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Aspergillus flavus, a fungus known for producing aflatoxins, poses significant threats to agriculture and global health. Flavonoids, plant-derived compounds, inhibit A. flavus proliferation and mitigate aflatoxin production, although the precise molecular and physical mechanisms underlying these effects remain poorly understood. In this study, we investigated three flavonoids—apigenin, luteolin, and quercetin—applied to A. flavus NRRL 3357. We determined the following: (1) glycosylated luteolin led to a 10% reduction in maximum fungal growth capacity; (2) quercetin affected cell wall integrity by triggering extreme mycelial collapse, while apigenin and luteolin caused peeling of the outer layer of cell wall; (3) luteolin exhibited the highest antioxidant capacity in the environment compared to apigenin and quercetin; (4) osmotic stress assays did not reveal morphological defects; (5) flavonoids promoted cell adherence, a precursor for biofilm formation; and (6) RNA sequencing analysis revealed that flavonoids impact expression of putative cell wall and plasma membrane biosynthesis genes. Our findings suggest that the differential effects of quercetin, luteolin, and apigenin on membrane integrity and biofilm formation may be driven by their interactions with fungal cell walls. These insights may inform the development of novel antifungal additives or plant breeding strategies focusing on plant-derived compounds in crop protection. [ABSTRACT FROM AUTHOR]

Aspergillus flavus is an agriculturally significant micro‐fungus having potential to contaminate food and feed crops with toxic secondary metabolites such as aflatoxin (AF) and cyclopiazonic acid (CPA). Research has shown A. flavus strains can overcome heterokaryon incompatibility and undergo meiotic recombination as teleomorphs. Although evidence of recombination in the AF gene cluster has been reported, the impacts of recombination on genotype and metabolomic phenotype in a single generation are lacking. In previous studies, we paired an aflatoxigenic MAT1‐1 A. flavus strain with a non‐aflatoxigenic MAT1‐2 A. flavus strain that had been tagged with green fluorescent protein and then 10 F1 progenies (a mix of fluorescent and non‐fluorescent) were randomly selected from single‐ascospore colonies and broadly examined for evidence of recombination. In this study, we determined four of those 10 F1 progenies were recombinants because they were not vegetatively compatible with either parent or their siblings, and they exhibited other distinctive traits that could only result from meiotic recombination. The other six progenies examined shared genomic identity with the non‐aflatoxigenic, fluorescent, and MAT1‐2 parent, but were metabolically distinct. This study highlights phenotypic and genomic changes that may occur in a single generation from the outcrossing of sexually compatible strains of A. flavus. [ABSTRACT FROM AUTHOR]

Aspergillus flavus is a saprophytic fungus that may colonize several important crops, including cotton, maize, peanuts and tree nuts. Concomitant with A. flavus colonization is its potential to secrete mycotoxins, of which the most prominent is aflatoxin. Temperature, water activity (aw) and carbon dioxide (CO2) are three environmental factors shown to influence the fungus-plant interaction, which are predicted to undergo significant changes in the next century. In this study, we used RNA sequencing to better understand the transcriptomic response of the fungus to aw, temperature, and elevated CO2 levels. We demonstrate that aflatoxin (AFB1) production on maize grain was altered by water availability, temperature and CO2. RNA-Sequencing data indicated that several genes, and in particular those involved in the biosynthesis of secondary metabolites, exhibit different responses to water availability or temperature stress depending on the atmospheric CO2 content. Other gene categories affected by CO2 levels alone (350 ppm vs. 1000 ppm at 30 °C/0.99 aw), included amino acid metabolism and folate biosynthesis. Finally, we identified two gene networks significantly influenced by changes in CO2 levels that contain several genes related to cellular replication and transcription. These results demonstrate that changes in atmospheric CO2 under climate change scenarios greatly influences the response of A. flavus to water and temperature when colonizing maize grain. [ABSTRACT FROM AUTHOR]

