FixJ:: a major regulator of the oxygen limitation response and late symbiotic functions of Sinorhizobium meliloti
FixJ:: a major regulator of the oxygen limitation response and late symbiotic functions of Sinorhizobium meliloti
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DOI：
10.1128/jb.00251-06
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发表时间：
2006-07-01
影响因子：
3.2
通讯作者：
Batut, Jacques
中科院分区：
文献类型：
--
作者：
Bobik, Christine;Meilhoc, Eliane;Batut, Jacques
苜蓿中华根瘤菌既可以在土壤中自由生活，也可以在豆科植物根瘤中共生，在根瘤中细菌分化为固氮类杆菌。参与固氮和相关呼吸作用的基因的表达分别由两个中间调节因子NifA和FixK控制，这两个中间调节因子分别由响应于低氧条件的双组分调节系统FixLJ控制。为了鉴定FixLJ调节子，在微需氧自由活细胞中以及在野生型和fixJ无效突变菌株的细菌的共生生命期间测定基因表达谱。我们确定了FixJ在两种状态下激活的122个基因，包括87个新靶点。FixJ控制74%的在微需氧（2%氧）中诱导的基因和在成熟类菌体中表达的大多数基因。97%的FixJ激活基因位于共生质粒pSymA上。nifA和fixK突变体的转录组图谱显示，NifA激活有限数量的基因，所有特定的共生状态，而FixK控制超过90个基因，参与自由生活和/或共生生活。这项研究还表明，FixJ除了已知的靶点外，没有其他直接靶点。FixJ参与诸如脱氮或氨基酸/多胺代谢和运输的功能的调节。在选定的新的FixJ目标的突变并没有影响细菌的能力，形成紫花苜蓿根固氮根瘤。根据这些结果，我们提出了一个更新的模型的FixJ调节子。
Sinorhizobium meliloti exists either in a free-living state in the soil or in symbiosis within legume nodules, where the bacteria differentiate into nitrogen-fixing bacteroids. Expression of genes involved in nitrogen fixation and associated respiration is governed by two intermediate regulators, NifA and FixK, respectively, which are controlled by a two-component regulatory system FixLJ in response to low-oxygen conditions. In order to identify the FixLJ regulon, gene expression profiles were determined in microaerobic free-living cells as well as during the symbiotic life of the bacterium for the wild type and a fixJ null-mutant strain. We identified 122 genes activated by FixJ in either state, including 87 novel targets. FixJ controls 74% of the genes induced in microaerobiosis (2% oxygen) and the majority of genes expressed in mature bacteroids. Ninety-seven percent of FixJ-activated genes are located on the symbiotic plasmid pSymA. Transcriptome profiles of a nifA and a fixK mutant showed that NifA activates a limited number of genes, all specific to the symbiotic state, whereas FixK controls more than 90 genes, involved in free-living and/or symbiotic life. This study also revealed that FixJ has no other direct targets besides those already known. FixJ is involved in the regulation of functions such as denitrification or amino acid/polyamine metabolism and transport. Mutations in selected novel FixJ targets did not affect the ability of the bacteria to form nitrogen-fixing nodules on Medicago sativa roots. From these results, we propose an updated model of the FixJ regulon.