Targeted editing of histone H3K27 trimethylation elucidates its significance in photoperiodic control of flowering

Epigenetic modifications play essential roles in regulating gene expression, yet establishing direct causality between specific modifications and transcriptional outcomes remains challenging. In this study, we employed a CRISPR/dCas9-SunTag system to specifically reduce H3K27me3 levels at the FLOWERING LOCUS T (FT) gene in Arabidopsis thaliana. Targeting a truncated version of the H3K27 demethylase REF6 lacking its DNA-binding zinc fingers (REF6?ZnF) to the FT locus effectively decreased local H3K27me3, enhanced FT transcription, and led to early flowering phenotypes, particularly under non-inductive short-day (SD) conditions. Chromatin immunoprecipitation confirmed the site-specific reduction of H3K27me3, with minimal genome-wide changes. Under long-day (LD) conditions, H3K27me3 levels at FT oscillated diurnally, coinciding with FT induction at dusk, while in SD conditions, H3K27me3 remained stable, contributing to FT repression. Our results provide direct evidence that H3K27me3 represses FT transcription under non-inductive conditions and demonstrate the utility of epigenetic editing for fine-tuning gene expression and developmental traits in plants Overall design: Examination of H3K27me3 enrichment in wild-type and transgenic seedlings