Drought is the most severe form of stress experienced by plants worldwide. Cucumber is a vegetable crop that requires a large amount of water throughout the growth period. In our previous study, we identified that overexpression of CsHSFA1d could improve cold tolerance and the content of endogenous jasmonic acid in cucumber seedlings. To explore the functional diversities of CsHSFA1d, we treat the transgenic plants under drought conditions. In this study, we found that the heat shock transcription factor HSFA1d (CsHSFA1d) could improve drought stress tolerance in cucumber. CsHSFA1d overexpression increased the expression levels of galactinol synthase (CsGolS3) and raffinose synthase (CsRS) genes, encoding the key enzymes for raffinose family oligosaccharide (RFO) biosynthesis. Furthermore, the lines overexpressing CsHSFA1d showed higher enzymatic activity of GolS and raffinose synthase to increase the content of RFO. Moreover, the CsHSFA1d-overexpression lines showed lower reactive oxygen species (ROS) accumulation and higher ROS-scavenging enzyme activity after drought treatment. The expressions of antioxidant genes CsPOD2, CsAPX1 and CsSOD1 were also upregulated in CsHSFA1d-overexpression lines. The expression levels of stress-responsive genes such as CsRD29A, CsLEA3 and CsP5CS1 were increased in CsHSFA1d-overexpression lines after drought treatment. We conclude that CsHSFA1d directly targets and regulates the expression of CsGolS3 and CsRS to promote the enzymatic activity and accumulation of RFO to increase the tolerance to drought stress. CsHSFA1d also improves ROS-scavenging enzyme activity and gene expression indirectly to reduce drought-induced ROS overaccumulation. This study therefore offers a new gene target to improve drought stress tolerance in cucumber and revealed the underlying mechanism by which CsHSFA1d functions in the drought stress by increasing the content of RFOs and scavenging the excessive accumulation of ROS.

中文翻译：

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CsHSFA1d通过增加黄瓜中棉子糖家族寡糖的含量和清除积累的活性氧来提高干旱胁迫耐受性

干旱是全世界植物所经历的最严重的胁迫形式。黄瓜是一种蔬菜作物，整个生长期需要大量的水。在我们前期的研究中，我们发现CsHSFA1d的过表达可以提高黄瓜幼苗的耐寒性和内源茉莉酸的含量。为了探索 CsHSFA1d 的功能多样性，我们在干旱条件下处理转基因植物。在本研究中，我们发现热激转录因子HSFA1d（CsHSFA1d）可以提高黄瓜的干旱胁迫耐受性。 CsHSFA1d 过表达增加了半乳糖醇合酶 (CsGolS3) 和棉子糖合酶 (CsRS) 基因的表达水平，这些基因编码棉子糖家族寡糖 (RFO) 生物合成的关键酶。此外，过表达CsHSFA1d的品系表现出更高的GolS和棉子糖合酶活性，从而增加了RFO的含量。此外，CsHSFA1d过表达株系在干旱处理后表现出较低的活性氧（ROS）积累和较高的ROS清除酶活性。在 CsHSFA1d 过表达株系中，抗氧化基因 CsPOD2、CsAPX1 和 CsSOD1 的表达也上调。干旱处理后，CsHSFA1d 过表达株系中 CsRD29A、CsLEA3 和 CsP5CS1 等胁迫响应基因的表达水平增加。我们得出结论，CsHSFA1d直接靶向并调节CsGolS3和CsRS的表达，以促进酶活性和RFO的积累，从而提高对干旱胁迫的耐受性。 CsHSFA1d 还可以间接提高 ROS 清除酶活性和基因表达，以减少干旱引起的 ROS 过度积累。因此，本研究为提高黄瓜的干旱胁迫耐受性提供了一个新的基因靶点，并揭示了CsHSFA1d通过增加RFOs含量和清除过量积累的ROS在干旱胁迫中发挥作用的潜在机制。