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

Ethylene-induced apple fruit softening is driven by MdWRKY33, which directly activates MdPG and forms a self-reinforcing loop that sustains ethylene production.

• Why it matters: The transcriptional steps that translate ethylene signalling into an irreversible ripening programme in apple fruit are not well defined.
• What they did: The study mapped an ethylene-responsive network in apple, showing MdERF4 and MdERF106 act antagonistically upstream of MdWRKY33, with ethylene suppressing MdERF4 and inducing MdERF106.
• The result: The coupled ERF switch and MdWRKY33 positive-feedback circuit reinforces ethylene responses and promotes rapid, irreversible commitment to the softening programme, suggesting targets to improve fruit quality.

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