Location: Food and Feed Safety ResearchTitle: Analysis of an nsdC mutant in Aspergillus flavus reveals an extensive role in the regulation of several secondary metabolic gene clusters Author
Submitted to: Fungal Genetics Conference/Asilomar
Publication Type: Abstract Only
Publication Acceptance Date: 3/19/2015
Publication Date: N/A
Technical Abstract: Aspergillus flavus is a saprophytic fungus that can invade and contaminate agronomically important crops. The fungus produces a number of toxic secondary metabolites, such as aflatoxin, which are synthesized from genes located in close proximity with each other on the chromosome. A. flavus has approximately 55 such gene clusters. NsdC is a C2H2-type transcription factor that has been shown to play a role in asexual development and aflatoxin production in this fungus. Previous data demonstrated that nsdC knockout mutants in the sclerotial L-morphotype A. flavus CA14 exhibited perturbed development of conidiophores, altered colony pigmentation and loss of sclerotia and aflatoxin production. To better determine the role of nsdC in the regulation of secondary metabolite production in A. flavus we conducted RNA-sequencing analysis using an nsdC knockout in the S-morphotype A. flavus SRRC 70 (Af70). These studies, combined with SMURF analysis, revealed that 83% of predicted secondary metabolic gene clusters had altered expression profiles in the nsdC knockout strain. Expression of genes in clusters responsible for penicillin, asparasone, ustiloxin B, and piperazine production were increased, whereas, genes responsible for aflatrem, aflatoxin, and kojic acid were decreased compared to that of the control. HPLC-MS analysis of fungal extracts showed decreased levels of the aflatrem metabolite present in the knockout strain corresponding with the gene expression data. Our analysis also revealed significant down regulation of a putative secondary metabolic gene cluster that is present in Af70 but not in found in other A. flavus isolates including the type strain NRRL 3357. This cluster contains genes predicted to encode a polyketide synthase, two p450s, a Zn(2)–Cys(6) transcription factor and other decorating enzymes. Analysis of these secondary metabolic gene profiles with special emphasis on the functional characterization of the novel gene cluster in Af70 will be discussed.