SUMOylation is involved in various aspects of plant biology, including drought stress. However, the relationship between SUMOylation and drought stress tolerance is complex; whether SUMOylation has a crosstalk with ubiquitination in response to drought stress remains largely unclear. In this study, we found that both increased and decreased SUMOylation led to increased survival of apple (Malus × domestica) under drought stress: both transgenic MdSUMO2A overexpressing (OE) plants and MdSUMO2 RNAi plants exhibited enhanced drought tolerance. We further confirmed that MdDREB2A is one of the MdSUMO2 targets. Both transgenic MdDREB2A OE and MdDREB2A^K192R OE plants (which lacked the key site of SUMOylation by MdSUMO2A) were more drought tolerant than wild-type plants. However, MdDREB2A^K192R OE plants had a much higher survival rate than MdDREB2A OE plants. We further showed SUMOylated MdDREB2A was conjugated with ubiquitin by MdRNF4 under drought stress, thereby triggering its protein degradation. In addition, MdRNF4 RNAi plants were more tolerant to drought stress. These results revealed the molecular mechanisms that underlie the relationship of SUMOylation with drought tolerance and provided evidence for the tight control of MdDREB2A accumulation under drought stress mediated by SUMOylation and ubiquitination.

中文翻译：

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SUMOylation的微调调节苹果的耐旱性

SUMOylation 涉及植物生物学的各个方面，包括干旱胁迫。然而，SUMOylation 与干旱胁迫耐受性之间的关系是复杂的。SUMOylation 是否与泛素化反应以应对干旱胁迫在很大程度上仍不清楚。在这项研究中，我们发现增加和减少 SUMOylation 都会导致苹果 ( Malus  ×  domestica ) 在干旱胁迫下的存活率增加：转基因MdSUMO2A过表达 (OE) 植物和MdSUMO2 RNAi 植物都表现出增强的耐旱性。我们进一步证实 MdDREB2A 是 MdSUMO2 的靶标之一。转基因MdDREB2A OE 和MdDREB2A ^K192ROE 植物（缺乏 MdSUMO2A SUMOylation 的关键位点）比野生型植物更耐旱。然而，MdDREB2A ^K192R OE 植物的存活率远高于MdDREB2A OE 植物。我们进一步表明，SUMOylated MdDREB2A 在干旱胁迫下通过 MdRNF4 与泛素结合，从而触发其蛋白质降解。此外，MdRNF4 RNAi 植物对干旱胁迫的耐受性更强。这些结果揭示了 SUMO 化与干旱耐受性关系的分子机制，并为在 SUMO 化和泛素化介导的干旱胁迫下严格控制 MdDREB2A 积累提供了证据。