DataSheet_1_Low-level cadmium exposure induced hormesis in peppermint young plant by constantly activating antioxidant activity based on physiological and transcriptomic analyses.xlsx

As one of the most toxic environmental pollutants, cadmium (Cd) has lastingly been considered to have negative influences on plant growth and productivity. Recently, increasing studies have shown that low level of Cd exposure could induce hormetic effect which benefits to plants. However, the underlying mechanisms of Cd-triggered hormesis are poorly understood. In this study, we found that Cd stress treatment showed a hormetic effect on peppermint and Cd treatment with 1.6 mg L-1 concertation manifested best stimulative effects. To explore the hormesis mechanisms of Cd treatment, comparative transcriptome analysis of peppermint young plants under low (1.6 mg L-1) and high (6.5 mg L-1) level of Cd exposure at 0 h, 24 h and 72 h were conducted. Twelve of differentially expressed genes (DEGs) were selected for qRT-PCR validation, and the expression results confirmed the credibility of transcriptome data. KEGG analysis of DEGs showed that the phenylpropanoid biosynthesis and photosynthesis were important under both low and high level of Cd treatments. Interestingly, GO and KEGG analysis of 99 DEGs specifically induced by low level of Cd treatment at 72 h indicated that these DEGs were mainly involved in the pathway of phenylpropanoid biosynthesis and their functions were associated with antioxidant activity. The expression pattern of those genes in the phenylpropanoid biosynthesis pathway and encoding antioxidant enzymes during 72 h of Cd exposure showed that low level of Cd treatment induced a continuation in the upward trend but high level of Cd treatment caused an inverted V-shape. The changes of physiological parameters during Cd exposure were highly consistent with gene expression pattern. These results strongly demonstrate that low level of Cd exposure constantly enhanced antioxidant activity of peppermint to avoid oxidative damages caused by Cd ion, while high level of Cd stress just induced a temporary increase in antioxidant activity which was insufficient to cope with lasting Cd toxicity. Overall, the results presented in this study shed a light on the underlying mechanisms of the Cd-mediated hormesis in plant. Moreover, our study provided a safe method for the efficient utilization of mild Cd-contaminated soil as peppermint is an important cash plant.

镉（Cd）作为毒性最强的环境污染物之一，长期以来被认为会对植物生长及生产力产生负面影响。近年来，越来越多的研究表明，低浓度镉暴露可诱导对植物有益的兴奋效应（hormetic effect）。然而，镉诱导的兴奋效应的潜在分子机制尚未被充分阐明。
本研究发现，镉胁迫处理对薄荷（peppermint）具有兴奋效应，其中1.6 mg·L⁻¹浓度的镉处理展现出最佳的促生长效果。为解析镉处理诱导兴奋效应的分子机制，本研究对分别经低浓度（1.6 mg·L⁻¹）与高浓度（6.5 mg·L⁻¹）镉暴露0 h、24 h及72 h的薄荷幼苗开展了比较转录组分析。本研究选取12个差异表达基因（differentially expressed genes, DEGs）进行qRT-PCR验证，基因表达结果证实了转录组数据的可靠性。对差异表达基因的KEGG分析显示，苯丙烷类生物合成（phenylpropanoid biosynthesis）与光合作用途径在高低浓度镉处理下均发挥重要作用。有趣的是，对72 h时仅由低浓度镉处理诱导的99个差异表达基因进行基因本体（Gene Ontology, GO）与KEGG分析后发现，这些基因主要参与苯丙烷类生物合成途径，且其功能与抗氧化活性相关。在72 h镉暴露过程中，苯丙烷类生物合成途径及编码抗氧化酶的相关基因的表达模式显示：低浓度镉处理下基因表达呈持续上升趋势，而高浓度镉处理下则呈现倒V型变化。镉暴露过程中生理指标的变化趋势与基因表达模式高度一致。
上述结果充分证实：低浓度镉暴露可持续增强薄荷的抗氧化活性，以抵御镉离子诱导的氧化损伤；而高浓度镉胁迫仅能引发抗氧化活性的短暂升高，不足以应对持续存在的镉毒性。综上，本研究结果阐明了植物中镉介导的兴奋效应的潜在分子机制。此外，由于薄荷是重要的经济作物，本研究为轻度镉污染土壤的高效安全利用提供了可行方案。