Abstract：
Apple (Malus domestica Borkh.) is among the most widely planted and economically valuable horticultural crops globally. Over time, the apple fruit\'s cut surface undergoes browning, and the degree of browning varies among different apple varieties. Browning not only affects the appearance of fruits but also adversely affects their taste and flavor. In the present study, we observed browning in different apple varieties over time and analyzed the expression of genes in the polyphenol oxidase gene family. The results indicated a strong correlation between the browning degree of the fruit and the relative expression of the polyphenol oxidase gene MdPPO2. With the MdPPO2 promoter as bait, the basic leucine zipper (bZIP) transcription factor MdbZIP44 was identified using the yeast single-hybrid screening method. Further investigation revealed that the overexpression of MdbZIP44 in \'Orin\' callus could enhance the expression of MdPPO2 and promote browning of the callus. However, knocking out MdbZIP44 resulted in a callus with no apparent browning phenotype. In addition, our results confirmed the interaction between MdbZIP44 and MdbZIP11. In conclusion, the results indicated that MdbZIP44 can induce apple fruit browning by activating the MdPPO2 promoter. The results provide a theoretical basis for further clarifying the browning mechanism of apple fruit.
摘要：
苹果（MalusdomesticaBorkh。)是全球种植最广泛、最具经济价值的园艺作物之一。随着时间的推移,苹果果实的切面经历褐变，不同苹果品种的褐变程度不同。褐变不仅影响水果的外观,而且不利地影响它们的味道和风味。在本研究中,我们观察了不同苹果品种随时间的褐变，并分析了多酚氧化酶基因家族中基因的表达。结果表明，果实的褐变程度与多酚氧化酶基因MdPPO2的相对表达之间存在很强的相关性。以MdPPO2启动子为诱饵,碱性亮氨酸拉链(bZIP)转录因子MdbZIP44利用酵母单杂交筛选方法进行鉴定。进一步的研究表明，在Orin愈伤组织中MdbZIP44的过表达可以增强MdPPO2的表达并促进愈伤组织的褐变。然而,敲除MdbZIP44导致愈伤组织没有明显的褐变表型。此外,我们的结果证实了MdbZIP44和MdbZIP11之间的相互作用。总之,结果表明，MdbZIP44可以通过激活MdPPO2启动子诱导苹果果实褐变。研究结果为进一步阐明苹果果实褐变机理提供了理论依据。
