The General Stress Response in Alpha‐Rhizobia

Sauviac, Laurent; Bastiat, Bénédicte; Bruand, Claude

doi:10.1002/9781119053095.ch40

Cited by 2 publications

(4 citation statements)

References 70 publications

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“…The GSR in alphaproteobacteria is mediated by some but not all group ECF15 σs ( 20 , 40 , 41 ). RpoE2 is the GSR σ factor in S. meliloti ( 21 , 42 ).…”

Section: Resultsmentioning

confidence: 99%

“…Activity of alphaproteobacterial GSR σs is regulated via a partner-switching mechanism: a cytoplasmic anti-σ (RsiA1/RsiA2 in S. meliloti ) sequesters σ from interacting with RNAP, until an anti-anti-σ (RsiB1/RsiB2) is activated by phosphorylation of its receiver domain ( 42 , 47 ). Such phosphorylation allows anti-anti-σ to bind the anti-σ, releasing σ for interaction with RNAP ( 20 , 47 ).…”

Section: Resultsmentioning

confidence: 99%

“…GSR σs are not required for normal symbiosis in S. meliloti , R. etli , and Rhizobium leguminosarum bv. viciae , perhaps due to redundant regulatory systems ( 20 ). In contrast, B. diazoefficiens ecfG mutants show severe nodulation defects because a functional GSR is critical in early symbiosis ( 71 ), a group ECF16 σ (EcfS) is required for effective symbiosis in B. diazoefficiens ( 55 ), and ECF σs (EcfF and EcfQ/CarQ) also play a prominent role in the B. diazoefficiens oxidative stress response ( 54 , 72 ).…”

Section: Resultsmentioning

confidence: 99%

“…Like other alphaproteobacteria, S. meliloti lacks an RpoS homolog ( 19 ). Instead, the RpoE2 ECF σ controls a large set of genes related to the general stress response (GSR) ( 20 – 22 ). While RpoN and RpoH1 are dispensable for growth in rich and defined media, they are required for effective symbiosis on Medicago host plants ( 23 – 26 ).…”

Section: Introductionmentioning

confidence: 99%

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MostSinorhizobium melilotiExtracytoplasmic Function Sigma Factors Control Accessory Functions

Lang

Barnett

Fisher

et al. 2018

mSphere

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Fixed (reduced) soil nitrogen plays a critical role in soil fertility and successful food growth. Much soil fertility relies on symbiotic nitrogen fixation: the bacterial partner infects the host plant roots and reduces atmospheric dinitrogen in exchange for host metabolic fuel, a process that involves complex interactions between the partners mediated by changes in gene expression in each partner. Here we test the roles of a family of 11 extracytoplasmic function (ECF) gene regulatory proteins (sigma factors [σs]) that interact with RNA polymerase to determine if they play a significant role in establishing a nitrogen-fixing symbiosis or in responding to various stresses, including cell envelope stress. We discovered that symbiotic nitrogen fixation occurs even when all 11 of these regulatory genes are deleted, that most ECF sigma factors control accessory functions, and that none of the ECF sigma factors are required to survive envelope stress.

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“…The GSR in alphaproteobacteria is mediated by some but not all group ECF15 σs ( 20 , 40 , 41 ). RpoE2 is the GSR σ factor in S. meliloti ( 21 , 42 ).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

MostSinorhizobium melilotiExtracytoplasmic Function Sigma Factors Control Accessory Functions

Lang

Barnett

Fisher

et al. 2018

mSphere

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Salt- and Osmo-Responsive Sensor Histidine Kinases Activate the Bradyrhizobium diazoefficiens General Stress Response to Initiate Functional Symbiosis

Wülser

Ernst

Vetsch

et al. 2022

MPMI

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The general stress response (GSR) enables bacteria to sense and overcome a variety of environmental stresses. In alphaproteobacteria, stress-perceiving histidine kinases of the HWE and HisKA_2 families trigger a signaling cascade that leads to phosphorylation of the response regulator PhyR and consequently to activation of the GSR sigma factor σEcfG. In the nitrogen-fixing bacterium Bradyrhizobium diazoefficiens, PhyR and σEcfG are crucial for tolerance against a variety of stresses under free-living conditions and also for efficient infection of its symbiotic host soybean. However, the molecular players involved in stress perception and activation of the GSR remained largely unknown. In this work, we first showed that a mutant variant of PhyR where the conserved phosphorylatable aspartate residue D194 was replaced by alanine (PhyRD194A) failed to complement the ΔphyR mutant in symbiosis, confirming that PhyR acts as a response regulator. To identify the PhyR-activating kinases in the nitrogen-fixing symbiont, we constructed in-frame deletion mutants lacking single, distinct combinations, or all of the eleven predicted HWE and HisKA_2 kinases, which we named HhkA through HhkK. Phenotypic analysis of the mutants and complemented derivatives identified two functionally redundant kinases, HhkA and HhkE, that are required for nodulation competitiveness and during initiation of symbiosis. Using σEcfG activity reporter strains, we further showed that both HhkA and HhkE activate the GSR in free-living cells exposed to salt and hyperosmotic stress. In conclusion, our data suggest that HhkA and HhkE trigger GSR activation in response to osmotically stressful conditions which B. diazoefficiens encounters during soybean host infection.

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The General Stress Response in Alpha‐Rhizobia

Cited by 2 publications

References 70 publications

MostSinorhizobium melilotiExtracytoplasmic Function Sigma Factors Control Accessory Functions

MostSinorhizobium melilotiExtracytoplasmic Function Sigma Factors Control Accessory Functions

Salt- and Osmo-Responsive Sensor Histidine Kinases Activate the Bradyrhizobium diazoefficiens General Stress Response to Initiate Functional Symbiosis

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