The NifA-RpoN regulon of Mesorhizobium loti strain R7A and its symbiotic activation by a novel LacI/GalR-family regulator.
The NifA-RpoN regulon of Mesorhizobium loti strain R7A and its symbiotic activation by a novel LacI/GalR-family regulator.
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DOI：
10.1371/journal.pone.0053762
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发表时间：
2013
期刊：
影响因子：
3.7
通讯作者：
Ronson CW
中科院分区：
文献类型：
--
作者：
Sullivan JT;Brown SD;Ronson CW
loti中根瘤菌是包括模式豆科植物L. japonicus在内的莲花种的微共生体。与其他根瘤菌不同的是，它含有两个关键的固氮调控基因nifA， nifA1和nifA2，这两个基因都位于共生岛ICEMlSymR7A上。M. loti R7A也含有两个rpona基因，rpoN1位于ICEMlSymR7A外的染色体上，rpoN2位于ICEMlSymR7A上。当前工作的目的是确定nifA表达如何在M. loti中被激活，并表征nifA - rpon调控子。nifA2和rpoN2基因对固氮至关重要，而nifA1和rpoN1基因则是可有可无的。nifA2的表达可能是由位于nifA2上游的fixV基因编码的LacI/GalR家族的一个新的调节因子激活的，这可能是对肌醇衍生物的反应。除了特征明确的nif/fix基因外，大多数nifa2调节基因虽然在根瘤中强烈表达，但不是固氮所必需的。nifa调控的nifZ和fixU基因，以及不受nifa调控的nifQ基因，在M. loti中是完全有效的共生所必需的，尽管它们不存在于其他一些根瘤菌中。nifa调控的编码孔蛋白的基因msi158也是完全有效的共生所必需的。一些缺乏nifa2调控启动子的代谢基因在结节中以依赖nifa2的方式强烈表达，但突变体没有明显的共生表型。综上所述，ICEMlSymR7A上编码的许多基因在根瘤中强烈表达，但在自由生活的根瘤菌中不表达，但对共生固氮不是必需的。似乎这些基因中的一些在基因组的其他地方有功能同源物，并且类细菌代谢可能具有足够的可塑性，以适应某些酶功能的丧失。
Mesorhizobium loti is the microsymbiont of Lotus species, including the model legume L. japonicus. M. loti differs from other rhizobia in that it contains two copies of the key nitrogen fixation regulatory gene nifA, nifA1 and nifA2, both of which are located on the symbiosis island ICEMlSymR7A. M. loti R7A also contains two rpoN genes, rpoN1 located on the chromosome outside of ICEMlSymR7A and rpoN2 that is located on ICEMlSymR7A. The aims of the current work were to establish how nifA expression was activated in M. loti and to characterise the NifA-RpoN regulon. The nifA2 and rpoN2 genes were essential for nitrogen fixation whereas nifA1 and rpoN1 were dispensable. Expression of nifA2 was activated, possibly in response to an inositol derivative, by a novel regulator of the LacI/GalR family encoded by the fixV gene located upstream of nifA2. Other than the well-characterized nif/fix genes, most NifA2-regulated genes were not required for nitrogen fixation although they were strongly expressed in nodules. The NifA-regulated nifZ and fixU genes, along with nifQ which was not NifA-regulated, were required in M. loti for a fully effective symbiosis although they are not present in some other rhizobia. The NifA-regulated gene msi158 that encodes a porin was also required for a fully effective symbiosis. Several metabolic genes that lacked NifA-regulated promoters were strongly expressed in nodules in a NifA2-dependent manner but again mutants did not have an overt symbiotic phenotype. In summary, many genes encoded on ICEMlSymR7A were strongly expressed in nodules but not free-living rhizobia, but were not essential for symbiotic nitrogen fixation. It seems likely that some of these genes have functional homologues elsewhere in the genome and that bacteroid metabolism may be sufficiently plastic to adapt to loss of certain enzymatic functions.
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影响因子：
3.5
作者：
Dombrecht, B;Vanderleyden, J;Michiels, J
通讯作者：
Michiels, J
影响因子：
3.5
作者：
FELLAY, R;KRISCH, HM;FREY, J
通讯作者：
FREY, J
影响因子：
10.7
作者：
Fukami-Kobayashi, K;Tateno, Y;Nishikawa, K
通讯作者：
Nishikawa, K
影响因子：
3.5
作者：
Baumberger, IC;Fraefel, N;Hennecke, H
通讯作者：
Hennecke, H
DOI：
10.1016/j.bbapap.2009.01.002
发表时间：
2009-04
期刊：
Biochimica et biophysica acta
影响因子：
--
作者：
Buchko GW;Robinson H;Addlagatta A
通讯作者：
Addlagatta A