Modifying meiotic recombination by targeting chromatin regulators to crossover hotspots in Arabidopsis.

The impact of specific chromatin modifications on meiotic crossover frequency has typically been inferred from correlative studies, leaving the question of causality unresolved. To directly test this, we used a catalytically inactive CRISPR-associated protein 9 (dCas9)-based system to recruit the histone demethylase JMJ14 to defined genomic loci. Recruitment of JMJ14 led to a reduction in local histone H3 lysine 4 trimethylation (H3K4me3) levels and a decrease in crossover frequency within the targeted interval. This was accompanied by reduced expression of a long noncoding RNA (lncRNA) at the hotspot and altered crossover topology. Suppressed recombination was also observed at neighboring, untargeted hotspots. In contrast, targeting the transcriptional activator VP64 to the same region increased lncRNA expression, elevated crossover frequency, and raised H3K4me3 levels. Together, these findings establish a causal link between H3K4me3, transcription, and local crossover activity, demonstrating that H3K4me3 levels are closely associated with both transcriptional output and recombination frequency at specific genomic loci.