Melatonin suppresses ethylene biosynthesis by inhibiting transcription factor MdREM10 during apple fruit ripening

Ethylene, a plant hormone, is essential for apple (Malus domestica) ripening. The precise molecular mechanism by which melatonin (MT) influences ethylene biosynthesis during apple fruit ripening remains unclear. This study found that exogenous MT treatment inhibited ethylene production and postponed apple fruit ripening. The endogenous MT content of apple fruits exhibited an inverse correlation with ethylene production during fruit ripening, suggesting that MT functions as a ripening suppressor in apple fruits. MT treatment suppressed the expression of key ethylene biosynthesis genes, MdACS1 and MdACO1, during apple fruit ripening. MT treatment decreased the expression levels of transcription factors MdREM10 and MdZF32. MdREM10 binds to the MdERF3 promoter, enhancing its expression and subsequently promoting MdACS1 transcription. Furthermore, MdREM10 directly bound to the MdZF32 promoter, promoting its transcription. MdZF32 directly bound to the MdACO1 promoter, inducing its expression. The findings suggested that MT suppresses ethylene biosynthesis and fruit ripening by inhibiting MdREM10, which indirectly promotes MdACS1 transcription via MdERF3 upregulation, and MdACO1 transcription via MdZF32 upregulation.