Section Flavi encompasses both harmful and beneficial Aspergillus species, such as Aspergillus oryzae, used in food fermentation and enzyme production, and Aspergillus flavus, food spoiler and ...mycotoxin producer. Here, we sequence 19 genomes spanning section Flavi and compare 31 fungal genomes including 23 Flavi species. We reassess their phylogenetic relationships and show that the closest relative of A. oryzae is not A. flavus, but A. minisclerotigenes or A. aflatoxiformans and identify high genome diversity, especially in sub-telomeric regions. We predict abundant CAZymes (598 per species) and prolific secondary metabolite gene clusters (73 per species) in section Flavi. However, the observed phenotypes (growth characteristics, polysaccharide degradation) do not necessarily correlate with inferences made from the predicted CAZyme content. Our work, including genomic analyses, phenotypic assays, and identification of secondary metabolites, highlights the genetic and metabolic diversity within section Flavi.
Summary
Mitogen‐activated protein kinase (MAPK) cascades are highly conserved in eukaryotic cells and are known to play crucial roles in the regulation of various cellular processes. However, ...compared with kinase‐mediated phosphorylation, dephosphorylation catalysed by phosphatases has not been well characterized in filamentous fungi. In this study, we identified five MAPK pathway‐related phosphatases (Msg5, Yvh1, Ptp1, Ptp2 and Oca2) and characterized their functions in Aspergillus flavus, which produces aflatoxin B1 (AFB1), one of the most toxic and carcinogenic secondary metabolites. These five phosphatases were identified as negative regulators of MAPK (Slt2, Fus3 and Hog1) pathways. Deletion of Msg5 and Yvh1 resulted in significant defects in conidiation, sclerotia formation, aflatoxin production and crop infection. Additionally, double knockout mutants (ΔMsg5/ΔPtp1, ΔMsg5/ΔPtp2 and ΔMsg5/ΔOca2) displayed similar defects to those observed in the ΔMsg5 single mutant, indicating that Msg5 plays a major role in the regulation of development and pathogenicity in A. flavus. Importantly, we found that the active site at C439 is essential for the function of the Msg5 phosphatase. Furthermore, the MAP kinase Fus3 was found to be involved in the regulation of development, aflatoxin biosynthesis and pathogenicity, and its conserved phosphorylation residues (Thr and Tyr) were critical for the full range of its functions in A. flavus. Overall, our results reveal that MAPK related tyrosine phosphatases play important roles in the regulation of development, secondary metabolism and pathogenicity in A. flavus, and could be developed as potential targets for preventing damage caused by this fungal pathogen.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Velvet (VeA), a light-regulated protein that shuttles between the cytoplasm and the nucleus, serves as a key global regulator of secondary metabolism in various
species and plays a pivotal role in ...controlling multiple developmental processes. The gene
was chosen for further investigation through CHIP-seq analysis due to significant alterations in its interaction with VeA under varying conditions. This gene (AFLA_006970) contains a Septin-type guanine nucleotide-binding (G) domain, which has not been previously reported in
(
). The functional role of
in
was elucidated through the creation of a gene knockout mutant and a gene overexpression strain using a well-established dual-crossover recombinational technique. A comparison between the wild type (WT) and the Δ
mutant revealed distinct differences in morphology, reproductive capacity, colonization efficiency, and aflatoxin production. The mutant displayed reduced growth rate; dispersion of conidial heads; impaired cell wall integrity; and decreased sclerotia formation, colonization capacity, and aflatoxin levels. Notably, Δ
exhibited complete growth inhibition under specific stress conditions, highlighting the essential role of
in
. This study provides evidence that
positively influences aflatoxin production, morphological development, and pathogenicity in
.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•SntB has a conserved pleiotropic response to genetic manipulation in filamentous fungi.•SntB regulates sclerotia and heterokaryon formation, likely through transcriptional regulation of ...nosA.•Epigenetic reading proteins can be master regulators of secondary metabolism.•SntB regulates global levels of histone H3 acetylation.
