Transcription Factor AtMYB44 Regulates Induced Expression of the ETHYLENE INSENSITIVE2 Gene in Arabidopsis Responding to a Harpin Protein

AtMYB44 is a transcription factor that functions in association with the ethylene-signaling pathway in Arabidopsis thaliana. The pathway depends on ETHYLENE INSENSITIVE2 (EIN2), an essential component of ethylene signaling, to regulate defense responses in the plant following treatment with HrpN(Ea), a harpin protein from a bacterial plant pathogen. Here, we show that AtMYB44 regulates induced expression of the EIN2 gene in HrpN(Ea)-treated Arabidopsis plants. A HrpN(Ea) and ethylene responsive fragment of the AtMYB44 promoter is sufficient to support coordinate expression of AtMYB44 and EIN2 in specific transgenic Arabidopsis. In the plant, the AtMYB44 protein localizes to nuclei and binds the EIN2 promoter; the HrpN(Ea) treatment promotes AtMYB44 production, binding activity, and transcription of AtMYB44 and EIN2. AtMYB44 overexpression results in increased production of the AtMYB44 protein and the occurrence of AtMYB44-EIN2 interaction under all genetic backgrounds of wild-type Arabidopsis and the etr1-1, ein2-1, ein3-1, and ein5-1 mutants, which have defects in the ethylene receptor ETR1 and the signal regulators EIN2, EIN3, and EIN5. However, AtMYB44 overexpression leads to enhanced EIN2 expression only under backgrounds of wild type, ein3-1, and ein5-1 but not etr1-1 and ein2-1, suggesting that ethylene perception is necessary to the regulation of EIN2 transcription by AtMYB44.