Transcription Regulation of Cell Cycle Regulatory Genes Mediated by NtrX to Affect Sinorhizobium meliloti Cell Division

Abstract

The cell division of the alfalfa symbiont, Sinorhizobium meliloti, is dictated by a cell cycle regulatory pathway containing the key transcription factors CtrA, GcrA, and DnaA. In this study, we found that NtrX, one of the regulators of nitrogen metabolism, can directly regulate the expression of ctrA, gcrA, and dnaA from the cell cycle pathway. Three sets of S. meliloti ntrX mutants showed similar cell division defects, such as slow growth, abnormal morphology of some cells, and delayed DNA synthesis. Transcription of ctrA and gcrA was upregulated, whereas the transcription of dnaA and ftsZ1 was downregulated in the insertion mutant and the strain of Sm1021 expressing ntrXD53E. Correspondingly, the inducible transcription of ntrX activates the expression of dnaA and ftsZ1, but represses ctrA and gcrA in the depletion strain. The expression levels of CtrA and GcrA were confirmed by Western blotting. The transcription regulation of these genes requires phosphorylation of the conserved 53rd aspartate in the NtrX protein that binds directly to the promoter regions of ctrA, gcrA, dnaA, and ftsZ1 by recognizing the characteristic sequence CAAN2-5TTG. Our findings suggest that NtrX affects S. meliloti cell division by regulating the transcription of the key cell cycle regulatory genes.

Proteomic survey of the DNA damage response inCaulobacter crescentus

“…Our Tn-seq results identified six of these genes as more likely to contain transposon insertions upon MMC damage: CCNA_03681: ABC transporter ATP-binding protein, CCNA_00299: PurD, CCNA_00099: FzlC, CCNA_01034: TonB-dependent outer membrane receptor, and CCNA_01817: NtrX. We decided to focus on PurD and FzlC for further characterization as membrane proteins may alter MMC import and NtrX might have confounding effects because of its role in cell cycle regulation (21, 22).…”

A protease and a lipoprotein jointly modulate the conserved ExoR-ExoS-ChvI signaling pathway critical inSinorhizobium melilotifor symbiosis with legume hosts

“…Nevertheless, other possible explanations, not mutually exclusive, can also account for JspA's involvement in resistance against cell envelope assaults: for example, JspA may degrade other substrates or signaling pathways under specific conditions, or JspA and LppA may assist in the proper construction of the cell envelope by ensuring proper maturation of other lipoproteins. Furthermore, a number of other signaling systems, such as ActK-ActJ, CenK-CenR, CpxA-CpxR, EmmB-EmmC, FeuQ-FeuP, and NtrX-NtrY, contribute to the maintenance of cell envelope integrity in rhizobia (Albicoro et al, 2021;Albicoro et al, 2023;Bensig et al, 2022;Calatrava-Morales et al, 2017;Lakey et al, 2022;Morris & Gonzalez, 2009;Santos et al, 2010;VanYperen et al, 2015;Wang et al, 2013;Xing et al, 2022), and how these different systems cooperate with ExoS-ChvI to ensure successful symbiosis remains ripe for further investigation.…”

A protease and a lipoprotein jointly modulate the conserved ExoR-ExoS-ChvI signaling pathway critical in Sinorhizobium meliloti for symbiosis with legume hosts

“…Nevertheless, other possible explanations, not mutually exclusive, can also account for JspA's involvement in resistance against cell envelope assaults: for example, JspA may degrade other substrates or signaling pathways under specific conditions, or JspA and LppA may assist in the proper construction of the cell envelope by ensuring proper maturation of other lipoproteins. Furthermore, a number of other signaling systems, such as ActK-ActJ, CenK-CenR, CpxA-CpxR, EmmB-EmmC, FeuQ-FeuP, and NtrX-NtrY, contribute to the maintenance of cell envelope integrity in S. meliloti [46,55,[134][135][136][137][138][139][140][141][142][143], and how these different systems cooperate with ExoS-ChvI to ensure successful symbiosis remains ripe for further investigation.…”