain poorly understood. In this study, we constructed afVerB gene deletion mutants (∆afVerB−1 and ∆afVerB−2) and two CYP domain mutants (afVerB^∆D1 and afVerB^∆D2) through homologous recombination. Phenotype analysis revealed that, via its two CYP domains, AfVerB is deeply involved in fungal morphogenesis and aflatoxin synthesis. Insect and crop colonization models revealed that AfVerB plays a key role in the fungus’s ability to infect hosts, and stress experiments discovered that AfVerB plays a significant role in the response to various environmental stresses, which explains why AfVerB is a key factor in fungal infection to some extent. RT-qPCR analysis demonstrated that AfVerB performs its bio-function through corresponding regulatory factors. We ultimately discovered that AfVerB is deeply involved in cell membrane stress stability, thereby participating in the regulation of fungal drug resistance (sensitive to AMB and resistant to VOR in this study). The CYP domain of AfVerB, particularly its second CYP domain, is crucial for the execution of its biological functions. This study elucidated the regulatory mechanisms by which AfVerB regulates fungal pathogenicity and aflatoxin biosynthesis, providing potential strategies for controlling A. flavus and its aflatoxin contamination.

Aspergillus flavus Link, 1809 is a pathogenic fungus widely present in the environment. It can infect plants and also acts as an opportunistic pathogen affecting humans and other animals. The aflatoxins (AFs), it produces, can cause cancers such as liver cancer. Therefore, in-depth research into the pathogenic mechanisms of A. flavus is crucial. Arp8 (Actin-like protein Arp8) is a unique subunit within the chromatin remodeling complex INO80, regulating processes including chromatin remodeling. However, the biological function of Arp8 in A. flavus remains unclear. This study constructed A. flavus arp8 knockout (Δarp8) and complementation (Com-arp8) strains via homologous recombination. Subsequent research revealed that following the deletion of arp8, A. flavus exhibits a reduction of approximately 51% in conidia production, complete abrogation of sclerotia formation, and significantly impairment of aflatoxin B1 (AFB1) biosynthesis. Crop grain colonization and Bombyx mori Linnaeus, 1758 infection models demonstrated that Arp8 plays a crucial role in A. flavus ability to infect hosts. Environmental stress experiments identified Arp8 as a vital factor for A. flavus in response to various environmental stresses. Quantitative RT-PCR (qRT-PCR) analysis indicated Arp8 achieves its biological functions through corresponding regulatory factors. This study elucidates the biological functions of Arp8 in A. flavus growth and development, pathogenicity, and aflatoxin synthesis, laying a foundation to illuminate the mechanisms of A. flavus pathogenicity and AFs production.

Aspergillus flavus, a ubiquitous phytopathogen, produces mycotoxins, especially aflatoxin B₁ (AFB₁), and infects crops worldwide. Glycerol-3-phosphate dehydrogenase (G3PDH) is a key enzyme in the glycerol synthesis and metabolic pathway catalyzing the reversible conversion reaction between glycerol-3-phosphate (G3P) and dihydroxyacetone phosphate (DHAP). However, the biological function of G3PDH in A. flavus remains uncharacterized. In this study, the glycerol-3-phosphate dehydrogenase GfdA and GfdB recombinant proteins of A. flavus were expressed, and the enzymatic activity of the GfdA protein was successfully determined. Subsequently, single-gene knockout strains (ΔgfdA, ΔgfdB), double-gene knockout strains (ΔgfdAΔgfdB) and their corresponding complemented strains (gfdA^C, gfdB^C) were constructed by a homologous recombination method to explore the biological functions of these two genes in A. flavus. The phenotypic analyses revealed that although both gfdA and gfdB encoded glycerol-3-phosphate dehydrogenases, gfdA plays major roles in colony growth, conidiation, sclerotium formation, crop infection and osmotic stress tolerance in A. flavus. Notably, the performance of the ΔgfdAΔgfdB strains is almost similar to that of the ΔgfdA strain. Biochemical assays demonstrated that the intracellular glycerol content increased significantly in all mutants compared to the wild type (WT) under both normal and osmotic stress conditions. Furthermore, we found that exogenous glycerol supplementation rescued the growth defect of the ΔgfdA and ΔgfdAΔgfdB strains. Taken together, GfdA is important for glycerol synthesis, while GfdB is functionally redundant with respect to GfdA. This study preliminarily explores the main biological functions of GfdA and GfdB, providing a theoretical basis for the study of glycerol anabolic pathways of A. flavus and also offering novel insights into the development of strategies to control aflatoxin contamination.