Heterologous expression of the Brassica rapa transcription factor BrWRKY7 enhances resistance against bacterial soft rot caused by Pectobacterium carotovorum in Arabidopsis

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is one of the most widely consumed vegetables cultivated worldwide, including Republic of Korea, and can be seriously damaged by bacterial soft rot disease, leading to major crop loss during storage and cultivation. The necrotrophic bacterium Pectobacterium carotovorum ssp. carotovorum (Pcc) causes bacterial soft rot. In this study, we show that Brassica WRKY7 (BrWRKY7) transcription factor was induced by Pcc infection, and we analyzed its function during Pcc infection in Arabidopsis thaliana by generating the transgenic plants in which BrWRKY7 was heterologously expressed. Upon infection by Pcc of transgenic Arabidopsis plants constitutively overexpressing BrWRKY7, bacterial growth was inhibited and disease symptoms were significantly reduced compared to wild type, indicating that BrWRKY7 may play a role in defense responses to Pcc in Arabidopsis. Moreover, a defense marker gene, PDF1.2, was highly induced in BrWRKY7 overexpression transgenic plants, implying that BrWRKY7 is involved in the jasmonic acid (JA)-related defense pathway. The YFP-BrWRKY7 protein was exclusively localized in the nucleus in Arabidopsis protoplasts. These results demonstrate that pathogen-induced BrWRKY7 enhances disease resistance to Pcc in Arabidopsis, and works effectively as a positive transcription factor for the expression of defense-related genes. The discovery of the interesting gene BrWRKY7, isolated from Brassica rapa, which is able to activate defense responses to Pcc infection, may help to develop pathogen-resistant crops using this application.