TrPLD1 and TrPLD2 modulate reactive oxygen species production and pathogenicity in Trichothecium roseum infected apple fruit

Phospholipase D (PLD) plays an important role during pathogen-host interaction, which not only hydrolyzes the phosphodiester bond in the phospholipid structure of the host cell membrane, resulting in the cell membrane structure destruction of the host, but also produces phosphatidic acid that can interact with NADPH oxidase (NOX) on the cell plasma membrane, resulting in reactive oxygen species (ROS) accumulation and improving the pathogenicity of the pathogen. However, the ROS production of filamentous fungi by PLD modulation and its pathogenicity on postharvest fruit and vegetables have not been documented. In this study, we constructed ΔTrPLD1 and ΔTrPLD2 mutants and complement strains of Trichothecium roseum by homologous recombination, and analyzed ROS production and its pathogenicity on apple fruit. The results showed that the deletion of TrPLD1 and TrPLD2 increased the sensitivity to oxidative stress and reduced ROS production of T. roseum mycelia. During ΔTrPLD1 mutant of T. roseum infecting apple fruit, the gene expression and activity of NOX decreased, which lead to the reduction of superoxide anion production rate. The gene expressions and activities of superoxide dismutase and peroxidase were up-regulated, the expression and activity of catalase were down-regulated, and the activation of ascorbic acid-glutathione cycle, ultimately enhanced the production of H2O2 in apple tissue, H2O2 acted as signal molecule to trigger disease resistance of fruit, thereby reducing the pathogenicity on apple fruit. The ΔTrPLD2 mutant had no significant effect on ROS production during pathogen infecting apple fruit. In summary, ΔTrPLD1 and ΔTrPLD2 mutants were highly sensitive to oxidative stress, and TrPLD1 played more important role in T. roseum infected apple fruit by regulating ROS production.