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Gene Structure and Expression of the High-affinity Nitrate Transport System in Rice Roots

Authors

  • Chao Cai,

    1. State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
    2. Research Center for Eco-environmental Sciences, the Chinese Academy of Sciences, Beijing 100085, China
    3. Graduated University, the Chinese Academy of Sciences, Beijing 100049, China
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  • Jun-Yi Wang,

    1. State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
    2. Graduated University, the Chinese Academy of Sciences, Beijing 100049, China
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  • Yong-Guan Zhu,

    1. Research Center for Eco-environmental Sciences, the Chinese Academy of Sciences, Beijing 100085, China
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  • Qi-Rong Shen,

    1. College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing 210095, China)
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  • Bin Li,

    1. State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
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  • Yi-Ping Tong,

    Corresponding author
    1. State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
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  • Zhen-Sheng Li

    Corresponding author
    1. State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences, Beijing 100101, China
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  • Supported by the National Natural Science Foundation of China (30390080 and 30521001) and the Ministry of Science and Technology of China (2005CB120900 and 2004CB117200).

*Authors for correspondence.
Tel(Fax): +86 (0)10 6488 9381;
E-mail: <yptong@genetics.ac.cn> and <zsli@genetics.ac.cn>.

Abstract

Rice has a preference for uptake of ammonium over nitrate and can use ammonium-N efficiently. Consequently, transporters mediating ammonium uptake have been extensively studied, but nitrate transporters have been largely ignored. Recently, some reports have shown that rice also has high capacity to acquire nitrate from growth medium, so understanding the nitrate transport system in rice roots is very important for improving N use efficiency in rice. The present study identified four putative NRT2 and two putative NAR2 genes that encode components of the high-affinity nitrate transport system (HATS) in the rice (Oryza sativa L. subsp. japonica cv. Nipponbare) genome. OsNRT2.1 and OsNRT2.2 share an identical coding region sequence, and their deduced proteins are closely related to those from mono-cotyledonous plants. The two NAR2 proteins are closely related to those from mono-cotyledonous plants as well. However, OsNRT2.3 and OsNRT2.4 are more closely related to Arabidopsis NRT2 proteins. Relative quantitative reverse transcription-polymerase chain reaction analysis showed that all of the six genes were rapidly upregulated and then downregulated in the roots of N-starved rice plants after they were re-supplied with 0.2 mM nitrate, but the response to nitrate differed among gene members. The results from phylogenetic tree, gene structure and expression analysis implied the divergent roles for the individual members of the rice NRT2 and NAR2 families. High-affinity nitrate influx rates associated with nitrate induction in rice roots were investigated and were found to be regulated by external pH. Compared with the nitrate influx rates at pH 6.5, alkaline pH (pH 8.0) inhibited nitrate influx, and acidic pH (pH 5.0) enhanced the nitrate influx in 1 h nitrate induced roots, but did not significantly affect that in 4 to 8 h nitrate induced roots.

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