Host plant genome overcomes the lack of a bacterial gene for symbiotic nitrogen fixation
Host plant genome overcomes the lack of a bacterial gene for symbiotic nitrogen fixation
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DOI：
10.1038/nature08594
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发表时间：
2009-11-26
期刊：
影响因子：
64.8
通讯作者：
Suganuma, Norio
中科院分区：
文献类型：
--
作者：
Hakoyama, Tsuneo;Niimi, Kaori;Suganuma, Norio
高柠檬酸盐是固氮酶中铁钼辅因子的一种成分，在固氮酶中发生固氮作用（1，2）。编码高柠檬酸合酶（HCS）（3）的NifV已从各种固氮生物中鉴定出来，但不存在于大多数根瘤菌物种中，所述根瘤菌物种仅在与豆类的共生关系中进行有效的固氮。在这里，我们表明，FEN 1基因的模式豆科植物，百脉根，克服了缺乏NifV的根瘤菌共生固氮。一种Fix（-）（非固定）植物突变体fen 1形成形态正常但无效的根瘤（4，5）。致病基因，FEN 1，被证明是编码HCS的能力，以补充一个HCS缺陷的酿酒酵母突变体。高柠檬酸是目前丰富的野生型结节，但无效fen 1结节缺席。接种携带FEN 1或棕色固氮菌NifV的百脉根中根瘤菌可修复FEN 1根瘤固氮活性的缺陷。外源高柠檬酸的供应也恢复固氮活性的fen 1根瘤通过从头固氮酶合成的根瘤菌类。这些结果表明，来源于宿主植物细胞的高柠檬酸盐对内共生体固氮酶系统的高效持续合成是必不可少的，从而为豆科植物与根瘤菌在共生固氮中的互补和不可或缺的伙伴关系提供了分子基础。
Homocitrate is a component of the iron-molybdenum cofactor in nitrogenase, where nitrogen fixation occurs(1,2). NifV, which encodes homocitrate synthase (HCS)(3), has been identified from various diazotrophs but is not present in most rhizobial species that perform efficient nitrogen fixation only in symbiotic association with legumes. Here we show that the FEN1 gene of a model legume, Lotus japonicus, overcomes the lack of NifV in rhizobia for symbiotic nitrogen fixation. A Fix(-) (non-fixing) plant mutant, fen1, forms morphologically normal but ineffective nodules(4,5). The causal gene, FEN1, was shown to encode HCS by its ability to complement a HCS-defective mutant of Saccharomyces cerevisiae. Homocitrate was present abundantly in wild-type nodules but was absent from ineffective fen1 nodules. Inoculation with Mesorhizobium loti carrying FEN1 or Azotobacter vinelandii NifV rescued the defect in nitrogen-fixing activity of the fen1 nodules. Exogenous supply of homocitrate also recovered the nitrogen-fixing activity of the fen1 nodules through de novo nitrogenase synthesis in the rhizobial bacteroids. These results indicate that homocitrate derived from the host plant cells is essential for the efficient and continuing synthesis of the nitrogenase system in endosymbionts, and thus provide a molecular basis for the complementary and indispensable partnership between legumes and rhizobia in symbiotic nitrogen fixation.