Functional characterization and expression analysis of a gene, OsENT2, encoding an equilibrative nucleoside transporter in rice suggest a function in cytokinin transport
Functional characterization and expression analysis of a gene, OsENT2, encoding an equilibrative nucleoside transporter in rice suggest a function in cytokinin transport
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DOI：
10.1104/pp.105.060137
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发表时间：
2005-05-01
期刊：
影响因子：
7.4
通讯作者：
Sakakibara, H
中科院分区：
文献类型：
--
作者：
Hirose, N;Makita, N;Sakakibara, H
我们确定了四个基因的潜在平衡核苷转运蛋白（ENTs）从水稻（水稻;指定OsENT 1到OsENT 4）。对表达OsENTs的芽殖酵母（Saccharomyces cerevisiae）细胞的生长分析表明，OsENT 2以高亲和力转运腺苷和尿苷（腺苷，K-m = 3.0 μ M;尿苷，K-m = 0.7 μ M）。嘌呤或嘧啶核苷和2' -脱氧核苷强烈抑制OsENT 2的腺苷转运，表明OsENT 2具有广泛的底物特异性。OsENT 2介导的腺苷转运对哺乳动物ENTs的典型抑制剂硝基苄基巯基嘌呤核糖核苷、地拉卓和双嘧达莫具有抗性。运输活性在pH 5.0时最大，在较低和较高pH时略有下降。在与各种细胞分裂素的竞争实验中，OsENT 2的腺苷运输被异戊烯基腺嘌呤核苷（iPR）抑制。用放射性标记的细胞分裂素的直接测量表明，OsENT 2介导的iPR（Km = 32 μ M）和反式玉米素核苷（Km = 660 μ M）的摄取，表明OsENT 2参与植物中的iPR运输。在成熟植株中，OsENT 2主要在根中表达。OsENT 2启动子驱动β-葡萄糖醛酸酶报告基因在萌发期间的盾片中和萌发植物的维管组织中表达，表明OsENT 2分别参与萌发胚对胚乳来源的核苷的回收和生长植物中核苷的长距离运输.
We identified four genes for potential equilibrative nucleoside transporters ( ENTs) from rice ( Oryza sativa; designated OsENT1 through OsENT4). Growth analysis of budding yeast ( Saccharomyces cerevisiae) cells expressing OsENTs showed that OsENT2 transported adenosine and uridine with high affinity ( adenosine, K-m = 3.0 mu M; uridine, K-m = 0.7 mu M). Purine or pyrimidine nucleosides and 2' -deoxynucleosides strongly inhibited adenosine transport via OsENT2, suggesting that OsENT2 possesses broad substrate specificity. OsENT2- mediated adenosine transport was resistant to the typical inhibitors of mammalian ENTs, nitrobenzylmercaptopurine ribonucleoside, dilazep, and dipyridamole. The transport activity was maximal at pH 5.0 and decreased slightly at lower as well as higher pH. In competition experiments with various cytokinins, adenosine transport by OsENT2 was inhibited by isopentenyladenine riboside ( iPR). Direct measurements with radiolabeled cytokinins demonstrated that OsENT2 mediated uptake of iPR ( K-m = 32 mu M) and trans- zeatin riboside ( Km = 660 mu M), suggesting that OsENT2 participates in iPR transport in planta. In mature plants, OsENT2 was predominantly expressed in roots. The OsENT2 promoter drove the expression of the beta- glucuronidase reporter gene in the scutellum during germination and in vascular tissues in germinated plants, suggesting a participation of OsENT2 in the retrieval of endosperm- derived nucleosides by the germinating embryo and in the long- distance transport of nucleosides in growing plants, respectively.