Understanding the molecular mechanisms of cadmium (Cd) tolerance and accumulation in plants is important to address Cd pollution. In the present study, we performed comparative transcriptome analysis to identify the Cd response processes in the roots of two turnip landraces, KTRG-B14 (high-Cd accumulation) and KTRG-B36 (low-Cd accumulation). Two common enhanced processes, glutathione metabolism and antioxidant system, were identified in both landraces. However, some differential antioxidant processes are likely employed by two landraces, namely, several genes encoding peptide methionine sulfoxide reductases and thioredoxins were up-regulated in B14, whereas flavonoid synthesis was potentially induced to fight against oxidative stress in B36. In addition to the commonly upregulated ZINC INDUCED FACILITATOR 1-like gene in two landraces, different metal transporter-encoding genes identified in B14 (DETOXIFICATION 1) and B36 (PLANT CADMIUM RESISTANCE 2-like, probable zinc transporter 10, and ABC transporter C family member 3) were responsible for Cd accumulation and distribution in cells. Several genes that encode extensins were specifically upregulated in B14, which may improve Cd accumulation in cell walls or regulate root development to absorb more Cd. Meanwhile, the induced high-affinity nitrate transporter 2.1-like gene was also likely to contribute to the higher Cd accumulation in B14. However, Cd also caused some toxic symptoms in both landraces. Cd stress might inhibit iron uptake in both landraces whereas many apoenzyme-encoding genes were influenced in B36, which may be attributed to the interaction between Cd and other metal ions. This study provides novel insights into the molecular mechanism of plant root response to Cd at an early stage. The transporters and key enzymes identified in this study are helpful for the molecular-assisted breeding of low- or high-Cd-accumulating plant resources.

了解植物中镉 (Cd) 耐受和积累的分子机制对于解决 Cd 污染很重要。在本研究中，我们进行了比较转录组分析，以确定两种萝卜地方品种 KTRG-B14（高 Cd 积累）和 KTRG-B36（低 Cd 积累）根部的 Cd 响应过程。在两种地方品种中都发现了两种常见的增强过程，即谷胱甘肽代谢和抗氧化系统。然而，两种地方品种可能采用了一些不同的抗氧化过程，即编码肽甲硫氨酸亚砜还原酶和硫氧还蛋白的几个基因在 B14 中上调，而类黄酮合成可能被诱导以对抗 B36 中的氧化应激。除了通常上调的锌诱导促进剂 1 样两种地方品种中的基因，在 B14（解毒 1）和 B36（植物镉抗性2 样，可能的锌转运蛋白 10和ABC 转运蛋白 C 家族成员 3）中鉴定的不同金属转运蛋白编码基因负责细胞中 Cd 的积累和分布. 几个编码延伸蛋白的基因在 B14 中被特异性上调，这可能会改善细胞壁中 Cd 的积累或调节根发育以吸收更多的 Cd。同时，诱导的高亲和力硝酸盐转运蛋白 2.1 样基因也可能有助于 B14 中更高的 Cd 积累。然而，镉也在两种地方品种中引起了一些中毒症状。镉胁迫可能抑制两种地方品种的铁吸收，而许多脱辅基酶编码基因在 B36 中受到影响，这可能归因于镉与其他金属离子之间的相互作用。这项研究为植物根系对早期镉响应的分子机制提供了新的见解。本研究鉴定的转运蛋白和关键酶有助于低或高富集植物资源的分子辅助育种。