Homeobox proteins, a class of well conserved transcription factors, regulate the expression of targeted genes, especially those involved in development. In filamentous fungi, homeobox genes are required for normal conidiogenesis and fruiting body formation. In the present study, we identified eight homeobox (hbx) genes in the aflatoxin-producing ascomycete, Aspergillus flavus, and determined their respective role in growth, conidiation and sclerotial production. Disruption of seven of the eight genes had little to no effect on fungal growth and development. However, disruption of the homeobox gene AFLA_069100, designated as hbx1, in two morphologically different A. flavus strains, CA14 and AF70, resulted in complete loss of production of conidia and sclerotia as well as aflatoxins B1 and B2, cyclopiazonic acid and aflatrem. Microscopic examination showed that the Δhbx1 mutants did not produce conidiophores. The inability of Δhbx1 mutants to produce conidia was related to downregulation of brlA (bristle) and abaA (abacus), regulatory genes for conidiophore development. These mutants also had significant downregulation of the aflatoxin pathway biosynthetic genes aflC, aflD, aflM and the cluster-specific regulatory gene, aflR. Our results demonstrate that hbx1 not only plays a significant role in controlling A. flavus development but is also critical for the production of secondary metabolites, such as aflatoxins. [ABSTRACT FROM AUTHOR]

Aspergillus bombycis was first isolated from silkworm frass in Japan. It has been reportedly misidentified as A. nomius due to their macro-morphological and chemotype similarities. We sequenced the genome of the A. bombycis Type strain and found it to be comparable in size (37Mb), as well as in numbers of predicted genes (12,266), to other sequenced Aspergilli. The aflatoxin gene cluster in this strain is similar in size and the genes are oriented the same as other B- + G-aflatoxin producing species, and this strain contains a complete but nonfunctional gene cluster for the production of cyclopiazonic acid. Our findings also showed that the A. bombycis Type strain contains a single MAT1-2 gene indicating that this species is likely heterothallic (self-infertile). This draft genome will contribute to our understanding of the genes and pathways necessary for aflatoxin synthesis as well as the evolutionary relationships of aflatoxigenic fungi. [ABSTRACT FROM AUTHOR]

Aspergillus ochraceoroseus and Aspergillus rambellii were isolated from soil detritus in Taï National Park, Ivory Coast, Africa. The Type strain for each species happens to be the only representative ever sampled. Both species secrete copious amounts of aflatoxin B1 and sterigmatocystin, because each of their genomes contains clustered genes for biosynthesis of the semycotoxins. We sequenced their genomes using a personal genome machine and found them to be smaller in size (A. ochraceoroseus = 23.9Mb and A. rambellii = 26.1 Mb), as well as in numbers of predicted genes (7,837 and 7,807, respectively), compared to other sequenced Aspergilli. Our findings also showed that the A. ochraceoroseus Type strain contains a single MAT1-1 gene, while the Type strain of A. rambellii contains a single MAT1-2 gene, indicating that these species are heterothallic (self-infertile). These draft genomes will be useful for understanding the genes and pathways necessary for the cosynthesis of these two toxic secondary metabolites as well as the evolution of these pathways in aflatoxigenic fungi. [ABSTRACT FROM AUTHOR]

Fifty six secondary metabolite biosynthesis gene clusters are predicted to be in the Aspergillus flavus genome. In spite of this, the biosyntheses of only seven metabolites, including the aflatoxins, kojic acid, cyclopiazonic acid and aflatrem, have been assigned to a particular gene cluster. We used RNA-seq to compare expression of secondary metabolite genes in gene clusters for the closely related fungi A. parasiticus, A. oryzae, and A. flavus S and L sclerotial morphotypes. The data help to refine the identification of probable functional gene clusters within these species. Our results suggest that A. flavus, a prevalent contaminant of maize, cottonseed, peanuts and tree nuts, is capable of producing metabolites which, besides aflatoxin, could be an underappreciated contributor to its toxicity. [ABSTRACT FROM AUTHOR]

