Distinctive functions of bZIP factors PeAP1 and PeAtf1 in regulating growth, virulence, stress response, and metabolism of Penicillium expansum

The basic leucine zipper (bZIP) family is crucial in regulating growth, stress response and pathogenicity of phytopathogenic fungi. However, its information is limited in Penicillium expansum, the causal agent of apple blue mold disease. In this study, a bZIP transcription factor PeAP1 was identified in P. expansum through a gene replacement strategy. Results showed that ΔPeAP1 exhibited significant growth defects, reduced virulence, and altered tolerance to osmotic, cell wall, oxidative, and cold stresses. Notably, ΔPeAP1 showed complete growth inhibition under H₂O₂ treatment, with partial restoration of growth and pathogenicity upon antioxidant supplementation, indicating the contribution of PeAP1 to fungal growth and virulence via regulating oxidative stress response. Furthermore, we compared the role of PeAP1 and another bZIP transcription factor PeAtf1, a negative regulator of PeAP1 and antioxidant ability, as indicated by our previous study. Results showed that both PeAP1 and PeAtf1 mediated carbon and nitrogen metabolism. PeAtf1, rather than PeAP1, positively regulates the production of patulin by controlling the patulin gene cluster. These findings provide novel insights into bZIP-mediated regulation in P. expansum and can help develop strategies for controlling postharvest diseases and patulin contamination caused by P. expansum in the future.