Metal Tolerance Protein 8 Mediates Manganese Homeostasis and Iron Reallocation during Seed Development and Germination
Metal Tolerance Protein 8 Mediates Manganese Homeostasis and Iron Reallocation during Seed Development and Germination
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DOI：
10.1104/pp.16.01646
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发表时间：
2017-07-01
期刊：
影响因子：
7.4
通讯作者：
von Wiren, Nicolaus
中科院分区：
文献类型：
--
作者：
Eroglu, Seckin;Giehl, Ricardo F. H.;von Wiren, Nicolaus
种子中的金属积累是植物萌发和生长的先决条件，也是向人类提供微量营养素的必要条件。为了研究种子中金属运输过程及其相互作用，我们聚焦于金属耐受蛋白8（MTP8），它是阳离子扩散促进剂锰（Mn）亚家族的液泡膜转运蛋白，在拟南芥（Arabidopsis thaliana）中在种子的胚中表达。X射线荧光成像显示，MTP8的表达导致锰在子叶远轴侧的表皮下细胞以及下胚轴的皮层细胞中定位。因此，在锰可利用性较低的情况下，MTP8增加了种子中锰的储存量，这是种子有效萌发所必需的。在缺乏液泡铁转运蛋白1（VIT1）表达的突变体胚中，MTP8在表达MTP8的细胞类型中形成铁（Fe）热点，这表明MTP8除了运输锰之外还运输铁。在mtp8 vit1双突变体种子中，锰和铁分布在胚的所有细胞类型中。MTP8的铁运输功能通过其能够弥补液泡铁运输缺陷型酵母突变体的铁超敏感性得以证实。在有锰存在的情况下浸泡mtp8 - 1突变体种子或使种子经历干湿循环表明，MTP8赋予了对锰的耐受性。在萌发过程中，MTP8促进了铁从维管束的重新分配。这些结果表明，种子中锰和铁在细胞类型特异性的积累依赖于MTP8，并且这种转运蛋白在种子金属储存的产生以及在具有挑战性的环境条件下的金属稳态和萌发效率方面发挥着重要作用。
Metal accumulation in seeds is a prerequisite for germination and establishment of plants but also for micronutrient delivery to humans. To investigate metal transport processes and their interactions in seeds, we focused on METAL TOLERANCE PROTEIN8 (MTP8), a tonoplast transporter of the manganese (Mn) subclade of cation diffusion facilitators, which in Arabidopsis (Arabidopsis thaliana) is expressed in embryos of seeds. The x-ray fluorescence imaging showed that expression of MTP8 was responsible for Mn localization in subepidermal cells on the abaxial side of the cotyledons and in cortical cells of the hypocotyl. Accordingly, under low Mn availability, MTP8 increased seed stores of Mn, required for efficient seed germination. In mutant embryos lacking expression of VACUOLAR IRON TRANSPORTER1 (VIT1), MTP8 built up iron (Fe) hotspots in MTP8-expressing cells types, suggesting that MTP8 transports Fe in addition to Mn. In mtp8 vit1 double mutant seeds, Mn and Fe were distributed in all cell types of the embryo. An Fe transport function of MTP8 was confirmed by its ability to complement Fe hypersensitivity of a yeast mutant defective in vacuolar Fe transport. Imbibing mtp8-1 mutant seeds in the presence of Mn or subjecting seeds to wet-dry cycles showed that MTP8 conferred Mn tolerance. During germination, MTP8 promoted reallocation of Fe from the vasculature. These results indicate that cell type-specific accumulation of Mn and Fe in seeds depends on MTP8 and that this transporter plays an important role in the generation of seed metal stores as well as for metal homeostasis and germination efficiency under challenging environmental conditions.