Genetic and Molecular Analysis of Aflatoxin Biosynthesis

Brown, Martin; Brown-Jenco, C.S.; Payne, Gary A.

doi:10.1006/fgbi.1998.1114

Cited by 65 publications

(31 citation statements)

References 118 publications

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“…During the biosynthesis of these secondary metabolites, many biosynthetic enzymes are required and should function coordinately in the synthesis of these structurally complex metabolites. The genes encoding these enzymes have often been reported to localize in an adjacent region or to form a gene cluster (6,13), similar to the situation of biosynthetic gene clusters for secondary metabolites in prokaryotic actinomycetes. In addition to such structural genes, each gene cluster may contain a gene encoding a regulator that functions to coordinate expression of the structural genes in the cluster and a gene encoding a transporter that excludes harmful intracellular secondary metabolites as a self-defense mechanism (7,22), respectively.…”

mentioning

confidence: 87%

Identification and In Vivo Functional Analysis by Gene Disruption of ctnA , an Activator Gene Involved in Citrinin Biosynthesis in Monascus purpureus

Shimizu

Kinoshita

Nihira

2007

Appl Environ Microbiol

109

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Citrinin, a secondary fungal metabolite of polyketide origin, is moderately nephrotoxic to vertebrates, including humans. From the red-pigment producer Monascus purpureus, a 21-kbp region flanking pksCT, which encodes citrinin polyketide synthase, was cloned. Four open reading frames (ORFs) (orf1, orf2, orf3, and orf4) in the 5-flanking region and one ORF (orf5) in the 3-flanking region were identified in the vicinity of pksCT. orf1 to orf5 encode a homolog of a dehydrogenase (similarity, 46%), a regulator (similarity, 38%), an oxygenase (similarity, 41%), an oxidoreductase (similarity, 26%), and a transporter (similarity, 58%), respectively. orf2 (2,006 bp with four introns) encodes a 576-amino-acid protein containing a typical Zn(II)2Cys6 DNA binding motif at the N terminus and was designated ctnA. Although reverse transcriptase PCR analysis revealed that all of these ORFs, except for orf1, were transcribed with pksCT under citrinin production conditions, the disruption of ctnA caused large decreases in the transcription of pksCT and orf5, together with reduction of citrinin production to barely detectable levels, suggesting that these two genes are under control of the ctnA product. Complementation of the ctnA disruptant with intact ctnA on an autonomously replicating plasmid restored both transcription and citrinin production, indicating that CtnA is a major activator of citrinin biosynthesis.Filamentous fungi have a versatile ability to produce different kinds of secondary metabolites, including antibiotics, anticancer drugs, and pigments (3). During the biosynthesis of these secondary metabolites, many biosynthetic enzymes are required and should function coordinately in the synthesis of these structurally complex metabolites. The genes encoding these enzymes have often been reported to localize in an adjacent region or to form a gene cluster (6, 13), similar to the situation of biosynthetic gene clusters for secondary metabolites in prokaryotic actinomycetes. In addition to such structural genes, each gene cluster may contain a gene encoding a regulator that functions to coordinate expression of the structural genes in the cluster and a gene encoding a transporter that excludes harmful intracellular secondary metabolites as a self-defense mechanism (7, 22), respectively.Regulators possessing a Zn(II)2Cys6 binuclear motif represent one of the largest classes of transcriptional regulators in filamentous fungi. They generally act as transcriptional activators, as exemplified by GAL4 from Saccharomyces cerevisiae (21). A large number of Zn(II)2Cys6 regulators have been identified exclusively in fungi and characterized as regulators of primary metabolism, secondary metabolism, drug resistance, or meiotic development. Through its DNA binding motif (CX 2 CX 6 CX 6 CX 2 CX 6 C [C, cysteinyl residue; X, any amino acid]) located at the N terminus, the Zn(II)2Cys6 regulator binds to a specific binding site (CGGN 6/11 CCG [N, any nucleotide]) in the promoter regions of target genes. Previous research on secondary met...

