The Zn(II)2-Cys6-type zinc finger protein AoKap7 is involved in the growth, oxidative stress and kojic acid synthesis in Aspergillus oryzae.

Abstract

Although the kojic acid gene cluster in Aspergillus oryzae was identified in 2010, the functions of neighbouring genes remain poorly understood. Here, we characterise Aokap7, a gene adjacent to this cluster that encodes a novel nucleus-localised zinc finger protein without transcriptional activation activity. Disruption of Aokap7 markedly accelerated spore germination, hyphal growth, and conidial formation, but impaired kojic acid production. Overexpression of kojR or laeA restored kojic acid production in the Aokap7 disruption strain, whereas their disruption abolished it, indicating that Aokap7 regulates kojic acid production by kojR and laeA. Furthermore, disrupting Aokap7 in the AozfA overexpression or disruption strains reversed their kojic aicd production, suggesting that Aokap7 acts downstream of AozfA. The Aokap7 mutant also exhibited reduced expression of reactive oxygen species (ROS)-scavenging genes and heightened oxidative stress sensitivity. Biochemical assays revealed that Aokap7 preferentially binds to the motif 5'-CGGCTCGG-3', and directly interacts with the AoGPX1 promoter. Disruption of AoGPX1 increased the sensitivity of A. oryzae to oxidative stress. Our findings elucidate the pivotal role of Aokap7 in coordinating growth, oxidative stress response and kojic acid production, advancing understanding of the regulatory network of kojic acid synthesis in A. oryzae.