BcTCP22-BcTEM1 module suppresses flowering by regulating BcFT in Pak-choi

Transition from vegetative phase to reproductive growth at the appropriate time is critical for the success of sexual reproduction. Several Teosinte Branched 1/Cycloidea/Proliferating Cell Factors (TCPs) have been reported to regulate flowering. However, the functions of flowering regulation mediated by TCPs in Pak-choi remain largely unknown. Here, we identified and characterized a new flowering repressor in Pak-choi. BcTCP22 was localized in the nucleus and its expression was enriched in flowers and leaves. Overexpression of BcTCP22 exhibited late flowering, while silencing BcTCP22 led to early flowering. Accordingly, the expression of FT was reduced and increased, respectively. Y2H, BiFC and LCI assays indicated that BcTCP22 could interact with BcTEM1. BcTEM1 was localized in the nucleus and primarily expressed in leaves and stems. Overexpressing and silencing BcTEM1 showed late-flowering and early-flowering phenotype with down-regulated and up-regulated FT expression, respectively. EMSA and LUC assays revealed that both BcTCP22 and BcTEM1 repress BcFT by directly binding to its promoter. Furthermore, the interaction between BcTCP22 and BcTEM1 enhanced BcTCP22's ability to inhibit BcFT expression, leading to a lower level of BcFT. In conclusion, this work revealed the mechanism of flowering regulation by the BcTCP22-BcTEM1-BcFT module, which may lay a foundation for future investigation on other TCPs and provide new candidate genes for breeding late-flowering varieties of Pak-choi.