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Abstract
Aflatoxins are carcinogenic secondary metabolites produced by the fungi Aspergillus flavus and Aspergillus parasiticus. Previous studies found that repeated serial mycelial transfer or treatment of A. parasiticus with 5-azacytidine produced colonies with a fluffy phenotype and inability to produce aflatoxins. To understand how these treatments affect expression of genes involved in aflatoxin production and development, we carried out expressed sequence tag (EST)-based microarray assays to identify genes in treated clones that are differentially expressed compared to the wild-type. Expression of 183 genes was significantly dysregulated. Of these, 38 had at least two-fold or lower expression compared to the untreated control and only two had two-fold or higher expression. The most frequent change was downregulation of genes predicted to encode membrane-bound proteins. Based on this result we hypothesize that the treatments cause changes in the structure of cellular and organelle membranes that prevent normal development and aflatoxin biosynthesis.
Highlights
Formation of the asexual reproductive structure called a conidiophore in Aspergillus species requires the concerted activity of a number of transcription factors and signaling proteins
G protein signaling and its inactivation is necessary for production of both sterigmatocystin, an aflatoxin precursor, and conidial development in A. nidulans [3]
We found that of the 38 genes significantly downregulated two-fold or more compared to the parental strain, many were genes predicted to encode either membrane-bound proteins or transcription factors involved in regulation of developmental processes and suggest that these changes interfere with normal conidiophore development and formation of the specific organelles required for AF formation
Summary
Formation of the asexual reproductive structure called a conidiophore in Aspergillus species requires the concerted activity of a number of transcription factors and signaling proteins. FlbA encodes a transcription factor that regulates the response to FluG. These proteins modulate the master transcription factor for conidial development, BrlA, a zinc-binding protein with two Cys2His domains [1,2]. In mutants of brlA, spores are not produced and the conidiphore stalks elongate to give a bristle appearance. Other genes involved in conidiophore development are stuA (stunted) and medA (medusa). These are required for proper spatial orientation of the conidophores
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