Abstract
The Pal/PacC pathway, which regulates genes that adapt to alterations in ambient pH, has been extensively studied in Aspergillus nidulans. Currently, the functions of the Pal/PacC pathway in Fusarium graminearum are poorly understood. In this study, we constructed targeted deletions of Pal/PacC pathway components through homologous recombination, including FgPalA, FgPalB, FgPalC, FgPalF, FgPalH, FgPalI and the pH-responsive transcription factor FgPacC. The phenotypic assay results indicated that the aerial hyphae of the ΔFgPalA, ΔFgPalB, ΔFgPalC, ΔFgPalF, ΔFgPalH and ΔFgPacC mutants of F. graminearum were significantly decreased in the PDA, MM and CM media and exhibited increased sensitivity to various environmental stresses. In addition, the western blot analysis revealed that the key element FgPacC could be cleaved to the functional isoform FgPacC30 after being subjected to alkaline pH or, independently, NaCl-induced osmotic stress. Further studies elucidated the direct interactions between the essential components of this signaling pathway in F. graminearum for the first time and revealed that ambient-pH-dependent proteolytic activation regulates the subcellular localization of FgPacC. More importantly, we revealed that FgPacC30 inhibits the activity of the histone acetyltransferase FgGcn5, thus transcriptionally down-regulating the expression of the FgTRI1 gene and inhibiting DON biosynthesis. Overall, our study suggests that the pH regulatory system plays a critical role in the response to external stress and virulence in F. graminearum, providing a new perspective for understanding the pathogenic mechanisms in phytopathogenic fungi.