PacC mediated ammonia synthesis contributes to the pathogenicity of Trichothecium roseum by regulating reactive oxygen species and extracellular enzymes

The Pal signaling pathway plays an important role in the adaptation of pathogenic fungi to environmental pH fluctuations and consists of PalA, PalB, PalC, PalF, PalI, PalH and Pac C in filamentous fungi. As a key regulator of the Pal signaling pathway, the transcription factor PacC is involved in the regulation of ammonia synthesis, extracellular enzyme activity and pathogenicity of fungi. However, the effect of PacC on the Pal signaling pathway and the production of reactive oxygen species (ROS) in fungi is unknown. It is also unclear whether PacC is involved in the synthesis and transport of ammonia, the alkalinization of environmental pH and the regulation of extracellular enzyme gene expression in Trichothecium roseum. In this study, the wild-type strain, ΔPacC mutant and ΔPacC-C complement strains of T. roseum were used as material to analyze the role of TrPacC in the Pal pathway, ammonia accumulation and environmental pH regulation. Meanwhile, the effect of TrPacC on the pathogenicity of T. roseum was investigated by determining the production of ROS and the expression of extracellular enzyme genes. The results showed that deletion of TrPacC enhanced the pH signal perception and transduction by upregulating the expression of TrPalF and TrPalH, but downregulated the expression of TrPalC, TrPalA and TrPalB, which are involved in PacC activation. Deletion of TrPacC inhibited ammonia synthesis and secretion by downregulating the expression of TrGDH2, TrAMET, TrMEPB and TrGLT1, resulting in reduced ammonia accumulation and attenuated alkalization ability at ambient pH in vivo and in vitro. Deletion of TrPacC also reduced superoxide anion and hydrogen peroxide levels by downregulating TrNoxA expression, but had no significant effect on TrNoxB expression. In addition, deletion of TrPacC downregulated the expression of TrPG, TrPMG, TrPME, TrPL, TrPAL and TrCx and inhibited the lesion expansion of T. roseum on muskmelon and apple fruit. Taken together, deletion of TrPacC attenuated the pathogenicity of T. roseum in muskmelon and apple fruit by reducing the accumulation of ammonia and ROS and inhibiting the expression of extracellular enzyme genes.