Controlling Ascorbic Acid Loss in Kiwifruit: The AcERF61-AcZFP3 Transcription Complex Mediates Postharvest Degradation by Activating AcAO9

Ascorbic acid (AsA) degradation during postharvest storage significantly reduces the nutritional quality of kiwifruit. This study revealed that 1-methylcyclopropene (1-MCP) delayed postharvest softening and ethylene production, and it delayed AsA loss by suppressing ascorbate oxidase (AO) activity. Transcriptomic analysis identified 13 AcAO genes, with AcAO9 expression strongly induced during ripening and inhibited by 1-MCP. Transient overexpression and silencing of AcAO9 confirmed its role in regulating AO activity and AsA content. Furthermore, the zinc finger transcription factor AcZFP3 was shown to directly bind to the AcAO9 promoter and activate its expression. AcZFP3 itself was transcriptionally regulated by AcERF61, which bound to the AcZFP3 promoter. Functional assays demonstrated that both AcZFP3 and AcERF61 positively regulate AO activity and promote AsA degradation. Collectively, our results demonstrate that 1-MCP maintains postharvest AsA levels in kiwifruit via the AcERF61-AcZFP3-AcAO9 module to attenuate AO activity. These findings provide novel insights into the regulation of postharvest AsA metabolism in kiwifruit.