Due to the role, both beneficial and harmful, that fungal secondary metabolites play in society, the study of their regulation is of great importance. Genes for any one secondary metabolite are contiguously arranged in a biosynthetic gene cluster (BGC) and subject to regulation through the remodeling of chromatin. Histone modifying enzymes can place or remove post translational modifications (PTM) on histone tails which influences how tight or relaxed the chromatin is, impacting transcription of BGCs. In a recent forward genetic screen, the epigenetic reader SntB was identified as a transcriptional regulator of the sterigmatocystin BGC in A. nidulans, and regulated the related metabolite aflatoxin in A. flavus. In this study we investigate the role of SntB in the plant pathogen A. flavus by analyzing both ΔsntB and overexpression sntB genetic mutants. Deletion of sntB increased global levels of H3K9K14 acetylation and impaired several developmental processes including sclerotia formation, heterokaryon compatibility, secondary metabolite synthesis, and ability to colonize host seeds; in contrast the overexpression strain displayed fewer phenotypes. ΔsntB developmental phenotypes were linked with SntB regulation of NosA, a transcription factor regulating the A. flavus cell fusion cascade.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Hexavalent chromium reduction by microbes can mitigate the chromium toxicity to the environment. In the present study CrVI tolerant fungal isolate (CR500) was isolated from electroplating wastewater, ...was able to tolerate 800 mg/L of CrVI. Based on the ITS region sequencing, the isolate was identified as Aspergillus flavus CR500, showed multifarious biochemical (reactive oxygen species, antioxidants response and non-protein thiol) and morphological (protrusion less, constriction and swelling/outwards growth in mycelia) response under CrVI stress. Batch experiment was conducted at different CrVI concentration (0–200 mg/L) to optimize the CrVI reduction and removal ability of isolate CR500; results showed 89.1% reduction of CrVI to CrIII within 24 h and 4.9 ± 0.12 mg of Cr per gram of dried biomass accumulation within 144 h at the concentration of 50 mg/L of CrVI. However, a maximum of 79.4% removal of Cr was recorded at 5 mg/L within 144 h. Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy and X-ray diffraction analysis revealed that chromium removal also happened via adsorption/precipitation on the mycelia surface. Fungus treated and without treated 100 mg/L of CrVI solution was subjected to phytotoxicity test using Vigna radiata seeds and result revealed that A. flavus CR500 successfully detoxified the CrVI via reduction and removal mechanisms. Isolate CR500 also exhibited efficient bioreduction potential at different temperature (20–40 °C), pH (5.0–9.0), heavy metals (As, Cd, Cu, Mn, Ni and Pb), metabolic inhibitors (phenol and EDTA) and in sterilized tannery effluent that make it a potential candidate for CrVI bioremediation.
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•A. flavus CR500 show multifarious biochemical and morphological response to deals with CrVI toxicity.•CrVI induced chromate reductase play a major role in the reduction of CrVI to CrIII.•Accumulation, precipitation and adsorption mechanism involve in Cr removal by isolate CR500.•Isolate CR500 has excellent CrVI bioremediation potential.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
is an opportunistic fungal plant and human pathogen and a producer of mycotoxins, including aflatoxin B
(AFB
). As part of our ongoing studies to elucidate the biological functions of the
gene, we ...examined its role in the pathogenicity of both plant and animal model systems.
encodes a putative RNA polymerase II (Pol II) transcription elongation factor previously characterized in
,
, and
, where it was shown to regulate several important cellular processes, including morphogenesis and secondary metabolism. In addition, an initial study in
indicated that
also influences development and production of AFB
; however, its effect on virulence is unknown. The current study reveals that the
gene is indispensable for normal pathogenicity in plants when using peanut seed as an infection model, as well as in animals, as shown in the
infection model. Interestingly,
positively regulates several processes known to be necessary for successful fungal invasion and colonization of host tissue, such as adhesion to surfaces, protease and lipase activity, cell wall composition and integrity, and tolerance to oxidative stress. In addition, metabolomic analysis revealed that
affects the production of several secondary metabolites, including AFB
, aflatrem, leporins, aspirochlorine, ditryptophenaline, and aflavinines, supporting a role of
as a global regulator of secondary metabolism. Heterologous complementation of an
deletion strain with
homologs from
or
fully rescued the wild-type phenotype, indicating that these
homologs are functionally conserved among these three species.
In this study, the epigenetic global regulator
, which encodes a putative RNA-Pol II transcription elongation factor-like protein, was characterized in the mycotoxigenic and opportunistic pathogen
Specifically, its involvement in
pathogenesis in plant and animal models was studied. Here, we show that
positively regulates
virulence in both models. Furthermore,
-dependent effects on factors necessary for successful invasion and colonization of host tissue by
were also assessed. Our study indicates that
plays a role in
adherence to surfaces, hydrolytic activity, normal cell wall formation, and response to oxidative stress. This study also revealed a profound effect of
on the metabolome of
, including the production of potent mycotoxins.
