Location: Food and Feed Safety ResearchTitle: Kojic acid gene clusters and the transcriptional activation mechanism of Aspergillus flavus KojR on expression of clustered genes
|Chang, Perng Kuang|
|SCHARFENSTEIN, LESLIE - Retired ARS Employee|
|MAHONEY, NOREEN - Retired ARS Employee|
|KONG, QING - Ocean University Of China|
Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2023
Publication Date: 2/15/2023
Citation: Chang, P.-K., Scharfenstein, L.L., Mahoney, N., Kong, Q. 2023. Kojic acid gene clusters and the transcriptional activation mechanism of Aspergillus flavus KojR on expression of clustered genes. The Journal of Fungi. 9:259. https://doi.org/10.3390/jof9020259.
Interpretive Summary: Kojic acid is a fungal secondary metabolite. It has long been used as a skin-whitening agent. It is also used as an antioxidant to prevent enzymatic browning to extend shelf life of fruits and vegetables. Additionally, kojic acid and its derivatives possess anti-bacterial, anti-fungal, anti-inflammatory and antineoplastic properties. Therefore, it has wide applications in cosmetics, food, and pharmaceutical industries. In this work, we showed how kojic acid biosynthesis was controlled by genetic factors. The knowledge gained will help to optimize future kojic acid production.
Technical Abstract: Kojic acid (KA) is a fungal metabolite and has a variety of applications in cosmetics and food industries. Aspergillus oryzae is a well-known producer of KA, and its KA biosynthesis gene cluster has been identified. In this study, we showed that nearly all section Flavi aspergilli except for A. avenaceus had complete KA gene clusters and only one Penicillium species, P. nordicum, contained a partial KA gene cluster. Phylogenetic inference based on KA gene cluster sequences consistently grouped section Flavi aspergilli into clades as prior studies. For A. flavus, the Zn(II)2Cys6 zinc cluster regulator KojR transcriptionally activated clustered genes of kojA and kojT. This was evidenced by time-course expression of both genes in kojR-complemented strains whose kojR expression was driven by heterologous Aspergillus nidulans gpdA promoter or homologous A. flavus gpiA promoter. Using sequences from kojA and kojT promoter regions of section Flavi aspergilli for motif analyses, we identified a consensus KojR-binding motif to be a 11-bp palindromic sequence of 5’-CGRCTWAGYCG-3’ (R =A/G, W=A/T, Y=C/T). We showed in A. flavus by using a CRISPR/Cas9-mediated gene-targeting technique that only the motif sequence, 5’-CGACTTTGCCG-3’, in the kojA promoter was critical for KA biosynthesis. Therefore, kojA and kojT are regulated differently.