BrSWN mutation reduces the H3K27me3 level at the BrFLC2 and BrFLC3 loci and confers a late-bolting phenotype in Chinese cabbage

Abstract

Flowering is an important developmental transition from the vegetative to the reproductive phase in plants. The role of histone modifications in the regulation of flowering time is well documented; however, their role in Chinese cabbage remains unclear. In the present study, we investigated a Chinese cabbage late-bolting mutant, M1407, which displayed a late-bolting time phenotype after vernalization. MutMap, kompetitive allele-specific PCR (KASP), and RNA interference (RNAi) analyses demonstrated that BrSWN, which encodes a catalytic subunit of the Polycomb repressive complex 2 (PRC2), mediates the flowering time in Chinese cabbage. BrSWN was functionally conserved and localized to the nucleus. Both BrSWN and Brswn interacted with BrVRN2 to form PRC2-like complexes. The BrSWN mutation decreased the global histone H3 lysine 27 trimethylation (H3K27me3) level and impaired the enrichment of H3K27me3 in the regions of flowering repressors, BrFLC2 and BrFLC3. This study demonstrates that BrSWN mediates the regulation of bolting time modulated by H3K27me3 deposition, providing insights into the epigenetic mechanisms regulating flowering time in Chinese cabbage.