Abstract
Rice WRKY45 is a transcription factor that plays an essential role in BTH-induced disease resistance in rice. Transgenic rice plants overexpressing WRKY45 (WRKY45-ox) exhibit strong resistance to blast and leaf-blight diseases. Whereas constitutive defense responses often cause severe growth defects in plants, WRKY45-ox rice shows only minor growth retardation; thus WRKY45 is expected for its utility in developing multi-disease resistance rice.
To characterize post-translational regulation of WRKY45, we generated transgenic rice overexpressing myc-tagged WRKY45 and analyzed the responses of myc-WRKY45 proteins to phytohormones and inhibitors. Proteasome inhibitor MG132 specifically induced high-level accumulation of myc-WRKY45. Immunoprecipitation assay using anti-polyubiquitin antibody revealed that myc-WRKY45 was polyubiquitinated in vivo. These results suggest that WRKY45 is post-translationally regulated by ubiquitin-proteasome pathway. Furthermore, we found that dephosphorylated myc-WRKY45 was more stable than its phosphorylated form, which suggests that protein phosphorylation is involved in the ubiquitin-proteasome regulation of WRKY45.
