GBF 1 differentially regulates CAT 2 and PAD 4 transcription to promote pathogen defense in Arabidopsis thaliana

Summary G‐ BOX BINDING FACTOR 1 ( GBF 1) influences light‐regulated seedling development in Arabidopsis, and inhibits CATALASE 2 ( CAT 2 ) expression during senescence. CAT 2 functions as a scavenger of hydrogen peroxide. The role of GBF 1 in the defense response is not known. We report here that GBF 1 positively influences the defense against virulent and avirulent strains of Pseudomonas syringae . The gbf1 mutants are susceptible, whereas GBF 1 over‐expresser transgenic plants are resistant to bacterial pathogens. GBF 1 negatively regulates pathogen‐induced CAT 2 expression and thereby positively regulates the hypersensitive response. In addition to CAT 2 promoter, GBF 1 binds to the G‐box‐like element present in the intron of PHYTOALEXIN DEFICIENT 4 ( PAD 4 ). This association of GBF 1 with PAD 4 intron is enhanced upon pathogenesis. GBF 1 positively regulates PAD 4 transcription in an intron‐dependent manner. GBF 1‐mediated positive regulation of PAD 4 expression is also evident in gbf1 mutant and GBF 1 over‐expression lines. Similar to pad4 mutants, pathogen‐induced camalexin and salicylic acid ( SA ) accumulation, and expression of SA ‐inducible PATHOGENESIS RELATED 1 ( PR 1 ) gene are compromised in the gbf1 mutant. Exogenous application of SA rescues the loss‐of‐defense phenotypes of gbf1 mutant. Thus, altogether, our results demonstrate that GBF 1 is an important component of the plant defense response that functions upstream of SA accumulation and, by oppositely regulating CAT 2 and PAD 4 , promotes disease resistance in Arabidopsis.