AoZC9, a Zn(II)2Cys6 transcription factor, negatively regulates salt tolerance in Aspergillus oryzae by controlling fatty acid biosynthesis

Aspergillus oryzae , a key fermenting organism in soy sauce production, faces significant osmotic stress due to high environmental salt levels. This study identifies and functionally characterizes a novel Zn(II) ₂ Cys ₆ transcription factor, AoZC9, which negatively regulates salt tolerance by controlling fatty acid biosynthesis. Overexpression of AoZC9 decreased growth rates in the presence of salt, while its knockdown enhanced growth, spore count, and biomass, particularly under conditions of 15% salt concentration, doubling these metrics compared to the wild-type. Furthermore, overexpression of AoZC9 led to the downregulation of the FAD2 gene, a key enzyme in unsaturated fatty acid biosynthesis. Transcriptome analysis revealed the broad impact of AoZC9 on unsaturated fatty acid biosynthesis and key stress response pathways, emphasizing its regulatory role in the mitogen-activated protein kinase signaling pathway and the ABC transporters pathway, both integral to cellular osmotic balance and endoplasmic reticulum homeostasis. These findings offer valuable insights into the molecular underpinnings of salt stress response and could inform improvements in industrial fermentation processes for Aspergillus oryzae .