5-Aminolevulinic acid (ALA), is a novel plant growth regulator that can enhance plant tolerance against salt stress. However, the molecular mechanism of ALA is not well studied. In this study, ALA improved salt tolerance of apple (Malus × domestica 'Gala') when the detached leaves or cultured calli were used as the materials. The expression of MdWRKY71, a WRKY transcription factor (TF) gene was found to be responsive to NaCl as well as ALA treatment. Functional analysis showed that overexpressing (OE)-MdWRKY71 significantly improved the salt tolerance of the transgenic apple, while RNA interfering (RNAi)-MdWRKY71 reduced the salt tolerance. However, exogenous ALA alleviated the salt damage in the RNAi-MdWRKY71 apple. When MdWRKY71 was transferred into tobacco, the salt tolerance of transgenic plants was enhanced, which was further improved by exogenous ALA. Subsequently, MdWRKY71 bound to the W-box of promoters of MdSOS2, MdNHX1, MdCLC-g, MdSOD1, MdCAT1 and MdAPX1, transcriptionally activating the gene expressions. Since the genes are responsible for Na+ and Cl− transport and antioxidant enzyme activity respectively, it can be concluded that MdWRKY71, a new TF, is involved in ALA-improved salt tolerance by regulating ion homeostasis and redox homeostasis. These results provided new insights into the transcriptional regulatory mechanism of ALA in enhancing apple salt tolerance.

中文翻译：

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MdWRKY71作为正调节剂参与5-氨基乙酰丙酸诱导的苹果耐盐性


5-氨基乙酰丙酸（ALA）是一种新型植物生长调节剂，可以增强植物对盐胁迫的耐受性。然而，ALA的分子机制尚未得到充分研究。在本研究中，以离体叶或培养的愈伤组织为材料时，ALA 提高了苹果（Malus × Domestica 'Gala'）的耐盐性。发现 MdWRKY71（一种 WRKY 转录因子 (TF) 基因）的表达对 NaCl 和 ALA 处理有反应。功能分析表明，过表达（OE）-MdWRKY71显着提高了转基因苹果的耐盐性，而RNA干扰（RNAi）-MdWRKY71降低了转基因苹果的耐盐性。然而，外源ALA减轻了RNAi-MdWRKY71苹果的盐害。当MdWRKY71转入烟草时，转基因植物的耐盐性得到增强，外源ALA进一步提高了这种耐盐性。随后，MdWRKY71 与 MdSOS2、MdNHX1、MdCLC-g、MdSOD1、MdCAT1 和 MdAPX1 启动子的 W 盒结合，转录激活基因表达。由于这些基因分别负责 Na+ 和 Cl− 转运以及抗氧化酶活性，因此可以得出结论，MdWRKY71（一种新的转录因子）通过调节离子稳态和氧化还原稳态参与 ALA 改善的耐盐性。这些结果为ALA增强苹果耐盐性的转录调控机制提供了新的见解。