Differential regulation of Rhizobium etli rpoN2 gene expression during symbiosis and free-living growth
Differential regulation of Rhizobium etli rpoN2 gene expression during symbiosis and free-living growth
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DOI：
10.1128/jb.180.14.3620-3628.1998
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发表时间：
1998-07-01
影响因子：
3.2
通讯作者：
Vanderleyden, J
中科院分区：
文献类型：
--
作者：
Michiels, J;Moris, M;Vanderleyden, J
最近表征了编码替代性σ因子σ（54）（RpoN）的Rizobium etli rpoN 1基因，并显示其在自由生活的有氧生长期间参与几种氮和碳源的同化（J. Mesels，T.货车索姆岛D'hooghe，B，Dombrecht，T，Benhassine，P，de Wilde，and J，Vanderleyden，J，Bacteriol. 180：1729-1740，1998），我们在R. etli，rpoN 2，编码54.0kDa的蛋白质，与R. etli RpoN 1蛋白。rpoN 2基因与一个短的开放阅读框orf 180共转录，orf 180编码一个大小为20.1 kDa的蛋白，该蛋白与几种大小相似的原核和真核蛋白同源。与R. etli rpoN 1突变株中，rpoN 2基因的失活在自由生长期间不产生任何表型缺陷。然而，共生固氮减少了约90%的rpoN 2突变体，而野生型固氮水平观察到的rpoN 1突变株，固氮完全废除rpoN 1 rpoN 2双突变体。rpoN 1的表达在有氧生长过程中是负自调节的，在微好氧和共生过程中减少。与此相反，rpoN 2-gusA和orf 180-gusA融合不需氧表达，但强烈诱导低氧张力或类杆菌。rpoN 2和orf 180的表达在R.在所有测试条件下etli rpoN 1 rpoN 2和nifA突变体。在自由生活的微需氧条件下，rpoN 2和orf 180的转录需要RpoN 1蛋白。在共生中，rpoN 2和orf 180的表达独立于rpoN 1基因发生，表明存在另一种共生特异性转录激活机制。
The Rizobium etli rpoN1 gene, encoding the alternative sigma factor sigma(54) (RpoN), was recently characterized and shown to be involved in the assimilation of several nitrogen and carbon sources during free-living aerobic growth (J. Michiels, T. Van Soom, I. D'hooghe, B, Dombrecht, T, Benhassine, P, de Wilde, and J, Vanderleyden, J, Bacteriol. 180:1729-1740, 1998), We identified a second rpoN gene copy in R. etli, rpoN2, encoding a 54.0 kDa protein which displays 59% amino acid identity with the R. etli RpoN1 protein. The rpoN2 gene is cotranscribed with a short open reading frame, orf180, which codes for a protein with a size of 20.1 kDa that is homologous to several prokaryotic and eukaryotic proteins of similar size. In contrast to the R. etli rpoN1 mutant strain, inactivation of the rpoN2 gene did not produce any phenotypic defects during free-living growth. However, symbiotic nitrogen fixation was reduced by approximately 90% in the rpoN2 mutant, whereas wild-type levels of nitrogen fixation were observed in the rpoN1 mutant strain, Nitrogen fi ration was completely abolished in the rpoN1 rpoN2 double mutant. Expression of rpoN1 was negatively autoregulated during aerobic growth and was reduced during microaerobiosis and symbiosis. In contrast, rpoN2-gusA and orf180-gusA fusions were not expressed aerobically but were strongly induced at low oxygen tensions or in bacteroids. Expression of rpoN2 and orf180 was abolished in R. etli rpoN1 rpoN2 and nifA mutants under all conditions tested. Under free-living microaerobic conditions, transcription of rpoN2 and orf180 required the RpoN1 protein. In symbiosis, expression of rpoN2 and orf180 occurred independently of the rpoN1 gene, suggesting the existence of an alternative symbiosis-specific mechanism of transcription activation.