A Rice Phenolic Efflux Transporter Is Essential for Solubilizing Precipitated Apoplasmic Iron in the Plant Stele
A Rice Phenolic Efflux Transporter Is Essential for Solubilizing Precipitated Apoplasmic Iron in the Plant Stele
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DOI：
10.1074/jbc.m111.221168
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发表时间：
2011-07-15
影响因子：
4.8
通讯作者：
Nishizawa, Naoko K.
中科院分区：
文献类型：
--
作者：
Ishimaru, Yasuhiro;Kakei, Yusuke;Nishizawa, Naoko K.
缺铁是主要的农业问题之一，因为世界上30%的可耕地碱性太强，无法实现最佳作物生产，导致植物缺乏可用的铁，尽管铁丰富。植物分泌酚类物质，如原儿茶酸（PCA）和咖啡酸，以吸收外质沉淀铁。铁摄取策略的分子途径和基因已经被明确，而酚类物质的合成和分泌的分子机制尚未明确，植物中还没有发现酚类物质的外排转运体。本文描述了水稻中酚类物质外排转运体的鉴定。我们发现了一个富集镉的水稻突变体，其木质部汁液中PCA和咖啡酸的含量显著降低，因此将其命名为酚类外流零1 （phenolics efflux zero 1, pez1）。PEZ1在非洲爪蟾卵母细胞中表达时定位于质膜并转运PCA。PEZ1主要定位于根柱。在pez1的根部，沉淀的外质铁增加。PEZ1过表达系的生长受到严重限制，这些系积累了更多的铁，这是由于沉淀的铁在石碑中高度溶解的结果。我们发现，PEZ1是木质部汁液中PCA浓度增加的原因，并且对柱体中外质沉淀铁的利用至关重要。
Iron deficiency is one of the major agricultural problems, as 30% of the arable land of the world is too alkaline for optimal crop production, rendering plants short of available iron despite its abundance. To take up apoplasmic precipitated iron, plants secrete phenolics such as protocatechuic acid (PCA) and caffeic acid. The molecular pathways and genes of iron uptake strategies are already characterized, whereas the molecular mechanisms of phenolics synthesis and secretion have not been clarified, and no phenolics efflux transporters have been identified in plants yet.Here we describe the identification of a phenolics efflux transporter in rice. We identified a cadmium-accumulating rice mutant in which the amount of PCA and caffeic acid in the xylem sap was dramatically reduced and hence named it phenolics efflux zero 1 (pez1). PEZ1 localized to the plasma membrane and transported PCA when expressed in Xenopus laevis oocytes. PEZ1 localized mainly in the stele of roots. In the roots of pez1, precipitated apoplasmic iron increased. The growth of PEZ1 overexpression lines was severely restricted, and these lines accumulated more iron as a result of the high solubilization of precipitated apoplasmic iron in the stele. We show that PEZ1 is responsible for an increase of PCA concentration in the xylem sap and is essential for the utilization of apoplasmic precipitated iron in the stele.