Aflatoxins are the most potent naturally occurring carcinogens of fungal origin. Biosynthesis of aflatoxin involves the coordinated expression of more than 25 genes. The function of one gene in the aflatoxin gene cluster, aflJ, is not entirely understood but, because previous studies demonstrated a physical interaction between the Zn2Cys6 transcription factor AflR and AflJ, AflJ was proposed to act as a transcriptional co-activator. Image analysis revealed that, in the absence of aflJ in A. parasiticus, endosomes cluster within cells and near septa. AflJ fused to yellow fluorescent protein complemented the mutation in A. parasiticus Δ?aflJ and localized mainly in endosomes. We found that AflJ co-localizes with AflR both in endosomes and in nuclei. Chromatin immunoprecipitation did not detect AflJ binding at known AflR DNA recognition sites suggesting that AflJ either does not bind to these sites or binds to them transiently. Based on these data, we hypothesize that AflJ assists in AflR transport to or from the nucleus, thus controlling the availability of AflR for transcriptional activation of aflatoxin biosynthesis cluster genes. AflJ may also assist in directing endosomes to the cytoplasmic membrane for aflatoxin export. [ABSTRACT FROM AUTHOR]

Aflatoxin is a carcinogenic mycotoxin produced by Aspergillus flavus. Non-aflatoxigenic (Non-tox) A. flavus isolates are deployed in corn fields as biocontrol because they substantially reduce aflatoxin contamination via direct replacement and additionally via direct contact or touch with toxigenic (Tox) isolates and secretion of inhibitory/degradative chemicals. To understand touch inhibition, HPLC analysis and RNA sequencing examined aflatoxin production and gene expression of Non-tox isolate 17 and Tox isolate 53 mono-cultures and during their interaction in co-culture. Aflatoxin production was reduced by 99.7% in 72 h co-cultures. Fewer than expected unique reads were assigned to Tox 53 during co-culture, indicating its growth and/or gene expression was inhibited in response to Non-tox 17. Predicted secreted proteins and genes involved in oxidation/reduction were enriched in Non-tox 17 and co-cultures compared to Tox 53. Five secondary metabolite (SM) gene clusters and kojic acid synthesis genes were upregulated in Non-tox 17 compared to Tox 53 and a few were further upregulated in co-cultures in response to touch. These results suggest Non-tox strains can inhibit growth and aflatoxin gene cluster expression in Tox strains through touch. Additionally, upregulation of other SM genes and redox genes during the biocontrol interaction demonstrates a potential role of inhibitory SMs and antioxidants as additional biocontrol mechanisms and deserves further exploration to improve biocontrol formulations. [ABSTRACT FROM AUTHOR]

Background: Aspergillus arachidicola is an aflatoxigenic fungal species, first isolated from the leaves of a wild peanut species native to Argentina. It has since been reported in maize, Brazil nut and human sputum samples. This aflatoxigenic species is capable of secreting both B and G aflatoxins, similar to A. parasiticus and A. nomius. It has other characteristics that may result in its misidentification as one of several other section Flavi species. This study offers a preliminary analysis of the A. arachidicola genome. Results: In this study we sequenced the genome of the A. arachidicola type strain (CBS 117610) and found its genome size to be 38.9 Mb, and its number of predicted genes to be 12,091, which are values comparable to those in other sequenced Aspergilli. A comparison of 57 known Aspergillus secondary metabolite gene clusters, among closely-related aflatoxigenic species, revealed nearly half were predicted to exist in the type strain of A. arachidicola. Of its predicted genes, 691 were identified as unique to the species and 60% were assigned Gene Ontology terms using BLAST2GO. Phylogenomic inference shows CBS 117610 sharing a most recent common ancestor with A. parasiticus. Finally, BLAST query of A. flavus mating-type idiomorph sequences to this strain revealed the presence of a single mating-type (MAT1–1) idiomorph. Conclusions: Based on A. arachidicola morphological, genetic and chemotype similarities with A. flavus and A. parasiticus, sequencing the genome of A. arachidicola will contribute to our understanding of the evolutionary relatedness among aflatoxigenic fungi. [ABSTRACT FROM AUTHOR]