Pigment biosynthesis pathway in <i>Aspergillus ustus</i> : a comprehensive analysis combining transcriptomics and chemical intervention

The Aspergillus ustus pigment production was investigated by introducing different precursor and enzyme inhibitors during the early biosynthesis stages. A comparative transcriptomic analysis was conducted between pigment-producing and non-producing A. ustus strains. Bioinformatics approaches were employed to functionally annotate and perform enrichment analysis of the sequenced genes. Reverse transcription quantitative PCR (RT-qPCR) was used to validate the transcriptome sequencing results. The addition of acetic acid, propionic acid, isoleucine, arginine, methionine and phenylalanine enhanced pigment production, whereas iodoacetamide, dinitrofluorobenzene, P-aminobenzoic acid and imidazole inhibited it. Transcriptomic analysis revealed significant differential gene expression during pigment biosynthesis, including pronounced upregulation of genes related to non-reducing polyketide synthase (NR-PKS). Integrative evidence reveals that A. ustus pigment is synthesized via an iterative type I PKS pathway catalyzed by fungal NR-PKSs, similar to the noranthrone biosynthetic pathway in fungi. RT-qPCR validation showed 80% concordance with the RNA-seq data, confirming the reliability of the transcriptome sequencing.