The bZIP Transcription Factor AflRsmA Regulates Aflatoxin B1 Biosynthesis, Oxidative Stress Response and Sclerotium Formation in Aspergillus flavus

Fungal secondary metabolites play important roles not only in fungal ecology but also in humans living as beneficial medicine or harmful toxins. In filamentous fungi, bZIP-type transcription factors (TFs) are associated with the proteins involved in oxidative stress response and secondary metabolism. In this study, a connection between a bZIP TF and oxidative stress induction of secondary metabolism is uncovered in an opportunistic pathogen Aspergillus flavus, which produces carcinogenic and mutagenic aflatoxins. The bZIP transcription factor AflRsmA was identified by a homology research of A. flavus genome with the bZIP protein RsmA, involved in secondary metabolites production in Aspergillus nidulans. The AflrsmA deletion strain (Delta AflrsmA) displayed less sensitivity to the oxidative reagents tert-Butyl hydroperoxide (tBOOH) in comparison with wild type (WT) and AflrsmA overexpression strain (AflrsmA(OE)), while AflrsmA(OE) strain increased sensitivity to the oxidative reagents menadione sodium bisulfite (MSB) compared to WT and Delta AflrsmA strains. Without oxidative treatment, aflatoxin B-1 (AFB(1)) production of Delta AflrsmA strains was consistent with that of WT, but AflrsmA(OE) strain produced more AFB(1) than WT; tBOOH and MSB treatment decreased AFB(1) production of Delta AflrsmA compared to WT. Besides, relative to WT, Delta AflrsmA strain decreased sclerotia, while AflrsmA(OE) strain increased sclerotia. The decrease of AFB(1) by Delta AflrsmA but increase of AFB(1) by AflrsmA(OE) was on corn. Our results suggest that AFB(1) biosynthesis is regulated by AflRsmA by oxidative stress pathways and provide insights into a possible function of AflRsmA in mediating AFB(1) biosynthesis response host defense in pathogen A. flavus.