A reverse chromatin immunoprecipitation technique based on the CRISPR–dCas9 system

Abstract DNA–protein interaction is one of the most crucial interactions in biological processes. However, the technologies available to study DNA–protein interactions are all based on DNA hybridization; however, DNA hybridization is not highly specific and is relatively low in efficiency. RNA-guided DNA recognition is highly specific and efficient. To overcome the limitations of technologies based on DNA hybridization, we built a DNA-binding protein capture technology based on the clustered regularly interspaced palindromic repeats (CRISPR)–dead Cas9 (dCas9) system and transient genetic transformation, termed reverse chromatin immunoprecipitation based on CRISPR–dCas9 system (R-ChIP–dCas9). In this system, dCas9 was fused with Strep-Tag II to form a fusion protein for StrepTactin affinity purification. Transient transformation was performed for the expression of dCas9 and guide RNA (gRNA) to form the dCas9–gRNA complex in birch (Betula platyphylla) plants, which binds to the target genomic DNA region. The dCas9–gRNA–DNA complex was crosslinked, then the chromatin was sonicated into fragments, and purified using StrepTactin beads. The proteins binding to the target genomic DNA region were identified using mass spectrometry. Using this method, we determined the upstream regulators of a NAM, ATAF, and CUC (NAC) transcription factor (TF), BpNAC090, and 32 TFs potentially regulating BpNAC090 were identified. The reliability of R-ChIP–dCas9 was further confirmed by chromatin immunoprecipitation, electrophoretic mobility shift assays, and yeast one-hybrid. This technology can be adapted to various plant species and does not depend on the availability of a stable transformation system; therefore, it has wide application in identifying proteins bound to genomic DNA.