The diverse functions of Pseudomonas syringae syringae van Hall effectors in regulating the plant immune response

Sorghum relies on its immune system to defend against various pathogens, including Pseudomonas syringae syringae van Hall (Pss van Hall). However, the sorghum immune system is largely unknown. Reports on pathogenic effectors have provided valuable insights into the plant immune system; thus, we aimed to identify Pss van Hall effectors that can regulate the sorghum defense response in this study. Here, we first established the sorghum-Pss van Hall pathosystem and found that type III effectors played critical roles in the virulence of Pss van Hall to sorghum. To predict its effectors, the whole genome of Pss van Hall was sequenced, and 18 effector-coding genes were identified. Among them, five effectors belong to the core effectors of Pseudomonas syringae pathovars, and two may be monocot pathogen-specific effectors. Pss van Hall triggered the hypersensitive response (HR) in Nicotiana benthamiana. We found that the effectors of Pss van Hall can be divided into cell death inducers and immune repressors by examining their functions in HR induction and repression of PTI marker gene, ROS production, and pathogen growth. Finally, the roles of core effectors HopAJ2 and HopAN1, and specific effector HopAX1 were further confirmed in the sorghum-Pss van Hall pathosystem. Importantly, the functions of HopAN1 and HopAX1 in regulating plant immunity were reported for the first time. We believe that the identification of these effectors will facilitate the continued exploration of the sorghum immune system.