Li Ling, Yan Xuyu, Li Juan, Wu Xiang, Wang Xiukang
Shaanxi Key Laboratory of Chinese Jujube, College of Life Sciences, Yan'an University, Yan'an, China.
Front Plant Sci. 2022 Sep 20;13:995205. doi: 10.3389/fpls.2022.995205. eCollection 2022.
Cadmium (Cd), a non-essential element for plant, is a ubiquitous and highly toxic heavy metal, seriously endangering agricultural production and human health. As a nonedible economic crop, cotton ( L.) has great potential in remediation of Cd contaminated soil, but its underlying mechanism is still unknown. Melatonin (MT), as a plant growth regulator, is involved in alleviating Cd toxicity in some plants, but the molecular mechanisms of MT-mediated Cd detoxification in cotton are largely unknown. This study investigated the possible molecular mechanisms of the MT-mediated Cd detoxification in cotton seedlings by comparative transcriptomic and metabolomic analyses. The results showed that the cotton seedlings were dwarfed and the leaves were wilted and yellow under Cd stress. The application of 50 mol L MT significantly increased the superoxide dismutase (SOD) activity and malondialdehyde (MDA) content under Cd stress, but 100 mol L MT significantly decreased SOD activity, while increased ascorbate peroxidase (APX) activity significantly. The addition of 100 mol L MT significantly increased Cd concentration in the shoots and roots under Cd stress. RNA-seq analysis showed that 5573, 7105, 7253, 25, 198, 9 up-regulated and 6644, 7192, 7404, 9, 59, 0 down-regulated differentially expressed genes (DEGs) were identified in the comparisons of CK vs T1, CK vs T2, CK vs T3, T1 vs T2, T1 vs T3 and T2 vs T3, respectively. It was revealed that MT promoted the expression of certain related genes under Cd stress, and the effect of 100 mol L MT was better. Moreover, UPLC-MS/MS widely targeted metabolites analyses showed that 195, 150, 150, 12, 24, 59 up-regulated and 16, 11, 23, 38, 127, 66 down-regulated differentially accumulated metabolites (DAMs) were changed in the CK vs T1, CK vs T2, CK vs T3, T1 vs T2, T1 vs T3 and T2 vs T3, respectively. It was revealed that MT induced the synthesis of alkaloids and flavonoids, and inhibited or reduced the synthesis of lipids, amino acids and their derivatives. The comprehensive analyses of transcriptomic and metabolic data showed that 33 DEGs and 4 DAMs, 46 DEGs and 16 DAMs, and 1 DEGs and 1 DAMs were dominantly involved in the pathways of valine, leucine and isoleucine degradation, ABC transporter, alpha-linolenic acid metabolism, respectively. It was revealed that there were three major mechanisms involved in MT-mediated Cd detoxification in cotton, including the enhancement of antioxidant capacity regulated by APX, flavonoids and alkaloids; accumulation of secondary metabolites related to Cd chelation, such as amino acids and derivatives; and regulation of cadmium ion transportation, such as ABC transporter activation. In conclusion, this study provides new insights into the MT-mediated Cd stress response.
镉（Cd）是一种对植物而言非必需的元素，是一种普遍存在且毒性极强的重金属，严重危及农业生产和人类健康。棉花（Gossypium hirsutum L.）作为一种非食用经济作物，在修复镉污染土壤方面具有巨大潜力，但其潜在机制仍不清楚。褪黑素（MT）作为一种植物生长调节剂，参与缓解某些植物中的镉毒性，但MT介导棉花镉解毒的分子机制在很大程度上尚不清楚。本研究通过比较转录组学和代谢组学分析，探究了MT介导棉花幼苗镉解毒的可能分子机制。结果表明，镉胁迫下棉花幼苗矮小，叶片萎蔫发黄。施加50 μmol L⁻¹ MT显著提高了镉胁迫下的超氧化物歧化酶（SOD）活性和丙二醛（MDA）含量，但100 μmol L⁻¹ MT显著降低了SOD活性，同时显著提高了抗坏血酸过氧化物酶（APX）活性。施加100 μmol L⁻¹ MT显著提高了镉胁迫下地上部和根部的镉浓度。RNA测序分析表明，在CK vs T1、CK vs T2、CK vs T3、T1 vs T2、T1 vs T3和T2 vs T3的比较中，分别鉴定出5573、7105、7253、25、198、9个上调和6644、7192、7404、9、59、0个下调的差异表达基因（DEG）。结果表明，MT促进了镉胁迫下某些相关基因的表达，100 μmol L⁻¹ MT的效果更好。此外，超高效液相色谱-串联质谱（UPLC-MS/MS）广泛靶向代谢物分析表明，在CK vs T1、CK vs T2、CK vs T3、T1 vs T2、T1 vs T3和T2 vs T3中，分别有195、150、150,、12、24、59个上调和16、11、23、38、127、66个下调的差异积累代谢物（DAM）发生了变化。结果表明，MT诱导了生物碱和黄酮类化合物的合成，并抑制或减少了脂质、氨基酸及其衍生物的合成。转录组和代谢数据的综合分析表明，分别有33个DEG和4个DAM、46个DEG和16个DAM以及1个DEG和1个DAM主要参与缬氨酸-亮氨酸-异亮氨酸降解、ABC转运蛋白、α-亚麻酸代谢途径。结果表明，MT介导棉花镉解毒主要涉及三种机制，包括由APX、黄酮类化合物和生物碱调节的抗氧化能力增强；与镉螯合相关的次生代谢物积累，如氨基酸及其衍生物；以及镉离子运输调节，如ABC转运蛋白激活。总之，本研究为MT介导的镉胁迫响应提供了新的见解。
