Abstract Dopamine mediates numerous physiological processes in plants. Tyrosine decarboxylase (TyDC, EC 4.1.1.28) is a common enzyme prevalent in plants and mediates numerous secondary reactions, but little is known about the role of TyDC in the dopamine derivative biosynthesis and function in salt tolerance. Here, apple and apple calli were utilized to study the function of MdTyDC under salt conditions. Overexpression of MdTyDC (OE) significantly increased dopamine content in apple and apple calli. The OE apple lines exhibited increased growth performance and higher photosynthetic capacity and contained more photosynthetic pigments than those of the wild-type lines (WT) under salt conditions. The OE lines had lower H2O2 and O2.− according to DAB and NBT-staining compared to the WT lines. Overexpressing MdTyDC enhanced antioxidant enzyme activities and maintained ion homeostasis, as well as increased the expression levels of associated genes. Furthermore, overexpressing MdTyDC enhanced proline content, increased fresh weight, and reduced malondialdehyde (MDA) content in apple calli; however, RNA interference lines showed higher MDA content and lower fresh weight and proline content. Our findings demonstrate that overexpressing MdTyDC induced higher dopamine levels and increased scavenging of reactive oxygen species and the Na+/K+ balance; thus, enhancing salt tolerance.

中文翻译：

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酪氨酸脱羧酶基因 MdTyDC 的过表达赋予苹果耐盐性

摘要 多巴胺介导植物中的许多生理过程。酪氨酸脱羧酶 (TyDC, EC 4.1.1.28) 是植物中普遍存在的一种常见酶，可介导许多次级反应，但对 TyDC 在多巴胺衍生物生物合成中的作用和耐盐功能知之甚少。在这里，利用苹果和苹果愈伤组织来研究盐条件下 MdTyDC 的功能。MdTyDC (OE) 的过表达显着增加了苹果和苹果愈伤组织中的多巴胺含量。在盐条件下，OE 苹果品系表现出更高的生长性能和更高的光合能力，并且比野生型品系 (WT) 含有更多的光合色素。根据 DAB 和 NBT 染色，与 WT 线相比，OE 线具有较低的 H2O2 和 O2.-。过表达 MdTyDC 可增强抗氧化酶活性并维持离子稳态，并增加相关基因的表达水平。此外，过表达 MdTyDC 可提高苹果愈伤组织中脯氨酸含量、增加鲜重并降低丙二醛 (MDA) 含量；然而，RNA 干扰系显示出较高的 MDA 含量和较低的鲜重和脯氨酸含量。我们的研究结果表明，过表达 MdTyDC 会诱导更高的多巴胺水平，并增加活性氧的清除和 Na+/K+ 平衡；从而提高耐盐性。RNA 干扰系显示较高的 MDA 含量和较低的鲜重和脯氨酸含量。我们的研究结果表明，过表达 MdTyDC 会诱导更高的多巴胺水平，并增加活性氧的清除和 Na+/K+ 平衡；从而提高耐盐性。RNA 干扰系显示较高的 MDA 含量和较低的鲜重和脯氨酸含量。我们的研究结果表明，过表达 MdTyDC 会诱导更高的多巴胺水平，并增加活性氧的清除和 Na+/K+ 平衡；从而提高耐盐性。