The Ni hyperaccumulator Odontarrhena chalcidica (formerly Alyssum murale), exhibits a significant capacity to accumulate Zn in the roots. However, the molecular mechanisms underlying the variation in Ni and Zn accumulation are poorly understood. Here, we isolated a homolog of heavy metal ATPase 3 from O. chalcidica (OcHMA3) and characterized its functions using heterologous systems. Phylogenetic analysis revealed that OcHMA3 protein shares 87.6 % identity with AtHMA3, with similar metal binding sites to other HMA3 proteins. Heterologous expression of OcHMA3 in yeast increased sensitivity to Cd, Ni and Zn, suggesting it functions as a broad-specificity transporter. Further investigation showed OcHMA3 is constitutively expressed in the roots and localized to the tonoplast. Overexpression of OcHMA3 in A. thaliana shoots increased its roots Zn concentrations by 41.9 % – 74.1 %. However, overexpression of OcHMA3 in roots enhanced its tolerance to Cd and increased roots Cd concentrations by 50.9 % – 90.6 %. Our findings indicated OcHMA3 is responsible for Zn sequestration in root vacuoles, likely leading to Zn retention in roots and subsequent Ni hyperaccumulation in shoots. This study elucidates the molecular mechanism of Ni and Zn accumulation in O. chalcidica, and identifies OcHMA3 as a potential gene for developing Zn-rich plants and for phytoextraction in Cd-contaminated soils.

中文翻译：

---

来自 Odontarrhena chalcidica 的根 Zn 螯合转运蛋白重金属 ATP 酶 3 增强了拟南芥的 Cd 耐受性和积累


Ni 超蓄积器 Odontarrhena chalcidica（以前的 Alyssum murale）表现出在根中积累 Zn 的重要能力。然而，人们对 Ni 和 Zn 积累变化的分子机制知之甚少。在这里，我们从 O. chalcidica （OcHMA3） 中分离出重金属 ATP 酶 3 的同源物，并使用异源系统表征其功能。系统发育分析显示，OcHMA3 蛋白与 AtHMA3 具有 87.6% 的同一性，与其他 HMA3 蛋白具有相似的金属结合位点。酵母中 OcHMA3 的异源表达增加了对 Cd、Ni 和 Zn 的敏感性，表明它起着广泛特异性转运蛋白的作用。进一步研究显示 OcHMA3 在根中组成型表达并定位于软质体。拟南芥芽中过表达 OcHMA3 使其根系 Zn 浓度增加了 41.9 % – 74.1 %。然而，OcHMA3 在根中的过表达增强了其对 Cd 的耐受性，并使根 Cd 浓度增加了 50.9 % – 90.6 %。我们的研究结果表明，OcHMA3 负责根液泡中的 Zn 封存，可能导致 Zn 在根中的滞留和随后的 Ni 在芽中过度积累。本研究阐明了 O. chalcidica 中 Ni 和 Zn 积累的分子机制，并确定 OcHMA3 是发育富锌植物和在 Cd 污染土壤中植物提取的潜在基因。