Analyses of rice WRKY gene expression and OsWRKY13 DNA-binding activity. (a) and (c). Expression patterns of WRKY and OsWRKY13-activated genes genes after inoculation of Xoo strain PXO61 at booting stage. Samples were obtained before (ck) and at 2 and 4 d after pathogen inoculation. The expression level of each gene in transgenic plants was calculated relative to that in non-inoculated wild-type plants. Circle indicates a significant difference (P < 0.05) between non-inoculated and inoculated plants and asterisk indicates a significant difference (P < 0.05) between the transgenic plant and corresponding wild type within the same treatment. Bars represent mean (three replicates) ± standard deviation. (b) Yeast one-hybrid assay using OsWRKY13 as target protein and target DNA fragments from the promoters of rice WRKY genes and three other genes as baits. +, positive control; -, negative control; pW17HIS2, OsWRKY13 promoter fragment without W-box. All experiments were performed twice with similar results.