Aflatoxin Biosynthesis: Regulation and Subcellular Localization

Linz, John E.; Wee, Josephine; Roze, Ludmila V.

doi:10.1007/978-1-4939-1191-2_5

Cited by 7 publications

(7 citation statements)

References 97 publications

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“…Triplicate cultures of SU-1, JW12, and JW13 were grown in YES liquid medium under standard conditions (30 °C with shaking at 150 rpm in the dark) and harvested at designated time points. Aflatoxin B 1 concentration (μg) in the medium was quantified by ELISA using anti-aflatoxin B 1 polyclonal antibodies (Sigma-Aldrich, St. Louis, MO, USA) and normalized to mycelial dry weight (g), as previously described [ 46 , 47 ]. Data were analyzed for statistical significance using the computing environment R (R Development Core Team, 2005) using one-way ANOVA and a post hoc Tukey’s test for pairwise comparisons.…”

Section: Methodsmentioning

confidence: 99%

The Fungal bZIP Transcription Factor AtfB Controls Virulence-Associated Processes in Aspergillus parasiticus

Wee

Hong

Roze

et al. 2017

Toxins

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Fungal basic leucine zipper (bZIP) transcription factors mediate responses to oxidative stress. The ability to regulate stress response pathways in Aspergillus spp. was postulated to be an important virulence-associated cellular process, because it helps establish infection in humans, plants, and animals. Previous studies have demonstrated that the fungal transcription factor AtfB encodes a protein that is associated with resistance to oxidative stress in asexual conidiospores, and AtfB binds to the promoters of several stress response genes. Here, we conducted a gene silencing of AtfB in Aspergillus parasiticus, a well-characterized fungal pathogen of plants, animals, and humans that produces the secondary metabolite and carcinogen aflatoxin, in order to determine the mechanisms by which AtfB contributes to virulence. We show that AtfB silencing results in a decrease in aflatoxin enzyme levels, the down-regulation of aflatoxin accumulation, and impaired conidiospore development in AtfB-silenced strains. This observation is supported by a decrease of AtfB protein levels, and the down-regulation of many genes in the aflatoxin cluster, as well as genes involved in secondary metabolism and conidiospore development. Global expression analysis (RNA Seq) demonstrated that AtfB functionally links oxidative stress response pathways to a broader and novel subset of target genes involved in cellular defense, as well as in actin and cytoskeleton arrangement/transport. Thus, AtfB regulates the genes involved in development, stress response, and secondary metabolism in A. parasiticus. We propose that the bZIP regulatory circuit controlled by AtfB provides a large number of excellent cellular targets to reduce fungal virulence. More importantly, understanding key players that are crucial to initiate the cellular response to oxidative stress will enable better control over its detrimental impacts on humans.

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Section: Methodsmentioning

confidence: 99%

The Fungal bZIP Transcription Factor AtfB Controls Virulence-Associated Processes in Aspergillus parasiticus

Wee

Hong

Roze

et al. 2017

Toxins

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“…Fluorescent antibodies toward aflatoxin and norsolorinic acid indicate accumulation of these compounds in discrete patches at the hyphal surface. These results have been explained by proposing that exocytosis of aflatoxisomes allows for export of both toxin and toxin biosynthetic enzymes (Chanda et al, 2010 ; Linz et al, 2014 ). The exact mechanism by which exocytosis may occur, whether by conventional exocytosis, Golgi-independent secretion, MVB-mediated secretion or by other non-canonical pathways (Shoji et al, 2014 ) is not known at this time.…”

Section: The Plasma Membrane and Beyond: Transporters Metabolite Tramentioning

confidence: 97%

“…Cytoplasm to vacuole transport may play a role in movement of cytoplasmic enzymes to the subcellular location where they are presumably active. Repositioning of Nor-1, Ver-1, and OmtA from the cytosol to vesicles is correlated with the timing of aflatoxin biosynthesis and protein modifications indicative of cytoplasm to vacuole transport (CVT) (Lee et al, 2004 ; Hong and Linz, 2008 , 2009 ; Roze et al, 2011 ; Linz et al, 2014 ). Aflatoxin biosynthetic enzyme Vbs is also thought to move from the cytoplasm to vesicles via the ER-Golgi secretory pathway during aflatoxin biosynthesis (Chiou et al, 2004 ).…”

