College of Life Science, Hunan Normal University, Changsha 410081, China.
J Integr Plant Biol. 2008 Dec;50(12):1530-8. doi: 10.1111/j.1744-7909.2008.00770.x.
Magnesium (Mg(2+)) is one of the essential cations in all cells. Although the Mg(2+) transport mechanism has been well-documented in bacteria, less is known about Mg(2+) transporters in eukaryotes. The AtMGT gene family encoding putative magnesium transport proteins had been described previously. We report here that one of the Arabidopsis MGT family members, the AtMGT7 gene, encodes two mRNAs that have resulted from alternative splicing variants, designated AtMGT7a and AtMGT7b. Interestingly, the two mRNA variants were expressed with different patterns with AtMGT7a expressing in all organs, but AtMGT7b appearing only in root and flowers. The AtMGT7a variant functionally complemented a bacterial mutant lacking Mg(2+) transport capacity, whereas AtMGT7b did not. The (63)Ni(2+) tracer uptake analysis in the bacterial model showed that AtMGT7a mediated low-affinity transport of Mg(2+). Consistent with the complementation assay result, (63)Ni(2+) tracer uptake analysis revealed that AtMGT7b did not transport Mg(2+). This study therefore has identified from a higher plant the first low-affinity Mg(2+) transporter encoded by a gene with alternatively spliced transcripts that produce proteins with distinct functions.
镁（Mg(2+)）是所有细胞中必需的阳离子之一。尽管细菌中的 Mg(2+)转运机制已经得到很好的描述，但对于真核生物中的 Mg(2+)转运蛋白知之甚少。先前已经描述了编码假定镁转运蛋白的 AtMGT 基因家族。我们在这里报告，拟南芥 MGT 家族的一个成员，AtMGT7 基因，编码两个由选择性剪接变体产生的 mRNA，分别命名为 AtMGT7a 和 AtMGT7b。有趣的是，这两个 mRNA 变体的表达模式不同，AtMGT7a 在所有器官中表达，但 AtMGT7b 仅在根和花中表达。AtMGT7a 变体可有效补充缺乏 Mg(2+)转运能力的细菌突变体，而 AtMGT7b 则不能。在细菌模型中的 (63)Ni(2+)示踪剂摄取分析表明，AtMGT7a 介导 Mg(2+)的低亲和力转运。与互补测定结果一致，(63)Ni(2+)示踪剂摄取分析表明 AtMGT7b 不转运 Mg(2+)。因此，本研究从高等植物中鉴定出第一个具有不同功能的蛋白的低亲和力 Mg(2+)转运蛋白，该蛋白由具有选择性剪接转录本的基因编码。
