Hydrogen cyanamide enhances flowering time in tea oil camellia (Camellia oleifera Abel.)

Appropriate flowering time is one of the most important traits for oilseed production and crop yield in tea oil camellia (Camellia oleifera Abel.). It secures the availability of pollinators and balances the growth period after flowering with respect to cold winter temperatures and rainfall. However, the effective regulator of flowering time and its mechanisms in C. oleifera are not clearly understood. This study demonstrates that hydrogen cyanamide (HC), rather than gibberellin A3, gibberellin A4+7, thidiazuron, or 6-benzylaminopurine, acts as a potentially effective agent to promote flowering time by ~12 days. Accumulation of indole acetic acid, ethylene, salicylic acid, and reactive oxygen species (ROS) in floral buds of C. oleifera was significantly increased by HC treatment. Transcriptome analysis suggested that exogenous HC application promoted flowering via regulating genes involved in auxin metabolism, ethylene-MAPK (mitogen-activated protein kinase) signaling, and ROS metabolism. These results demonstrate that HC can advance flowering by enhancing cell expansion, cell cycle progression, and flower development in floral buds. These findings help understand the role of HC in flowering regulation in autumn/winter-flowering perennials and provide new insights into the potential utilization of HC as a flower inducer in C. oleifera cultivation.