Heavy metals (HMs), in particular the toxic/carcinogenic non-essential ones including cadmium (Cd), arsenic (As), aluminum (Al), mercury (Hg), and lead (Pb) are known to exert severe impacts on plant growth and yields. HM contamination and/or toxicity is seen a major threat for global food production, quality, and security. Plants use intricate molecular mechanisms for responding and adapting to HM stress, both at transcriptional and post-transcriptional levels, and microRNA (miRNA) have emerged as key post-transcriptional regulators. These tiny (19–25 nucleotide) non-coding RNA species found abundantly in plants are pivotal in tight regulation of gene expression via miRNA-directed mRNA cleavage, translational repression, chromatin remodeling, or through epigenetic modification. MiRNAs are reported to be involved in regulation of HM uptake and transport, besides their chelation and homeostasis, as well as in HM-induced oxidative stress and antioxidative defense. There are also reports of involvement of miRNAs in metallic cross- and co-tolerance. Technological advents in small RNA sequencing coupled with computational tools and databases have resulted into the identification, characterization, and validation of several HM-responsive miRNAs along with their respective target genes. Through his review, we present and discuss current understandings on miRNAs, their biosynthesis, and functions in plants, emphasizing on HM stress responses and adaptations. The main aim of this review is to discuss the possible exploration of plant miRNAs as potential targets for engineering plants (via loss-/gain-of-function approaches) to confer HM tolerance. Successful case studies, current challenges, and future directions are also discussed.

重金属 (HMs)，特别是有毒/致癌的非必需元素，包括镉 (Cd)、砷 (As)、铝 (Al)、汞 (Hg) 和铅 (Pb)，已知会对植物产生严重影响增长和产量。HM 污染和/或毒性被视为全球食品生产、质量和安全的主要威胁。植物在转录和转录后水平上使用复杂的分子机制来响应和适应 HM 胁迫，而 microRNA (miRNA) 已成为关键的转录后调节因子。这些在植物中大量发现的微小（19-25 个核苷酸）非编码 RNA 物种在通过 miRNA 指导的 mRNA 切割、翻译抑制、染色质重塑或通过表观遗传修饰严密调控基因表达方面发挥着关键作用。据报道，除了螯合和稳态外，miRNA 还参与 HM 摄取和运输的调节，以及 HM 诱导的氧化应激和抗氧化防御。也有关于 miRNA 参与金属交叉和共耐受的报道。小 RNA 测序技术的出现与计算工具和数据库相结合，已导致对几种 HM 响应 miRNA 及其各自靶基因的识别、表征和验证。通过他的评论，我们展示并讨论了当前对 miRNA、它们的生物合成和植物功能的理解，强调了 HM 应激反应和适应。本综述的主要目的是讨论植物 miRNA 作为工程植物的潜在靶标（通过功能丧失/功能获得方法）以赋予 HM 耐受性的可能性探索。还讨论了成功的案例研究、当前的挑战和未来的方向。