Decreased ROS level and activation of antioxidant gene expression in Agrobacterium rhizogenes pRiA4-transformed calli of Rubia cordifolia

Microbe-plant interactions often lead to a decrease in the reactive oxygen species (ROS) level of plant cells, which allows pathogen survival through the suppression of plant immune responses. In the present investigation, we tested whether transformation of Rubia cordifolia cells by Agrobacterium rhizogenes had a similar effect. We isolated partial cDNA sequences of ascorbate peroxidase, catalase and Cu/Zn superoxide dismutase genes (RcApx1, RcApx2, RcApx3, RcCAT1, RcCAT2, RcCSD1, RcCSD2 and RcCSD3) from plant tissues, as well as pRiA4-transformed and normal calli of Rubia cordifolia, and studied their expression by real-time PCR. Transcription profiling revealed that ascorbate peroxidase (RcApx1) and Cu/Zn superoxide dismutase (RcCSD1) were the most abundant transcripts present in both plant tissues and non-transformed calli. Catalase genes were weakly expressed in these samples. The pRiA4-transformed calli showed enhanced expression of several genes encoding ROS-detoxifying enzymes. Confocal microscopy imaging revealed decreased ROS level in pRiA4-transformed calli compared to the control. These results demonstrate that A. rhizogenes, like other plant pathogens, uses a strategy aimed at decreasing ROS levels in host cells through the general upregulation of its antioxidant genes.