Inoculation with Trichoderma atroviride and T. virens Induces ROS Overaccumulation and Compromises Pathogen Resistance in Arabidopsis 35S::TaEPL1-3 Plants

Recent studies showed that constitutive expression of the cerato-platanin protein EPL1 from Trichoderma atroviride in the Arabidopsis thaliana 35S::TaEPL1-3 line promotes plant growth and pathogen resistance. Here, the effect of inoculating this line with T. atroviride and T. virens on growth and defense responses was evaluated. Inoculated 35S::TaEPL1-3 plantlets exhibited increased fresh weight and more lateral roots compared to uninoculated controls. Infection assays on 28-day-old 35S::TaEPL1-3 and Col-0 (WT) leaves (pre-inoculated at 15 days with T. atroviride, T. virens, or both) revealed that dual Trichoderma inoculation compromised the transgenic line’s resistance to Pseudomonas syringae and Botrytis cinerea compared to WT. It was previously reported that the 35S::TaEPL1-3 line accumulates elevated levels of reactive oxygen species (ROS). Therefore, ROS levels were examined to determine whether they were further influenced by inoculation with Trichoderma species. Dual inoculation triggered higher H2O2 accumulation in 35S::TaEPL1-3 compared to WT. In addition, high ROS levels were observed when the 35S::TaEPL1-3 line was co-inoculated with both Trichoderma species and subsequently challenged with both pathogens. These findings showed that elevated ROS levels may compromise priming activation in the 35S::TaEPL1-3 line (constitutively expressing the Epl1 elicitor) during co-inoculation with T. atroviride (Epl1-secreting) and T. virens (Sm1-secreting), where synergistic elicitor accumulation could potentially lead to defense signal dysregulation and consequent loss of resistance in transgenic plants.