Tianshu Wang, Xiyun Zhao, Haowen Shi, Li Sun, Yongbin Li, Qin Li, Jilun Li. Positive and negative regulation of transferred nif genes mediated by indigenous GlnR in Gram-positive Paenibacillus polymyxa. PLOS Genetics. DOI: org/10.1371/journal.pgen.1007629
发布日期:2019-11-11 浏览次数:  信息来源:生物学院

Positive and negative regulation of transferred nif genes mediated by indigenous GlnR in Gram-positive Paenibacillus polymyxa

Tianshu Wang, Xiyun Zhao, Haowen Shi, Li Sun, Yongbin Li, Qin Li, Haowei Zhang, Sanfeng Chen, Jilun Li

 

PLOS Genetics

DOI: org/10.1371/journal.pgen.1007629

 

Abstract

Ammonia is a major signal that regulates nitrogen fixation in most diazotrophs. Regulation of nitrogen fixation by ammonia in the Gram-negative diazotrophs is well-characterized. In these bacteria, this regulation occurs mainly at the level of nif (nitrogen fixation) gene transcription, which requires a nif-specific activator, NifA. Although Gram-positive and diazotrophic Paenibacilli have been extensively used as a bacterial fertilizer in agriculture, how nitrogen fixation is regulated in response to nitrogen availability in these bacteria remains unclear. An indigenous GlnR and GlnR/TnrA-binding sites in the promoter region of the nif cluster are conserved in these strains, indicating the role of GlnR as a regulator of nitrogen fixation. In this study, we for the first time reveal that GlnR of Paenibacillus polymyxa WLY78 is essentially required for nif gene transcription under nitrogen limitation, whereas both GlnR and glutamine synthetase (GS) encoded by glnA within glnRA operon are required for repressing nif expression under excess nitrogen. Dimerization of GlnR is necessary for binding of GlnR to DNA. GlnR in P. polymyxa WLY78 exists in a mixture of dimers and monomers. The C-terminal region of GlnR monomer is an autoinhibitory domain that prevents GlnR from binding DNA. Two GlnR-biding sites flank the -35/-10 regions of the nif promoter of the nif operon (nifBHDKENXhesAnifV). The GlnR-binding site(located upstream of -35/-10 regions of the nif promoter) is specially required for activating nif transcription, while GlnR-binding site(located downstream of -35/-10 regions of the nif promoter) is for repressing nif expression. Under nitrogen limitation, GlnR dimer binds to GlnRbinding sitein a weak and transient association way and then activates nif transcription. During excess nitrogen, glutamine binds to and feedback inhibits GS by forming the complex FBI-GS. The FBI-GS interacts with the C-terminal domain of GlnR and stabilizes the binding affinity of GlnR to GlnR-binding siteand thus represses nif transcription.


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