An Antagonistic MdERF4–MdERF106 Switch Activates a MdWRKY33 Positive‐Feedback Circuit to Drive Irreversible Ethylene‐Induced Fruit Softening in Apple

Fruit softening represents a defining physiological transition of climacteric fruit ripening, yet the transcriptional mechanisms converting ethylene signalling into an irreversible developmental programme remain largely unresolved. In this study, we identify MdWRKY33 as a central hub linking ethylene signalling to cell wall remodelling during apple fruit softening. MdWRKY33 directly activates the cell wall-degrading enzyme gene MdPG, positively regulates its own transcription, and promotes ethylene production, thereby establishing a self-reinforcing regulatory circuit. Upstream of MdWRKY33, two ethylene-responsive transcription factors, MdERF4 and MdERF106, function antagonistically as a transcriptional repressor and activator, respectively. Ethylene coordinates this regulatory switch by suppressing MdERF4 while inducing MdERF106, thereby sustaining MdWRKY33 transcriptional activation and promoting rapid softening. Our findings reveal that an antagonistic ERF module is coupled with WRKY-mediated positive feedback to establish a robust transcriptional network that reinforces ethylene responses and drives irreversible commitment to the softening programme, providing mechanistic insights and potential targets for fruit quality improvement.