Soil alkalization affects apple production in northwest China. Autophagy is a highly conserved degradative protein pathway in eukaryotes. Autophagy in plants can be activated by various abiotic factors. We previously identified the positive role of the autophagy-related gene MdATG18a in drought, nitrogen deficiency and resistance to Diplocarpon mali infection in apple. However, it is still unclear whether ATG18a is related to alkaline stress. In this study, we used hydroponic culture to simulate alkaline stress and found that the overexpression of MdATG18a significantly improved the tolerance of apple to alkaline stress. The overexpression of MdATG18a increased biomass, photosynthetic rate and antioxidant capacity of transgenic plants compared with wild-type plants under alkaline stress. The overexpression of MdATG18a promoted γ-aminobutyric acid (GABA) shunt via an increase in glutamate (GABA precursor) and GABA contents and upregulation of GABA shunt-related genes. In addition, the overexpression of MdATG18a significantly upregulated the expression of other core ATG genes and increased the formation of autophagosomes under alkaline stress. In conclusion, these results suggest that the overexpression of MdATG18a in apple enhances alkaline tolerance and the GABA shunt, which may be owing to the increase in autophagic activity.

中文翻译：

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通过在碱性条件下增加自噬，MdATG18a的过表达增强了苹果的耐碱性和GABA分流。

土壤碱化影响西北地区的苹果生产。自噬是真核生物中高度保守的降解蛋白途径。植物中的自噬可以被各种非生物因子激活。我们以前确定的自噬相关基因的积极作用MdATG18a干旱，缺氮和耐Diplocarpon马里苹果感染。然而，尚不清楚ATG18a是否与碱性胁迫有关。在这项研究中，我们使用水培法模拟碱性胁迫，发现MdATG18a的过表达显着提高了苹果对碱性胁迫的耐受性。MdATG18a的过表达与碱性胁迫下的野生型植物相比，转基因植物的生物量，光合速率和抗氧化能力均有所提高。MdATG18a的过表达通过增加谷氨酸（GABA前体）和GABA含量以及上调GABA分流相关基因来促进γ-氨基丁酸（GABA）分流。此外，MdATG18a的过表达显着上调了其他核心ATG基因的表达，并增加了碱性胁迫下自噬体的形成。总之，这些结果表明苹果中MdATG18a的过表达增强了耐碱性和GABA分流，这可能是由于自噬活性的增加所致。