Color is an important trait for horticultural crops. Carotenoids are one of the main pigments for coloration and have important implications for photosynthesis in plants and benefits for human health. Here, we identified an APETALA2 (AP2)/ETHYLENE RESPONSE FACTOR (ERF) transcription factor named MdAP2-34 in apple (Malus domestica Borkh.). MdAP2-34 expression exhibited a close correlation with carotenoid content in ‘Benin Shogun’ and ‘Yanfu 3’ fruit flesh. MdAP2-34 promotes carotenoid accumulation in MdAP2-34-OVX transgenic apple calli and fruits by participating in the carotenoid biosynthesis pathway. The major carotenoid contents of phytoene and β-carotene were much higher in overexpressing MdAP2-34 transgenic calli and fruit skin, yet the predominant compound of lutein showed no obvious difference, indicating that MdAP2-34 regulates phytoene and β-carotene accumulation but not lutein. MdPSY2-1 (phytoene synthase 2) is a major gene in the carotenoid biosynthesis pathway in apple fruit, and the MdPSY2-1 gene is directly bound and transcriptionally activated by MdAP2-34. In addition, overexpressing MdPSY2-1 in apple calli mainly increases phytoene and total carotenoid contents. Our findings will advance and extend our understanding of the complex molecular mechanisms of carotenoid biosynthesis in apple, and this research is valuable for accelerating the apple breeding process.

中文翻译：

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苹果（Malus domestica）AP2/ERF转录因子调节类胡萝卜素积累

颜色是园艺作物的重要特征。类胡萝卜素是着色的主要色素之一，对植物的光合作用和人类健康具有重要意义。在这里，我们在苹果中鉴定出一种名为 MdAP2-34 的 APETALA2 (AP2)/乙烯反应因子 (ERF) 转录因子。海棠博尔赫。）。MdAP2-34表达与'贝宁将军'和'延福3'果肉中的类胡萝卜素含量密切相关。MdAP2-34 通过参与类胡萝卜素生物合成途径促进 MdAP2-34-OVX 转基因苹果愈伤组织和果实中的类胡萝卜素积累。过表达的MdAP2-34转基因愈伤组织和果皮中八氢番茄红素和β-胡萝卜素的主要类胡萝卜素含量要高得多，而叶黄素的主要成分没有明显差异，表明MdAP2-34调节八氢番茄红素和β-胡萝卜素的积累而不是叶黄素.MdPSY2-1(八氢番茄红素合成酶 2) 是苹果果实类胡萝卜素生物合成途径中的主要基因。MdPSY2-1基因被 MdAP2-34 直接结合和转录激活。此外，过度表达MdPSY2-1苹果愈伤组织中主要增加八氢番茄红素和总类胡萝卜素的含量。我们的研究结果将推进和扩展我们对苹果类胡萝卜素生物合成复杂分子机制的理解，这项研究对于加速苹果育种过程具有重要意义。