Section: Cytosolmentioning

confidence: 99%

“…Mutants (avaA) and a chemical treatment (Sortin3) that disrupt fusion of late endosomes to vacuoles also increase the number of small vesicles, and increase aflatoxin levels in mycelium and in the culture medium (Chanda et al, 2009a ). Linz et al ( 2014 ) propose that two alternative pathways for aflatoxin traffic occur: one leading to the vacuole and resulting in the turnover of biosynthetic enzymes and reduced levels of the toxin and a second pathway mediated by the small mobile vesicles (termed “aflatoxisomes”), that contain the enzymes that synthesize aflatoxin and mediate its export (Figure 1B ). Inhibition of aflatoxisome traffic to the vacuole in avaA mutants or by Sortin3 therefore is proposed to increase the alternative pathway toward continued toxin synthesis and export.…”

Section: Vesicles Vesicle Traffic and Intracellular Transportmentioning

confidence: 99%

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Cellular compartmentalization of secondary metabolism

2015

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Fungal secondary metabolism is often considered apart from the essential housekeeping functions of the cell. However, there are clear links between fundamental cellular metabolism and the biochemical pathways leading to secondary metabolite synthesis. Besides utilizing key biochemical precursors shared with the most essential processes of the cell (e.g., amino acids, acetyl CoA, NADPH), enzymes for secondary metabolite synthesis are compartmentalized at conserved subcellular sites that position pathway enzymes to use these common biochemical precursors. Co-compartmentalization of secondary metabolism pathway enzymes also may function to channel precursors, promote pathway efficiency and sequester pathway intermediates and products from the rest of the cell. In this review we discuss the compartmentalization of three well-studied fungal secondary metabolite biosynthetic pathways for penicillin G, aflatoxin and deoxynivalenol, and summarize evidence used to infer subcellular localization. We also discuss how these metabolites potentially are trafficked within the cell and may be exported.

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“…vbs has been heterologous expressed, purified, isolated, and characterized in A. parasiticus (McGuire, Silva, Casillas, & Townsend, ; Silva, Minto, Barry, Holland, & Townsend, ; Silva & Townsend, ), and the distribution and subcellular localization of VBS was shown to change with respect to culture time in A. parasiticus (Chiou et al., ). Linz, Wee, & Roze () hypothesized that VBS transport is tightly regulated by the timing and synthesis level of versicolorin A.…”

Section: Introductionmentioning

confidence: 99%

Functional analyses of the versicolorin B synthase gene in Aspergillus flavus

et al. 2017

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Aflatoxin is a toxic, carcinogenic mycotoxin primarily produced by Aspergillus parasiticus and Aspergillus flavus. Previous studies have predicted the existence of more than 20 genes in the gene cluster involved in aflatoxin biosynthesis. Among these genes, aflK encodes versicolorin B synthase, which converts versiconal to versicolorin B. Past research has investigated aflK in A. parasiticus, but few studies have characterized aflK in the animal, plant, and human pathogen A. flavus. To understand the potential role of aflK in A. flavus, its function was investigated here for the first time using gene replacement and gene complementation strategies. The aflK deletion‐mutant ΔaflK exhibited a significant decrease in sclerotial production and aflatoxin biosynthesis compared with wild‐type and the complementation strain ΔaflK::aflK. ΔaflK did not affect the ability of A. flavus to infect seeds, but downregulated aflatoxin production after seed infection. This is the first report of a relationship between aflK and sclerotial production in A. flavus, and our findings indicate that aflK regulates aflatoxin formation.

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Aflatoxin Biosynthesis: Regulation and Subcellular Localization

Cited by 7 publications

References 97 publications

The Fungal bZIP Transcription Factor AtfB Controls Virulence-Associated Processes in Aspergillus parasiticus

The Fungal bZIP Transcription Factor AtfB Controls Virulence-Associated Processes in Aspergillus parasiticus

Cellular compartmentalization of secondary metabolism

Functional analyses of the versicolorin B synthase gene in Aspergillus flavus

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