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confidence: 87%

Identification and In Vivo Functional Analysis by Gene Disruption of ctnA , an Activator Gene Involved in Citrinin Biosynthesis in Monascus purpureus

Shimizu

Kinoshita

Nihira

2007

Appl Environ Microbiol

109

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“…The gene isolated, eln2, is constitutively expressed independently of fruiting and was found to encode a cytochrome P450, with 31% (220,473,529,530). Aflatoxin has recently been connected to the development of sclerotia and conidiospores in Aspergillus; when aflatoxin production is missing, development is blocked, and when aflatoxin is overexpressed, development is increased (49,152,473,474). It is therefore likely that aflatoxin plays a biological role in development and that one possible function would be in signaling.…”

Section: Mutant Analysismentioning

confidence: 99%

Life History and Developmental Processes in the BasidiomyceteCoprinus cinereus

Kües

2000

Microbiol Mol Biol Rev

435

336

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SUMMARY Coprinus cinereus has two main types of mycelia, the asexual monokaryon and the sexual dikaryon, formed by fusion of compatible monokaryons. Syngamy (plasmogamy) and karyogamy are spatially and temporally separated, which is typical for basidiomycetous fungi. This property of the dikaryon enables an easy exchange of nuclear partners in further dikaryotic-monokaryotic and dikaryotic-dikaryotic mycelial fusions. Fruiting bodies normally develop on the dikaryon, and the cytological process of fruiting-body development has been described in its principles. Within the specialized basidia, present within the gills of the fruiting bodies, karyogamy occurs in a synchronized manner. It is directly followed by meiosis and by the production of the meiotic basidiospores. The synchrony of karyogamy and meiosis has made the fungus a classical object to study meiotic cytology and recombination. Several genes involved in these processes have been identified. Both monokaryons and dikaryons can form multicellular resting bodies (sclerotia) and different types of mitotic spores, the small uninucleate aerial oidia, and, within submerged mycelium, the large thick-walled chlamydospores. The decision about whether a structure will be formed is made on the basis of environmental signals (light, temperature, humidity, and nutrients). Of the intrinsic factors that control development, the products of the two mating type loci are most important. Mutant complementation and PCR approaches identified further genes which possibly link the two mating-type pathways with each other and with nutritional regulation, for example with the cAMP signaling pathway. Among genes specifically expressed within the fruiting body are those for two galectins, β-galactoside binding lectins that probably act in hyphal aggregation. These genes serve as molecular markers to study development in wild-type and mutant strains. The isolation of genes for potential non-DNA methyltransferases, needed for tissue formation within the fruiting body, promises the discovery of new signaling pathways, possibly involving secondary fungal metabolites.

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“…A wealth of knowledge has accumulated on the aflatoxin biosynthetic pathways (6,11). The genes are clustered, with approximately 25 genes within a 60-to 70-kb region of the genome, although the order of homologous genes differs between the aflatoxin cluster of A. parasiticus (53) and the sterigmatocystin cluster of A. nidulans (10,14).…”

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confidence: 99%

Dothistroma pini , a Forest Pathogen, Contains Homologs of Aflatoxin Biosynthetic Pathway Genes

Bradshaw

Bhatnagar

Ganley

et al. 2002

Appl Environ Microbiol

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Homologs of aflatoxin biosynthetic genes have been identified in the pine needle pathogen Dothistroma pini. D. pini produces dothistromin, a difuranoanthraquinone toxin with structural similarity to the aflatoxin precursor versicolorin B. Previous studies with purified dothistromin suggest a possible role for this toxin in pathogenicity. By using an aflatoxin gene as a hybridization probe, a genomic D. pini clone was identified that contained four dot genes with similarity to genes in aflatoxin and sterigmatocystin gene clusters with predicted activities of a ketoreductase (dotA), oxidase (dotB), major facilitator superfamily transporter (dotC), and thioesterase (dotD). A D. pini dotA mutant was made by targeted gene replacement and shown to be severely impaired in dothistromin production, confirming that dotA is involved in dothistromin biosynthesis. Accumulation of versicolorin A (a precursor of aflatoxin) by the dotA mutant confirms that the dotA gene product is involved in an aflatoxin-like biosynthetic pathway. Since toxin genes have been found to be clustered in fungi in every case analyzed so far, it is speculated that the four dot genes may comprise part of a dothistromin biosynthetic gene cluster. A fifth gene, ddhA, is not a homolog of aflatoxin genes and could be at one end of the dothistromin cluster. These genes will allow comparative biochemical and genetic studies of the aflatoxin and dothistromin biosynthetic pathways and may also lead to new ways to control Dothistroma needle blight.

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Genetic and Molecular Analysis of Aflatoxin Biosynthesis

Cited by 65 publications

References 118 publications

Identification and In Vivo Functional Analysis by Gene Disruption of ctnA , an Activator Gene Involved in Citrinin Biosynthesis in Monascus purpureus

Identification and In Vivo Functional Analysis by Gene Disruption of ctnA , an Activator Gene Involved in Citrinin Biosynthesis in Monascus purpureus

Life History and Developmental Processes in the BasidiomyceteCoprinus cinereus

Dothistroma pini , a Forest Pathogen, Contains Homologs of Aflatoxin Biosynthetic Pathway Genes

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