Zhao Xiyun, Song Yi, Wang Tianshu, Hua Chongchong, Hu Rui, Shang Yimin, Shi Haowen, Chen Sanfeng
Key Laboratory of Soil Microbiology of Agriculture Ministry and College of Biological Sciences, China Agricultural University , Beijing, China.
Appl Environ Microbiol. 2023 Sep 28;89(9):e0013923. doi: 10.1128/aem.00139-23. Epub 2023 Sep 5.
WLY78, a N-fixing bacterium, has great potential use as a biofertilizer in agriculture. Recently, we have revealed that GlnR positively and negatively regulates the transcription of the (trogen ixation) operon () in WLY78 by binding to two loci of the promoter according to nitrogen availability. However, the regulatory mechanisms of nitrogen metabolism mediated by GlnR in the genus remain unclear. In this study, we have revealed that glutamine synthetase (GS) and GlnR in WLY78 play a key role in the regulation of nitrogen metabolism. GS (encoded by within ) and GS1 (encoded by ) belong to distinct groups: GSI-α and GSI-β. Both GS and GS1 have the enzyme activity to convert NH and glutamate into glutamine, but only GS is involved in the repression by GlnR. GlnR represses transcription of under excess nitrogen, while it activates the expression of under nitrogen limitation. GlnR simultaneously activates and represses the expression of and in response to nitrogen availability. Also, GlnR regulates the expression of and . IMPORTANCE In this study, we have revealed that GlnR uses multiple mechanisms to regulate nitrogen metabolism. GlnR activates or represses or simultaneously activates and inhibits the transcription of nitrogen metabolism genes in response to nitrogen availability. The multiple regulation mechanisms employed by GlnR are very different from GlnR which represses nitrogen metabolism under excess nitrogen. Both GS encoded by within the operon and GS1 encoded by in WLY78 are involved in ammonium assimilation, but only GS is required for regulating GlnR activity. The work not only provides significant insight into understanding the interplay of GlnR and GS in nitrogen metabolism but also provides guidance for improving nitrogen fixation efficiency by modulating nitrogen metabolism.
WLY78是一种固氮细菌，在农业中作为生物肥料具有巨大的潜在用途。最近，我们发现GlnR根据氮的可利用性通过结合nif启动子的两个位点来正向和负向调节WLY78中nif（固氮）操纵子的转录。然而，GlnR介导的根瘤菌属氮代谢调控机制仍不清楚。在本研究中，我们发现WLY78中的谷氨酰胺合成酶（GS）和GlnR在氮代谢调控中起关键作用。GS（由nifA内的glnA编码）和GS1（由glnII编码）属于不同的组：GSI-α和GSI-β。GS和GS1都具有将NH₃和谷氨酸转化为谷氨酰胺的酶活性，但只有GS参与GlnR的抑制作用。在氮过量时，GlnR抑制nifA的转录，而在氮限制时它激活nifA的表达。GlnR根据氮的可利用性同时激活和抑制nifA和nifB的表达。此外，GlnR调节nifH和nifK的表达。重要性 在本研究中，我们发现GlnR利用多种机制调节氮代谢。GlnR根据氮的可利用性激活、抑制或同时激活和抑制氮代谢基因的转录。GlnR采用的多种调控机制与在氮过量时抑制氮代谢的其他GlnR非常不同。WLY78中nif操纵子内的glnA编码的GS和glnII编码的GS1都参与氨同化，但只有GS是调节GlnR活性所必需的。这项工作不仅为理解GlnR和GS在氮代谢中的相互作用提供了重要见解，也为通过调节氮代谢提高固氮效率提供了指导。