Spices are used extensively in Lebanon not only to flavour foods but also for their medicinal properties. To date, no data are available regarding the nature of the toxigenic fungal species that may ...contaminate these products at the marketing stage in this country. Eighty samples corresponding to 14 different types of spices were collected throughout Lebanon to characterize the Aspergillus section Flavi contaminating spices marketed in Lebanon and the toxigenic potential of these fungal species. Most fungal genera and species were identified as belonging to Aspergillus section Flavi. Aspergillus flavus was the most frequent species, representing almost 80% of the isolates. Although identified as A. flavus by molecular analysis, some strains displayed atypical morphological features. Seven strains of A. tamarii and one A. minisclerotigenes were also isolated. Analyses of toxigenic potential demonstrated that almost 80% of strains were able to produce mycotoxins, 47% produced aflatoxins, and 72% produced cyclopiazonic acid, alone or in combination with aflatoxins.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Summary
Maize infected by aflatoxin‐producing Aspergillus flavus may become contaminated with aflatoxins, and as a result, threaten human health, food security and farmers' income in developing ...countries where maize is a staple. Environmental distribution and genetic diversity of A. flavus can influence the effectiveness of atoxigenic isolates in mitigating aflatoxin contamination. However, such information has not been used to facilitate selection and deployment of atoxigenic isolates. A total of 35 isolates of A. flavus isolated from maize samples collected from three agro‐ecological zones of Nigeria were used in this study. Ecophysiological characteristics, distribution and genetic diversity of the isolates were determined to identify vegetative compatibility groups (VCGs). The generated data were used to inform selection and deployment of native atoxigenic isolates to mitigate aflatoxin contamination in maize. In co‐inoculation with toxigenic isolates, atoxigenic isolates reduced aflatoxin contamination in grain by > 96%. A total of 25 VCGs were inferred from the collected isolates based on complementation tests involving nitrate non‐utilizing (nit−) mutants. To determine genetic diversity and distribution of VCGs across agro‐ecological zones, 832 nit− mutants from 52 locations in 11 administrative districts were paired with one self‐complementary nitrate auxotroph tester‐pair for each VCG. Atoxigenic VCGs accounted for 81.1% of the 153 positive complementations recorded. Genetic diversity of VCGs was highest in the derived savannah agro‐ecological zone (H = 2.61) compared with the southern Guinea savannah (H = 1.90) and northern Guinea savannah (H = 0.94) zones. Genetic richness (H = 2.60) and evenness (E5 = 0.96) of VCGs were high across all agro‐ecological zones. Ten VCGs (40%) had members restricted to the original location of isolation, whereas 15 VCGs (60%) had members located between the original source of isolation and a distance > 400 km away. The present study identified widely distributed VCGs in Nigeria such as AV0222, AV3279, AV3304 and AV16127, whose atoxigenic members can be deployed for a region‐wide biocontrol of toxigenic isolates to reduce aflatoxin contamination in maize.
Environmental distribution and genetic diversity of A. flavus can influence the effectiveness of atoxigenic isolates in mitigating aflatoxin contamination. A total of 35 isolates of A. flavus isolated from maize samples collected from three agroecological zones of Nigeria were used in this study and ecophysiological characteristics, distribution, and genetic diversity of the isolates were determined to identify vegetative compatibility groups (VCGs). Genetic diversity of VCGs was highest in the Derived Savanna agroecological zone (H = 2.61) compared to the Southern Guinea Savanna (H = 1.90) and Northern Guinea Savanna (H = 0.94) zones. The present study identified widely distributed VCGs in Nigeria such as AV0222, AV3279, AV3304, and AV16127, whose atoxigenic members can be deployed for a region‐wide biocontrol of toxigenic isolates to reduce aflatoxin contamination in maize.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Aflatoxin biosynthesis is correlated with oxidative stress and is proposed to function as a secondary defense mechanism to redundant intracellular reactive oxygen species (ROS). We find that the ...antioxidant gallic acid inhibits aflatoxin formation and growth in
in a dose-dependent manner. Global expression analysis (RNA-Seq) of gallic acid-treated
showed that 0.8% (
/
) gallic acid revealed two possible routes of aflatoxin inhibition. Gallic acid significantly inhibited the expression of
, encoding a transcription factor that participates in peroxisomal fatty acid β-oxidation, a fundamental contributor to aflatoxin production. Secondly, the carbon repression regulator encoding gene,
, was significantly down regulated by gallic acid treatment. CreA is necessary for aflatoxin synthesis, and aflatoxin biosynthesis genes were significantly downregulated in ∆
mutants. In addition, the results of antioxidant enzyme activities and the lipid oxidation levels coupled with RNA-Seq data of antioxidant genes indicated that gallic acid may reduce oxidative stress through the glutathione- and thioredoxin-dependent systems in
.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Aspergillus flavus is a saprophytic fungus and pathogen to several important food and feed crops, including maize. Once the fungus colonizes lipid-rich seed tissues, it has the potential to produce ...toxic secondary metabolites, the most dangerous of which is aflatoxin. The pre-harvest control of A. flavus contamination and aflatoxin production is an area of intense research, which includes breeding strategies, biological control, and the use of genetically-modified crops. Host-induced gene silencing, whereby the host crop produces siRNA molecules targeting crucial genes in the invading fungus and targeting the gene for degradation, has shown to be promising in its ability to inhibit fungal growth and decrease aflatoxin contamination. Here, we demonstrate that maize inbred B104 expressing an RNAi construct targeting the A. flavus alpha-amylase gene amy1 effectively reduces amy1 gene expression resulting in decreased fungal colonization and aflatoxin accumulation in kernels. This work contributes to the development of a promising technology for reducing the negative economic and health impacts of A. flavus growth and aflatoxin contamination in food and feed crops.
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