Transcription factor CsDREB28 regulates sugar transporters CsSWEET17 and CsSWEET15 to modulate cold resistance and plant growth in tea plants.

Cold stress limits the geographical distribution of tea plants (Camellia sinensis) and negatively affects tea quality and yield. Sugar plays an important role in the cold stress response of tea plants, and CsSWEET17 is a plasma membrane-localized sugar transporter that regulates plant growth and freezing resistance by mediating sugar allocation. In this study, we identified the upstream regulatory factor CsDREB28 of CsSWEET17, an ERF-associated amphiphilic repression protein strongly induced by cold stress that directly inhibits the transcription of CsSWEET17 under both normal and cold stress conditions. Transient silencing of CsDREB28 enhanced the freezing resistance of tea plants by upregulating the expression of the C-repeat-binding (CBF) transcriptional pathway and CsSWEET17 and promoting the accumulation of soluble sugars. Heterologous overexpression of CsDREB28 in Arabidopsis not only significantly reduced freezing resistance but also accelerated leaf senescence, inhibited plant growth, and decreased the seed-setting rate. Further research has shown that CsDREB28 negatively regulates CsSWEET15, a reproductive organ-specific gene, and its Arabidopsis homolog, AtSWEET15, which plays an important role in reproductive growth. Overall, our findings revealed that CsDREB28 inhibits freezing resistance and plant growth by directly transcriptionally inhibiting CsSWEET15/17 to mediate sugar transport and distribution in tea plants.