A nuclease-dead Cas9-derived tool represses target gene expression.

Manipulation of gene expression is central to understanding gene function, engineering cell behavior, and altering biological traits according to production demands. Nuclease-dead Cas9 (dCas9), a variant of active Cas9, offers a versatile platform for the precise control of genome function without DNA cleavage. Notably, however, an effective and universal dCas9-based transcriptional repression system remains unavailable in plants. The noncanonical histone acetyltransferase TENDRIL-LESS (CsTEN) is responsible for chromatin loosening and histone modification in cucumber (Cucumis sativus). In this study, we engineered a gene regulation tool by fusing TEN and its truncated proteins with dCas9. The full-length dCas9-TEN protein substantially repressed gene expression, with the N-terminal domain identified as the core repression domain. We subsequently validated the specificity and efficacy of this system through both transient infection and genetic transformation in cucumber and Arabidopsis (Arabidopsis thaliana). The electrophoretic mobility shift assay (EMSA) revealed the ability of the N-terminal domain of TEN to bind to chromatin, which may promote target binding of the dCas9 complex and enhance the transcriptional repression effect. Our tool enriches the arsenal of genetic regulation tools available for precision breeding in crops.