Identification of WRKY22 direct targets under submergence in Arabidopsis with ChIP

To identify direct targets of WRKY22, we created a transgenic Arabidopsis line that expresses a c-myc epitope-tagged WRKY22 and used ChIP followed by microarray hybridization (ChIP-chip) to screen for candidates and validate the in vivo protein-DNA interactions with ChIP followed by quantitative PCR (ChIP-Q-PCR). The WRKY22 and c-myc epitope tag fusion construct was generated and transformed into wrky22-ko2 plants. The resulting transgenic lines should have better ChIP efficiency than the wild-type background, due to the reduced competition for WRKY22 binding sites from endogenous WRKY22. ChIP-enriched DNA fragments were identified using criteria of a window of +300 to －1200 of a gene for a promoter, a width of 4 probes or more, and a false discovery rate (FDR) < 0.1. The ChIP-chip experiments were repeated six times, i.e., six biological replicas. Candidates were defined by the presence of the promoter in three out of six biological replicas. Candidates were then classified based on their hypoxic responsiveness with a positive response defined as gene expression levels exhibiting > 2 or < 0.5-fold induction in any time point under submergence treatments in expression array data. Comparison of c-myc tagged WRKY22 transgenic plants vs wild-type (Columbia) plants. Both materials were submergence treated for 3 hours.