Sugar transport in tulip is modulated by TgRR12-TgTCP2 signaling through TgSUT4

Tulips, the economically important ornamental plants, are propagated primarily through vegetative renewal, with bulbs regenerating annually via the outgrowth of axillary buds. This process depends on precise coordination between carbohydrate allocation and phytohormone signaling However, the molecular mechanisms governing the regulatory networks remain less explored. Here, we identified the transcription factor TgTCP2 as a key mediator of cytokinin and sugar signaling pathways during tulip bulb development. Functional studies revealed that silencing TgTCP2 in tulip impaired sucrose transport and daughter bulb growth, whereas ectopic overexpression of TgTCP2 in Arabidopsis enhanced plant growth. Furthermore, we demonstrated that TgTCP2 promotes long-distance sucrose transport by directly binding to the promoter of TgSUT4, thereby fine-tuning carbohydrate allocation between source and sink tissues - a critical process for daughter bulb development. Additionally, TgTCP2 physically interacts with the type B cytokinin response regulator TgRR12, linking it to cytokinin signaling. Intriguingly, elevated cytokinin levels enhanced the physical interaction between TgRR12 and TgTCP2, which alleviated its binding activity to the promoter regions of TgSUT4, thereby suppressing sucrose transport. Our findings unveil a novel role for TgTCP2/TgRR12-TgSUT4 module in regulating sucrose transport and tulip daughter bulb development, providing new insights into cytokinin-mediated metabolic coordination during storage organ formation in tulip.