Salicylic acid (SA) plays a role in the regulation of grafting-induced cold tolerance. However, the molecular mechanism behind it is still unknown. Here, we established that the phenylalanine ammonia-lyase (PAL) pathway-dependent elevate in SA content in grafted cucumber leaves was not only synthesized in the leaves but also transported from the roots under chilling stress. RNAi-CsPAL with low SA content as rootstock reduced SA accumulation in grafted seedling leaves while decreasing rootstock-induced cold tolerance, as evidenced by higher electrolyte leakage (EL), hydrogen peroxide (H2O2), and superoxide anion (O2·−) contents and lower expression of cold-responsive genes (CsICE1, CsDREB1A, CsDREB1B, and CsCOR47), whereas OE-CsPAL with high SA content as rootstock improved the cold tolerance of grafted plants in comparison with the wild type (WT). In addition, CsNPR1 was significantly upregulated in grafted cucumber under chilling stress, with exogenous and endogenous overexpressed SA inducing its transcriptional expression and protein stability, which exhibited higher expression in grafted plants than in self-root plants. While CsNPR1-overexpression (OE-CsNPR1) seedlings as scions were more tolerant to chilling stress than WT seedlings, CsNPR1-suppression (Anti-CsNPR1) seedlings as scions were more vulnerable to chilling stress. Notably, CsNPR1–CsICE1 interactions alleviated ROS accumulation and activated the expression of CsDREB1A, CsDREB1B, CsCOR47, CsCOR15, CsCOR413, and CsKIN1 to enhance SA-mediated chilling tolerance in grafted cucumber. Overall, our findings reveal that SA enhances chilling tolerance in grafted cucumbers via the model of the CsNPR1–CsICE1 transcriptional regulatory cascade.

中文翻译：

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水杨酸通过 CsNPR1-CsICE1 相互作用提高嫁接黄瓜的耐冷性


水杨酸 （SA） 在调节接枝诱导的耐寒性中发挥作用。然而，其背后的分子机制仍然未知。在这里，我们确定了嫁接黄瓜叶片中苯丙氨酸解氨酶 （PAL） 途径中 SA 含量的升高不仅在叶片中合成，而且在寒冷胁迫下从根部运输。作为砧木的 SA 含量低的 RNAi-CsPAL 减少了嫁接幼苗叶片中的 SA 积累，同时降低了砧木诱导的耐寒性，电解质泄漏 （EL）、过氧化氢 （H2O2） 和超氧阴离子 （O2·−） 含量较高，冷响应基因 （CsICE1、CsDREB1A、CsDREB1B 和 CsCOR47） 的表达较低，而与野生型 （WT） 相比，SA 含量高的砧木 OE-CsPAL 提高了嫁接植株的耐寒性。此外，在低温胁迫下，CsNPR1 在嫁接黄瓜中显著上调，外源和内源过表达 SA 诱导其转录表达和蛋白稳定性，在嫁接植株中表达高于自根植株。虽然作为接穗的 CsNPR1 过表达 （OE-CsNPR1） 幼苗比 WT 幼苗更耐低温胁迫，但作为接穗的 CsNPR1 抑制 （抗 CsNPR1） 幼苗更易受到低温胁迫。值得注意的是，CsNPR1-CsICE1 相互作用减轻了 ROS 积累，并激活了 CsDREB1A 、 CsDREB1B 、 CsCOR47 、 CsCOR15 、 CsCOR413 和 CsKIN1 的表达，以增强 SA 介导的嫁接黄瓜的寒冷耐受性。总体而言，我们的研究结果表明，SA 通过 CsNPR1-CsICE1 转录调节级联模型增强了嫁接黄瓜的冷酷耐受性。