2 C4-DICARBOXYLATE TRANSPORT-SYSTEMS IN RHIZOBIUM SP NGR234 - RHIZOBIAL DICARBOXYLATE TRANSPORT IS ESSENTIAL FOR NITROGEN-FIXATION IN TROPICAL LEGUME SYMBIOSES
2 C4-DICARBOXYLATE TRANSPORT-SYSTEMS IN RHIZOBIUM SP NGR234 - RHIZOBIAL DICARBOXYLATE TRANSPORT IS ESSENTIAL FOR NITROGEN-FIXATION IN TROPICAL LEGUME SYMBIOSES
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DOI：
10.1094/mpmi-5-179
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发表时间：
1992-03-01
影响因子：
3.5
通讯作者：
STANLEY, J
中科院分区：
文献类型：
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作者：
VANSLOOTEN, JC;BHUVANASVARI, TV;STANLEY, J
为了研究二羧酸转运在根瘤菌和热带豆科植物之间固氮共生中的作用，我们对根瘤菌的细菌转运系统进行了分子遗传学分析。 NGR234。这种广泛的宿主范围菌株固定氮与进化上不同的豆科植物有关。从根瘤菌 NGR234 中克隆了两个二羧酸转运系统。其中一个位点位于染色体上，而另一个位点则携带在共生质粒（pSym）上，并含有 dctA 载体蛋白基因，对此进行了详细分析。尽管该结构基因的DNA和衍生氨基酸序列与苜蓿根瘤菌的DNA和衍生氨基酸序列基本同源，但其启动子序列却截然不同，并且上游序列也与苜蓿根瘤菌中该位置发现的dctB没有同源性。 NGR234 dctA 中的定点内部缺失突变体表现出（独特的）完全共生表型，可以在植物外的二羧酸盐上生长，但不能在植物中固氮。在具有确定型或不确定型根瘤的 NGR234 测试宿主植物中发现了这种表型，首次证实了共生体特异性吸收二羧酸盐是热带豆科植物共生体中固氮的先决条件。
To investigate the role of dicarboxylate transport in nitrogen-fixing symbioses between Rhizobium and tropical legumes, we made a molecular genetic analysis of the bacterial transport system in Rhizobium sp. NGR234. This broad host range strain fixes nitrogen in association with evolutionarily divergent legumes. Two dicarboxylate transport systems were cloned from Rhizobium NGR234. One locus was chromosomally located, whereas the other was carried on the symbiotic plasmid (pSym) and contained a dctA carrier protein gene, which was analyzed in detail. Although the DNA and derived amino acid sequences of the structural gene were substantially homologous to that of R. meliloti, its promoter sequence was quite distinct, and the upstream sequence also exhibited no homology to dctB, which is found at this position in R. meliloti. A site-directed internal deletion mutant in dctA of NGR234 exhibited a (unique) exclusively symbiotic phenotype that could grow on dicarboxylates ex planta, but could not fix nitrogen in planta. This phenotype was found for tested host plants of NGR234 with either determinate- or indeterminate-type nodules, confirming for the first time that symbiosis-specific uptake of dicarboxylates is a prerequisite for nitrogen fixation in tropical legume symbioses.