The T3S effector XopXccN of Xanthomonas campestris pv. campestris is involved in plant defense through interference with photosystems, reactive oxygen species (ROS) generation, and callose deposition

XopXccN and XopN are important type III secreted (T3S) virulence effector proteins ofXanthomonas campestris pv. campestris (Xcc) and Xanthomonas campestris pv.vesicatoria (Xcv), respectively. They were placed in the same T3S effector class based on sequence homology. It has been demonstrated that Xcv XopN suppresses pathogen-associated molecular pattern-triggered immune responses during Xcv infection. Here, we present evidence showing that Xcv XopN cannot replace XopXccN for the virulence ofXcc. In addition, we employed two-dimensional different gel electrophoresis to investigate the differentially expressed proteins affected by Xcc XopXccN in the host plant Chinese radish. The results demonstrated that nine proteins mainly associated with plant photosystems were suppressed by XopXccN. RT-PCR analysis showed that several proteins were repressed by XopXccN at the transcriptional level. Moreover, XopXccN could suppress the generation of reactive oxygen species (ROS) and callose deposition in plants. Taken together, our results revealed that XopXccN is involved in plant defense through interference with photosystems, ROS generation, and callose deposition in planta.   Key words: XopXccN, T3S effector, Xanthomonas campestris pv. campestris, 2D-DIGE.