It has been reported that nitric oxide (NO) could ameliorate cadmium (Cd) toxicity in tall fescue; however, the underlying mechanisms of NO mediated Cd detoxification are largely unknown. In this study, we investigated the possible molecular mechanisms of Cd detoxification process by comparative transcriptomic and metabolomic approaches. The application of Sodium nitroprusside (SNP) as NO donor decreased the Cd content of tall fescue by 11% under Cd stress (T1 treatment), but the Cd content was increased by 24% when treated with Carboxy-PTIO (c-PTIO) together with Nitro-L-arginine methyl ester (L-NAME) (T2 treatment). RNA-seq analysis revealed that 904 (414 up- and 490 down-regulated) and 118 (74 up- and 44 down-regulated) DEGs were identified in the T1 vs Cd (only Cd treatment) and T2 vs Cd comparisons, respectively. Moreover, metabolite profile analysis showed that 99 (65 up- and 34-down- regulated) and 131 (45 up- and 86 down-regulated) metabolites were altered in the T1 vs Cd and T2 vs Cd comparisons, respectively. The integrated analyses of transcriptomic and metabolic data showed that 81 DEGs and 15 differentially expressed metabolites were involved in 20 NO-induced pathways. The dominant pathways were antioxidant activities such as glutathione metabolism, arginine and proline metabolism, secondary metabolites such as flavone and flavonol biosynthesis and phenylpropanoid biosynthesis, ABC transporters, and nitrogen metabolism. In general, the results revealed that there are three major mechanisms involved in NO-mediated Cd detoxification in tall fescue, including (a) antioxidant capacity enhancement; (b) accumulation of secondary metabolites related to cadmium chelation and sequestration; and (c) regulation of cadmium ion transportation, such as ABC transporter activation. In conclusion, this study provides new insights into the NO-mediated cadmium stress response.

中文翻译：

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比较转录组结合代谢组学分析揭示了高羊茅中一氧化氮（NO）调节镉胁迫适应性的关键因素。

据报道，一氧化氮（NO）可以减轻高羊茅中镉（Cd）的毒性。但是，NO介导的Cd排毒的潜在机制尚不清楚。在这项研究中，我们通过比较转录组学和代谢组学方法研究了Cd解毒过程的可能分子机制。硝普钠（SNP）作为NO供体的应用在Cd胁迫下（T1处理）将高羊茅的Cd含量降低了11％，但与Carboxy-PTIO（c-PTIO）一起处理时，Cd含量增加了24％用硝基-L-精氨酸甲酯（L-NAME）（T2处理）。RNA-seq分析显示，在T1与Cd（仅Cd处理）和T2与Cd比较中分别确定了904（上调414和490下调）和118（上调74和44下调）DEG。此外，代谢物谱分析表明，在T1与Cd比较和T2与Cd比较中，分别改变了99种（上调65种，下调34种）和131种（上调45种上调以及86种）。转录组和代谢数据的综合分析表明，81种DEG和15种差异表达的代谢物参与了20种NO诱导的途径。主要途径是谷胱甘肽代谢，精氨酸和脯氨酸代谢等抗氧化剂活性，黄酮和黄酮生物合成和苯丙烷生物合成，ABC转运蛋白和氮代谢等次生代谢产物。总体而言，结果表明，高羊茅中NO介导的Cd排毒涉及三个主要机理，包括：（a）抗氧化能力增强；（b）与镉螯合和螯合有关的次生代谢产物的积累；（c）调节镉离子的运输，例如ABC转运蛋白的活化。总之，这项研究为NO介导的镉胁迫反应提供了新的见解。