Functional Analysis Of Arabidopsis WRKY2 Transcription Factor

Plant WRKY DNA-binding transcription factors are key regulators in certain developmental programs. A number of studies have suggested that WRKY genes may mediate seed germination and postgermination growth. However, it is unclear whether WRKY genes mediate ABA-dependent seed germination and postgermination growth arrest. In this study, we report that wrky2-1 and wrky2-2 T-DNA insertion mutants are hypersensitive to ABA responses only during germination and postgermination early growth, and they are more sensitive to NaCl and mannitol than wild type. Arabidopsis WRKY2 protein is nuclear-localized and specifically recognizes the TTGACC W-box sequences in vitro. The nuclear localization and sequence-specific DNA-binding activity support that WRKY2 functions as a transcription factor. Wrky2 mutants displayed delayed or decreased expression of ABI5 and ABI3, but increased or prolonged expression of Em1 and Em6. Wrky2 mutants and wild type showed similar levels of expression for miR159 and its target genes MYB33 and MYB101. ABA hypersensitivity of the wrky2 mutants during seed germination and postgermination early seedling establishment is attributable to elevated mRNA levels of ABI5, ABI3 and ABI5-induced Eml and Em6 in the mutants. WRKY2-mediated ABA responses are independent of miR159 and its target genes MYB33 and MYB101. Analysis of WRKY2 expression level in ABA-insensitive and ABA-deficient mutants abi5-1, abi3-1, aba2-3 and aba3-1 further indicated that ABA-induced WRKY2 accumulation during germination and postgermination early growth requires ABI5, ABI3, ABA2 and ABA3, and ABI5, ABI3, ABA2 and ABA3 are important regulators of the transcripts of WRKY2 by ABA treatment. Our results suggest that WRKY2 transcription factor mediates seed germination and postgermination developmental arrest by ABA.