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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Food and Feed Safety Research » Research » Publications at this Location » Publication #337994

Research Project: Genetic and Environmental Factors Controlling Aflatoxin Biosynthesis

Location: Food and Feed Safety Research

Title: Aspergillus flavus aswA, a gene homolog of Aspergillus nidulans oefC, regulates sclerotial development and biosynthesis of sclerotium-associated secondary metabolites

Author
item Chang, Perng Kuang
item Scharfenstein, Leslie - Les
item Li, Robert
item Arroyo-manzanares, Natalia - Ghent University
item De Saeger, Sarah - Ghent University
item Diana Di Mavungu, Jose - Ghent University

Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/21/2017
Publication Date: 4/22/2017
Citation: Chang, P.-K., Scharfenstein, L.L., Li, R.W., Arroyo-Manzanares, N., De Saeger, S., Diana Di Mavungu, J. 2017. Aspergillus flavus aswA, a gene homolog of Aspergillus nidulans oefC, regulates sclerotial development and biosynthesis of sclerotium-associated secondary metabolites. Fungal Genetics and Biology. 104:29-37.

Interpretive Summary: Aspergillus flavus infects crops and produces carcinogenic aflatoxin B1. It is also an opportunistic pathogen of animals and humans. Conidia and sclerotia are two main types of propagules during its asexual life cycle. Sclerotia are a resting body consisting of hardened hyphal threads and able to remain dormant for long periods. Few genes directly involved in sclerotial development have been reported in A. flavus. In this work, we identified a regulatory gene that controlled sclerotial maturation including proper shape formation. This gene also regulated accumulation of several tremogenic compounds in mature sclerotia. Collectively, our findings suggest that sclerotial development and production of sclerotium-specific metabolites are co-regulated. The potent antifeedant activity of the metabolites in the mature sclerotia functions to enhance fungal survival.

Technical Abstract: Aspergillus flavus aswA (AFLA_085170) is a gene encoding a Zn(II)2Cys6 DNA-binding domain. Partial deletion of aswA yielded strains that made a truncated gene transcript and generated a fungus that produced a greatly increased number of sclerotia. These sclerotia were odd-shaped and non-pigmented (white) and different from oval and pigmented (dark brown to black) mature sclerotia. Transcriptomic analysis of the 'aswA strain grown on potato dextrose agar plates and Wickerham agar plates showed that expression of clustering genes involved in the biosynthesis of three sclerotium-associated secondary metabolites was down-regulated. These included gene clusters of asparasone, aflatrem, and aflavarin. In contrast, those of aflatoxin, cyclopiazonic acid and kojic acid were not affected. Metabolite analyses confirmed that the non-pigmented sclerotia contained aflatoxin and cyclopiazonic acid but not other aforementioned metabolites, three asparasone analogs and dihydroxyaflavinine commonly present in mature sclerotia. Impairment in aswA gene function stalls normal sclerotial development, which in turn prevents biosynthesis and accumulation of sclerotium-specific metabolites.