The process of cadmium (Cd) accumulation and detoxification under different sulfur levels remains largely unknown in woody plants. To investigate the physiological and transcriptomic regulation mechanisms of poplars in response to different sulfate (S) supply levels and Cd exposure, we exposed Populus deltoides saplings to one of the low, moderate and high S levels together with either 0 or 50 µM Cd. Cd accumulation was decreased in low S-treated poplar leaves, and it tended to be increased in high S-supplied leaves under the Cd exposure condition. Sulfur nutrition was deficient in low S-supplied poplars, and it was improved in high S-treated leaves. Cd exposure resulted in lower sulfur level in the leaves supplied with moderate S, it exacerbated a Cd-induced sulfur decrease in low S-treated leaves and it caused a higher sulfur concentration in high S-supplied leaves. In line with the physiological changes, a number of mRNAs and microRNAs (miRNAs) involved in Cd accumulation and sulfur assimilation were identified and the miRNA–mRNA networks were dissected. In the networks, miR395 and miR399 members were identified as hub miRNAs and their targets were ATP sulfurylase 3 (ATPS3) and phosphate 2 (PHO2), respectively. These results suggest that Cd accumulation and sulfur assimilation are constrained by low and enhanced by high S supply, and Cd toxicity is aggravated by low and relieved by high S in poplar leaves, and that miRNA–mRNA regulatory networks play pivotal roles in sulfur-mediated Cd accumulation and detoxification in Cd-exposed poplars.

中文翻译：

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解剖在杨树叶中硫同化和镉积累的MicroRNA-mRNA调控网络。

在木本植物中，在不同硫水平下镉（Cd）的积累和排毒过程仍然未知。为了研究杨树对不同硫酸盐（S）供应水平和Cd暴露的响应的生理和转录组调控机制，我们暴露了Populus deltoides幼树到低，中和高S水平之一，以及0或50 µM Cd。在低S处理的杨树叶片中Cd积累减少，而在Cd暴露条件下，高S供应的叶片中Cd积累倾向于增加。低硫供应的杨树中硫营养不足，高硫处理的叶片中硫营养得到改善。镉暴露导致中度硫供应的叶片中硫含量降低，低硫处理的叶片加剧了镉诱导的硫减少，高硫供应的叶片中硫含量升高。根据生理变化，鉴定了许多与Cd积累和硫同化有关的mRNA和microRNA（miRNA），并解剖了miRNA-mRNA网络。在网络中，miR395和miR399成员被鉴定为集线器miRNA，其靶标为ATP硫化酶3（ATPS3）和磷酸盐2（PHO2）。这些结果表明，杨树叶片中的Cd积累和硫同化受到低硫的限制，而高S供给会增强Cd的毒性，而高S的低硫会减轻Cd的毒性，而miRNA–mRNA调控网络在硫介导的过程中起关键作用。暴露于镉的杨树中镉的积累和排毒。