CmDREBa regulates the perennial growth habit of chrysanthemum in response to prolonged chilling.

Seasonal growth modulation is a key adaptive trait in perennials that supports overwinter survival. During winter, many perennials adopt a rosette growth habit by suppressing both vegetative extension and flowering, but the mechanism that coordinates these two distinct developmental programs remains unclear. Here, we show that prolonged chilling primarily acts at the shoot apex to confer extension growth and flowering competence in chrysanthemum (Chrysanthemum morifolium). Long-term chilling is accompanied by marked changes in gene expression in the rib zone of the shoot apex. Notably, the expression of CmDREBa is associated with the transition from extension growth to rosette growth. Chilling induces CmDREBa expression, which suppresses both extension growth and flowering; when temperatures rise, CmDREBa expression declines, allowing both processes to resume. CmDREBa directly induces the expression of MADS AFFECTING FLOWERING (MAF) genes, which in turn promote rosette growth. Together, these findings identify CmDREBa as a key regulator of chilling-responsive seasonal growth.