Abstract

Phytochelatin synthases (PCSs) play essential roles in detoxification of a broad range of heavy metals in plants and other organisms. Until now, however, no PCS gene from liverworts, the earliest branch of land plants and possibly the first one to acquire a PCS with a C-terminal domain, has been characterized. In this study, we isolated and functionally characterized the first PCS gene from a liverwort, Marchantia polymorpha (MpPCS). MpPCS is constitutively expressed in all organs examined, with stronger expression in thallus midrib. The gene expression is repressed by Cd²⁺ and Zn²⁺. The ability of MpPCS to increase heavy metal resistance in yeast and to complement cad1-3 (the null mutant of the Arabidopsis ortholog AtPCS1) proves its function as the only PCS from M. polymorpha. Site-directed mutagenesis of the most conserved cysteines of the C-terminus of the enzyme further uncovered that two twin-cysteine motifs repress, to different extents, enzyme activation by heavy metal exposure. These results highlight an ancestral function of the PCS elusive C-terminus as a regulatory domain inhibiting enzyme overactivation by essential and non-essential heavy metals. The latter finding may be relevant for obtaining crops with decreased root to shoot mobility of cadmium, thus preventing its accumulation in the food chain.

中文翻译：

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植物螯合蛋白合酶C末端结构域在抑制重金属介导的酶过度活化中的祖先功能。

摘要

植物螯合酶合酶（PCS）在植物和其他生物中多种重金属的解毒中起着重要作用。但是至今为止，没有PCS从苔类植物基因，陆生植物的最早分支，并可能以获取与C端结构域的PCS的第一个，已经被表征。在这项研究中，我们分离和功能，其特征在于所述第一PCS从地钱，基因地钱（MpPCS）。MpPCS在所有检查的器官中组成性表达，在th中肋骨中表达更强。Cd ²⁺和Zn ²⁺抑制基因表达。MpPCS的能力增加酵母中重金属的抗性并补充cad1-3（拟南芥直系同源基因AtPCS1的空突变体）证明其作为多形酵母的唯一PCS的功能。酶C端最保守的半胱氨酸的定点诱变进一步发现，两个双半胱氨酸基序在不同程度上抑制了重金属暴露对酶的激活。这些结果突出了PCS难以捉摸的C末端的祖先功能，它是一种调节域，可抑制必需和非必需重金属引起的酶过度活化。后一发现可能与获得镉的根到茎流动性降低的作物有关，从而阻止了镉在食物链中的积累。