Fresh-cut fruit browning severely affects the appearance of fruit. Light treatment can effectively inhibit fresh-cut apple fruit browning, but the regulatory mechanism remains unknown. Here, we discovered that violet LED light treatment significantly reduced fresh-cut apple fruit browning. Metabolomic analysis revealed that violet LED light treatment enhanced the phenolic accumulation of fresh-cut apple fruit. Transcriptomic analysis showed that the expression of phenolic degradation genes POLYPHENOL OXIDASE (MdPPO) and PEROXIDASE (MdPOD) was reduced, and the expression of phenolic synthesis gene PHENYLALANINE AMMONIA LYASE (MdPAL) was activated by violet LED light treatment. Moreover, two ELONGATED HYPOCOTYL 5 (MdHY5 and MdHYH) transcription factors involved in light signaling were identified. The expression of MdHY5 and MdHYH was activated by violet LED light treatment. Violet LED light treatment no longer inhibited fresh-cut apple fruit browning in MdHY5 or MdHYH silenced fruit. Further experiments revealed that MdHY5 and MdHYH suppressed MdPPO and MdPOD expression and promoted MdPAL expression by binding to their promoters. In addition, MdHY5 and MdHYH bound to each other’s promoters and enhanced their expression. Overall, our findings revealed that violet LED light-activated MdHY5 and MdHYH formed a positive transcriptional loop to regulate the transcription of MdPPO, MdPOD, and MdPAL, which in turn inhibiting the degradation of phenolics and promoting the synthesis of phenolics, thus inhibiting fresh-cut apple fruit browning. These results provide a theoretical basis for improving the appearance and quality of fresh-cut apple fruit.

中文翻译：

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紫光LED光激活MdHY5正向调节酚类积累抑制鲜切苹果果实褐变


鲜切水果褐变严重影响水果的外观。光处理能有效抑制鲜切苹果果实褐变，但其调控机制尚不清楚。在这里，我们发现紫光 LED 光处理显着减少了鲜切苹果果实的褐变。代谢组学分析表明，紫光 LED 光处理增强了鲜切苹果果实中酚类物质的积累。转录组分析表明，紫光LED光处理后，酚类降解基因多酚氧化酶（MdPPO）和过氧化物酶（MdPOD）的表达降低，酚类合成基因苯丙氨酸解氨酶（MdPAL）的表达被激活。此外，还鉴定出了参与光信号传导的两个伸长下胚轴 5（MdHY5 和 MdHYH）转录因子。 MdHY5 和 MdHYH 的表达被紫光 LED 光处理激活。在 MdHY5 或 MdHYH 沉默的果实中，紫光 LED 光处理不再抑制鲜切苹果果实褐变。进一步的实验表明，MdHY5和MdHYH通过与其启动子结合抑制MdPPO和MdPOD表达并促进MdPAL表达。此外，MdHY5和MdHYH与彼此的启动子结合并增强了它们的表达。总体而言，我们的研究结果表明，紫光LED光激活的MdHY5和MdHYH形成正转录环，调节MdPPO、MdPOD和MdPAL的转录，进而抑制酚类物质的降解并促进酚类物质的合成，从而抑制新鲜-切苹果果实褐变。研究结果为改善鲜切苹果外观和品质提供了理论依据。