College of Horticulture Sciences and Engineering, Shandong Agricultural University, 271018, Tai'an, Shandong, China.
Tai'an Academy of Agricultural Sciences, 271000, Tai'an, Shandong, China.
Plant Physiol Biochem. 2024 Sep;214:108934. doi: 10.1016/j.plaphy.2024.108934. Epub 2024 Jul 13.
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.
苹果（Malus domestica Borkh.）是全球种植最广泛、经济价值最高的园艺作物之一。随着时间的推移，苹果果实的切面会发生褐变，不同品种的苹果褐变程度也不同。褐变不仅影响果实的外观，还会对其口感和风味产生不利影响。在本研究中，我们观察了不同苹果品种随时间的褐变情况，并分析了多酚氧化酶基因家族中基因的表达。结果表明，果实褐变程度与多酚氧化酶基因 MdPPO2 的相对表达呈强相关。利用 MdPPO2 启动子作为诱饵，采用酵母单杂交筛选方法鉴定了基本亮氨酸拉链（bZIP）转录因子 MdbZIP44。进一步研究表明，在 'Orin' 愈伤组织中过表达 MdbZIP44 可以增强 MdPPO2 的表达并促进愈伤组织褐变。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 与 MdbZIP11 之间的相互作用。综上所述，结果表明 MdbZIP44 可以通过激活 MdPPO2 启动子诱导苹果果实褐变。该结果为进一步阐明苹果果实褐变机制提供了理论依据。
