RNA sequencing of an nsdC mutant reveals global regulation of secondary metabolic gene clusters in Aspergillus flavus

The filamentous fungus, Aspergillus flavus (A. flavus) is an opportunistic pathogen capable of invading a number of crops and contaminating them with toxic secondary metabolites such as aflatoxins. Characterizing the molecular mechanisms governing growth and development of this organism is vital for developing safe and effective strategies for reducing crop contamination. The transcription factor nsdC has been identified as being required for normal asexual development and aflatoxin production in A. flavus. Building on a previous study using a large (L)-sclerotial morphotype A. flavus nsdC mutant we observed alterations in conidiophore development and loss of sclerotial and aflatoxin production using a nsdC mutant of a small (S)-sclerotial morphotype, that normally produces aflatoxin and sclerotia in quantities much higher than the l-morphotype. RNA sequencing analysis of the nsdC knockout mutant and isogenic control strain identified a number of differentially expressed genes related to development and production of secondary metabolites, including aflatoxin, penicillin and aflatrem. Further, RNA-seq data indicating down regulation of aflatrem biosynthetic gene expression in the nsdC mutant correlated with HPLC analyses showing a decrease in aflatrem levels. The current study expands the role of nsdC as a globally acting transcription factor that is a critical regulator of both asexual reproduction and secondary metabolism in A. flavus.