NirA is a key regulator mediating growth and development, patulin biosynthesis and pathogenicity in Penicillium expansum

NirA , a key regulator of nitrate assimilation, is involved in nitrogen signaling, but its role in Penicillium expansum remains poorly understood. In this study, we characterized NirA by bioinformatic analysis and constructed a PeNirA deletion mutant. Loss of PeNirA markedly impaired colony growth, sporulation, and hyphal development, accompanied by reduced expression of the conidiation-related genes abaA , brlA , and vosA . The mutant also showed a diminished ability to utilize a range of nitrogen sources. Patulin accumulation was substantially reduced both in vitro and in vivo , together with pronounced downregulation of key genes in the patulin biosynthetic cluster. In addition, deletion of PeNirA attenuated virulence on apple and pear fruit and affected the expression of PL , PLC , PME , and LOX in apple fruit during infection. Transcriptome analysis revealed extensive transcriptional changes in pathways associated with nitrogen metabolism, secondary metabolism, and redox processes, indicating that PeNirA deletion triggers broad regulatory effects. Taken together, these findings demonstrate that PeNirA contributes to the regulation of growth and development, nitrogen utilization, patulin biosynthesis, and pathogenicity in P. expansum .