A histone H4 gene prevents premature bolting by attenuating photoperiodic flowering genes under drought conditions in Chinese cabbage

Flowering is one of the most important traits in Chinese cabbage because premature flowering reduces yield and quality of the harvested products. Water deficit, caused by drought or other environmental conditions, can induce early flowering. Drought resistance involves global reprogramming of transcription, hormone signaling, and chromatin modification. How these regulatory responses are coordinated via the various pathways is largely unknown. We show that a histone H4 protein, BrHIS4.A04, physically interacts with a homeodomain protein BrVIN3.1 that was selected during the domestication of late-bolting Chinese cabbages. Over-expression of BrHIS4.A04 resulted in drought hypersensitivity and premature flowering under normal conditions but prevented premature bolting under drought conditions. We show that the expression of key ABA signaling genes (ABI1, MYC2, ABA1, and NCED3), and also photoperiodic flowering genes (GI, FT, and SOC1) was attenuated by BrHIS4.A04 under drought conditions. Furthermore, the level of H4-acetylation at these gene loci was hampered in BrHIS4.A04OE plants. BrHIS4.A04 prevents premature bolting by attenuating photoperiodic flowering genes under drought conditions through the ABA signaling pathway. Since BrHIS4.A04OE plants displayed no phenotypes related to vegetative or reproductive development under drought, our findings will contribute to fine-tuning of the flowering time in crops with no growth penalty through genetic engineering.