Two Phloem Nitrate Transporters, NRT1.11 and NRT1.12, Are Important for Redistributing Xylem-Borne Nitrate to Enhance Plant Growth
Two Phloem Nitrate Transporters, NRT1.11 and NRT1.12, Are Important for Redistributing Xylem-Borne Nitrate to Enhance Plant Growth
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DOI：
10.1104/pp.113.226563
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发表时间：
2013-10-01
期刊：
影响因子：
7.4
通讯作者：
Tsay, Yi-Fang
中科院分区：
文献类型：
--
作者：
Hsu, Po-Kai;Tsay, Yi-Fang
这项对拟南芥硝酸盐转运蛋白NRT1.11和NRT1.12的研究揭示了木质部和韧皮部之间的相互作用如何确保硝酸盐在叶片中的最佳分布以促进植物生长。在非洲爪蟾卵母细胞中的功能分析表明，NRT1.11和NRT1.12都是低亲和力的硝酸盐转运蛋白。定量逆转录-聚合酶链反应和免疫印迹分析表明，这两个基因在较大的展开叶片中表达较高。绿色荧光蛋白和β-葡萄糖醛酸酶报告基因分析表明，NRT 1.11和NRT 1.12是质膜转运蛋白，在主静脉的伴细胞中表达。在nrt1.11和nrt1.12双突变体中，更多的根源（NO3-）-N-15被转运到成熟和较大的展开叶片中，但较少转运到最年轻的组织中，这表明NRT1.11和NRT1.12需要将根源的硝酸盐转移到成熟和较大展开叶片的主脉中的韧皮部中，再分配到最年轻的组织中。与野生型不同，nrt1.11和nrt1.12双突变体在高硝酸盐供应下没有表现出植物生长的增加。这些数据表明，NRT1.11和NRT1.12参与木质部到韧皮部的转移，将硝酸盐重新分配到发育中的叶片中，并且这样的硝酸盐重新分配是通过增加外部硝酸盐来增强植物最佳生长的关键步骤。
This study of the Arabidopsis (Arabidopsis thaliana) nitrate transporters NRT1.11 and NRT1.12 reveals how the interplay between xylem and phloem transport of nitrate ensures optimal nitrate distribution in leaves for plant growth. Functional analysis in Xenopus laevis oocytes showed that both NRT1.11 and NRT1.12 are low-affinity nitrate transporters. Quantitative reverse transcription-polymerase chain reaction and immunoblot analysis showed higher expression of these two genes in larger expanded leaves. Green fluorescent protein and beta-glucuronidase reporter analyses indicated that NRT1.11 and NRT1.12 are plasma membrane transporters expressed in the companion cells of the major vein. In nrt1.11 nrt1.12 double mutants, more root-fed (NO3-)-N-15 was translocated to mature and larger expanded leaves but less to the youngest tissues, suggesting that NRT1.11 and NRT1.12 are required for transferring root-derived nitrate into phloem in the major veins of mature and larger expanded leaves for redistributing to the youngest tissues. Distinct from the wild type, nrt1.11 nrt1.12 double mutants show no increase of plant growth at high nitrate supply. These data suggested that NRT1.11 and NRT1.12 are involved in xylem-to-phloem transfer for redistributing nitrate into developing leaves, and such nitrate redistribution is a critical step for optimal plant growth enhanced by increasing external nitrate.