Regulation of hydrogen peroxide accumulation and death of Agrobacterium-transformed cells in tomato transformation

Our previous studies demonstrate that Agrobacterium causes tissue browning that subsequently reduces transformation efficiency in tomato transformation. In addition application of lipoic acid (LA) can reduce tissue browning and increase transformation efficiency in different crops. A major challenge in Agrobacterium-mediated plant transformation is the death of Agrobacterium-transformed cells (DATC), which restricts transgenic plant production. Hydrogen peroxide (H2O2) plays a critical role in oxidative stress. However, little is known about the biochemical and molecular mechanisms for DATC. Our biological and correlation analyses showed that Agrobacterium mediated H2O2 accumulation (HOA) and HOA elevation led to DATC during Agrobacterium-mediated tomato cv. MicroTom transformation. Agrobacterium significantly (P < 0.05) increased 4.2- and 1.4-fold expression of WRKY75 (a H2O2-responsive transcription factor) and superoxide dismutase (SOD), respectively, while the application of 4.4 M H2O2 significantly increased 19- and 2.7-fold expression of WRKY75 and 2-cys peroxiredoxin (Cys), respectively, and decreased fivefold SOD expression, compared with a control. LA application significantly (P < 0.05) reduced 1.6-fold HOA and DATC while it significantly increased 1.7-fold expression of Cys, and reduced 2.2- and 1.4-fold expression of WRKY75 and SOD, respectively. The reduction of HOA and DATC was accompanied by suppression of WRKY75 and SOD and activation of Cys. Our results indicated that DATC was regulated by H2O2 that was triggered by Agrobacterium and LA application through their gene regulation. In addition, HOA was associated with a biotic generating reactive oxygen species (ROS) mechanism, and HOA and DATC were likely regulated by an enzymatic ROS scavenging mechanism during Agrobacterium-mediated tomato transformation.