Chilling-responsive strigolactone signaling orchestrates bud break and chilling tolerance in apple

Temperature is a critical factor governing apple (Malus domestica) cultivation. Adequate chilling exposure promotes bud dormancy release, but prolonged chilling induces crop damage. However, the mechanisms underlying apple adaptation to varying chilling durations remain elusive. Here, we identify strigolactones (SLs) as dual regulators that suppress vegetative bud break while promoting chilling tolerance, with MdD53 (MdDWARF53) serving as the central integrator of these 2 responses. During fulfillment of the chilling requirement (CR), low temperature induces the expression of MdCBF4 (encoding a C-repeat binding transcription factor) and MdTCP14 (encoding a Teosinte branched1/cycloidea/proliferating cell factor). These factors interact and activate MdD53 transcription, thus promoting bud break. As chilling continues, increased SLs accelerate MdD53 degradation to enhance chilling tolerance; before CR fulfillment, MdD53 synthesis predominates (despite rising SLs) to ensure bud break competence. Under excessive chilling, elevated levels of SLs enhance MdD53 degradation and trigger MdMEK5-dependent phosphorylation of MdICE1 (Inducer of CBF Expression 1). This disrupts the MdD53-MdICE1 interaction, releasing MdICE1 to activate MdCBF1/3 expression. This shift prioritizes chilling tolerance over bud break competence, consequently weakening bud break capacity. Collectively, our results delineate the mechanistic basis for how SL-coordinated bud break and chilling tolerance define the latitudinal limits of apple cultivation.