Miniature inverted-repeat transposable elements (MITEs) are widely distributed in the plant genome and can be methylated. However, whether DNA methylation of MITEs is associated with induced allelic expression and drought tolerance is unclear. Here, we identified the drought-inducible MdRFNR1 (root-type ferredoxin-NADP+ oxidoreductase) gene in apple (Malus domestica). MdRFNR1 plays a positive role in drought tolerance by regulating the redox system, including increasing NADP+ accumulation and catalase and peroxidase activities and decreasing NADPH levels. Sequence analysis identified a MITE insertion (MITE-MdRF1) in the promoter of MdRFNR1-1 but not the MdRFNR1-2 allele. MdRFNR1-1 but not MdRFNR1-2 expression was significantly induced by drought stress, which was positively associated with the MITE-MdRF1 insertion and its DNA methylation. The methylated MITE-MdRF1 is recognized by the transcriptional anti-silencing factors MdSUVH1 and MdSUVH3, which recruit the DNAJ domain-containing proteins MdDNAJ1, MdDNAJ2, and MdDNAJ5, thereby activating MdRFNR1-1 expression under drought stress. Finally, we showed that MdSUVH1 and MdDNAJ1 are positive regulators of drought tolerance. These findings illustrate the molecular roles of methylated MITE-MdRF1 (which is recognized by the MdSUVH-MdDNAJ complex) in induced MdRFNR1-1 expression as well as the drought response of apple and shed light on the molecular mechanisms of natural variation in perennial trees.

中文翻译：

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MdRFNR1-1 启动子中 MITE 插入的甲基化与其在苹果中响应干旱胁迫的等位基因表达呈正相关。

微型反向重复转座元件（MITE）广泛分布于植物基因组中，并且可以被甲基化。然而，MITEs 的 DNA 甲基化是否与诱导等位基因表达和耐旱性相关尚不清楚。在这里，我们鉴定了苹果 (Malus Domestica) 中的干旱诱导型 MdRFNR1（根型铁氧还蛋白-NADP+氧化还原酶）基因。MdRFNR1 通过调节氧化还原系统，包括增加 NADP+ 积累、过氧化氢酶和过氧化物酶活性以及降低 NADPH 水平，在耐旱性中发挥积极作用。序列分析发现 MITE 插入 (MITE-MdRF1) 在 MdRFNR1-1 的启动子中，但在 MdRFNR1-2 等位基因中没有。干旱胁迫显着诱导 MdRFNR1-1 表达，但不显着诱导 MdRFNR1-2 表达，这与 MITE-MdRF1 插入及其 DNA 甲基化呈正相关。甲基化的MITE-MdRF1被转录抗沉默因子MdSUVH1和MdSUVH3识别，它们招募含有DNAJ结构域的蛋白MdDNAJ1、MdDNAJ2和MdDNAJ5，从而在干旱胁迫下激活MdRFNR1-1的表达。最后，我们证明 MdSUVH1 和 MdDNAJ1 是耐旱性的正调节因子。这些发现说明了甲基化 MITE-MdRF1（由 MdSUVH-MdDNAJ 复合物识别）在诱导 MdRFNR1-1 表达以及苹果的干旱反应中的分子作用，并揭示了多年生树木自然变异的分子机制。