Gene transcription is governed by a complex regulatory system involving changes in chromatin structure, the action of transcription factors, and the activation of cis-regulatory elements. Postharvest fruits are threatened by Penicillium expansum, a leading causal agent of blue mold disease and one of the most economically significant postharvest pathogens worldwide. However, information on its transcription regulatory mechanism is lagging. Here, we conducted an assay for transposase accessible chromatin sequencing (ATAC-seq) for P. expansum during vegetative growth and infection phase and then studied the function of a basic leucine zipper (bZIP) transcription factor PeAtf1. Results highlighted the role of promoter regions in gene transcription and the significant difference in P. expansum between these two phases. Six footprint-supported cis-regulatory elements of active transcription factors were obtained and analyzed. We then identified a homolog of the bZIP regulator Atf1, PeAtf1, and found it positively regulated vegetative growth, reproduction, and osmotic stress response in P. expansum. Furthermore, PeAtf1 deletion enhanced the fungus's tolerance to oxidative, cell wall, and membrane stresses, which might contribute to the virulence of deletion mutants in apple fruits, leading to similar pathogenicity between mutants and the wild type. Overall, this study provides new insights into the transcription regulatory profile of P. expansum, aiding in the future development of strategies to control P. expansum.

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