锰(Mn)是植物必需矿质元素, 其缺乏或过量均影响植物生长发育。鉴定植物中介导锰积累的关键基因并揭示其作用机制, 对于作物遗传改良以及锰污染生物修复具有重要意义。从镉(Cd)/锌(Zn)超积累植物伴矿景天( Sedum plumbizincicola)中克隆到1个阳离子扩散促进子(cation diffusion facilitator, CDF)家族成员基因 SpMTP10。其在酵母( Saccharomyces cerevisiae)中表达后能够极大地增强转化子对过量锰胁迫的耐受性, 同时转化子中锰积累增加, 但对镉、锌、铜(Cu)、铁(Fe)等其它金属元素过量胁迫的耐受性以及积累的作用不显著。亚细胞定位分析表明其定位于内质网膜。在拟南芥( Arabidopsis thaliana)中异源表达 SpMTP10使植物根部锰积累减少, 地上部锰积累增多, 且对过量锰胁迫更敏感。研究结果表明, SpMTP10可能通过促进锰向内质网的区隔增强酵母对过量锰毒害的耐受性。而在植物中表达后, SpMTP10介导锰向内质网转运则可能促进了内质网腔中锰通过胞间连丝进行细胞间迁移, 从而促进锰向根部维管组织移动并向茎部转运。

INTRODUCTION: Manganese (Mn) is an essential micronutrient for plant growth and primarily acts as an enzyme cofactor and participates in the redox processes. However, excessive absorption of Mn by plants can also induce toxicity damage. Therefore, plants need to tightly regulate the uptake, homeostasis, and distribution of Mn to cope with stresses caused by its deficiency or excess. In these processes, cation diffusion facilitator (CDF) family transporters, which in plants are also known as metal tolerance proteins (MTPs), have been shown to be crucial for Mn homeostasis. Therefore, identifying MTP family genes and elucidating their underlying mechanisms for Mn accumulation would provide not only novel insights into basic scientific issues of plant Mn accumulation but also gene resources for crop improvement and Mn pollution bioremediation. RATIONALE: Sedum plumbizincicola is a recently discovered Cd/Zn hyperaccumulator that grows in mining areas. The soil in its natural habitat contains more than 10 000 mg·kg^–1 Mn, suggesting that S. plumbizincicola may have efficient Mn transport and detoxification capabilities. Based on the transcriptome sequencing results of S. plumbizincicola obtained previously, a member of the MTP family gene named SpMTP10 was cloned and its role in mediating Mn accumulation was investigated in this study. RESULTS: Phylogenetic analysis with orthologs from Arabidopsis and rice revealed that SpMTP10 belongs to the Mn-CDF subfamily and is most closely related to AtMTP10, AtMTP9 and OsMTP9, with the highest sequence identity of 72% to AtMTP10. SpMTP10 is mainly expressed in the roots of S. plumbizincicola and its expression level is not affected by Mn treatment. Expression of SpMTP10 in yeast can greatly enhance the tolerance of transformants to excessive Mn stress and increase Mn accumulation in transformants. However, under conditions of excessive cadmium (Cd), zinc (Zn), copper (Cu), and iron (Fe) stress, the yeast transformants exhibited no significant changes in tolerance. Subsequent subcellular localization analysis revealed that SpMTP10 was localized to the endoplasmic reticulum (ER) membrane. Compared with wild-type plants, transgenic Arabidopsis overexpressing SpMTP10 demonstrated reduced Mn accumulation in roots but increased Mn accumulation in shoots, rendering the plants more sensitive to excessive Mn stress. CONCLUSION: In conclusion, SpMTP10 likely enhances yeast tolerance to excessive Mn toxicity by promoting Mn sequestration in the ER. In plants, Mn transport mediated by SpMTP10 into the ER may facilitate intercellular migration of Mn in the ER lumen via plasmodesmata, thereby promoting Mn movement toward vascular tissues in roots and subsequent long-distance transport to shoots.