Regulation of exopolysaccharide synthesis in Rhizobium sp. strain TAL1145 involves an alternative sigma factor gene, rpoH2

Kaufusi, Pakieli H.; Forsberg, Lennart S.; Tittabutr, Panlada; Borthakur, Dulal

doi:10.1099/mic.0.27092-0

Cited by 16 publications

(10 citation statements)

References 38 publications

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“…Singlet oxygen and increased temperature are very different phenomena, but in R. sphaeroides the transcriptional responses to these two stresses involve two alternative σ factors, RpoH I and RpoH II , that each belong to the RpoH family [15], [16], [18]. Several other α-proteobacteria contain two or more members of the RpoH family that appear to control different stress responses [13], [29], [30]. However, as it is the case in R. sphaeroides , little is known about the target genes for these multiple RpoH homologs.…”

Section: Discussionmentioning

confidence: 99%

Convergence of the Transcriptional Responses to Heat Shock and Singlet Oxygen Stresses

et al. 2012

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Cells often mount transcriptional responses and activate specific sets of genes in response to stress-inducing signals such as heat or reactive oxygen species. Transcription factors in the RpoH family of bacterial alternative σ factors usually control gene expression during a heat shock response. Interestingly, several α-proteobacteria possess two or more paralogs of RpoH, suggesting some functional distinction. We investigated the target promoters of Rhodobacter sphaeroides RpoHI and RpoHII using genome-scale data derived from gene expression profiling and the direct interactions of each protein with DNA in vivo. We found that the RpoHI and RpoHII regulons have both distinct and overlapping gene sets. We predicted DNA sequence elements that dictate promoter recognition specificity by each RpoH paralog. We found that several bases in the highly conserved TTG in the −35 element are important for activity with both RpoH homologs; that the T-9 position, which is over-represented in the RpoHI promoter sequence logo, is critical for RpoHI–dependent transcription; and that several bases in the predicted −10 element were important for activity with either RpoHII or both RpoH homologs. Genes that are transcribed by both RpoHI and RpoHII are predicted to encode for functions involved in general cell maintenance. The functions specific to the RpoHI regulon are associated with a classic heat shock response, while those specific to RpoHII are associated with the response to the reactive oxygen species, singlet oxygen. We propose that a gene duplication event followed by changes in promoter recognition by RpoHI and RpoHII allowed convergence of the transcriptional responses to heat and singlet oxygen stress in R. sphaeroides and possibly other bacteria.

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Section: Discussionmentioning

confidence: 99%

Convergence of the Transcriptional Responses to Heat Shock and Singlet Oxygen Stresses

et al. 2012

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“…Although the functions of these genes remain elusive, rpoH2 from Rhizobium sp. strain TAL1145 has been involved in exopolysaccharide biosynthesis and nodulation (35), whereas rpoH2 from Sinorhizobium sp. strain BL3 seems to be required for salt stress tolerance (69).…”

Section: Discussionmentioning

confidence: 99%

An Extracytoplasmic Function Sigma Factor Acts as a General Stress Response Regulator inSinorhizobium meliloti

et al. 2007

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Sinorhizobium meliloti genes transcriptionally up-regulated after heat stress, as well as upon entry into stationary phase, were identified by microarray analyses. Sixty stress response genes were thus found to be up-regulated under both conditions. One of them, rpoE2 (smc01506), encodes a putative extracytoplasmic function (ECF) sigma factor. We showed that this sigma factor controls its own transcription and is activated by various stress conditions, including heat and salt, as well as entry into stationary phase after either carbon or nitrogen starvation. We also present evidence that the product of the gene cotranscribed with rpoE2 negatively regulates RpoE2 activity, and we therefore propose that it plays the function of anti-sigma factor. By combining transcriptomic, bioinformatic, and quantitative reverse transcription-PCR analyses, we identified 44 RpoE2-controlled genes and predicted the number of RpoE2 targets to be higher. Strikingly, more than one-third of the 60 stress response genes identified in this study are RpoE2 targets. Interestingly, two genes encoding proteins with known functions in stress responses, namely, katC and rpoH2, as well as a second ECF-encoding gene, rpoE5, were found to be RpoE2 regulated. Altogether, these data suggest that RpoE2 is a major global regulator of the general stress response in S. meliloti. Despite these observations, and although this sigma factor is well conserved among alphaproteobacteria, no in vitro nor in planta phenotypic difference from the wild-type strain could be detected for rpoE2 mutants. This therefore suggests that other important actors in the general stress response have still to be identified in S. meliloti.To survive the many stress conditions that they encounter in nature, bacteria have evolved rapid responses that result in the prevention or repair of cellular damages caused by stresses. In addition to these usually stress-specific responses, more general stress responses take place in reaction to a variety of insults as different as high osmolarity, heat or cold shock, pH variation, and nutrient starvation (which results in stationary phase). One well-known consequence of these general stress responses is the ability of bacteria to resist stress better in stationary phase than in exponential phase. This phenomenon, observed in most bacterial species studied so far, is considered a universal way for these microorganisms to survive not only the stress that they currently experience, but also stress conditions that they could potentially face in the future, and is therefore of primary importance in nature, where bacteria often are nutrient or oxygen limited and where environmental conditions constantly change (28).Much of our knowledge regarding the mechanisms of induction of general stress responses derives from studies of the model bacterium Escherichia coli and its close relatives. In these bacteria, entry into stationary phase, as well as a number of different stress conditions, leads to the activation of alternative sigma factors, which re...

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“…For example, rpoH2 in Rhizobium sp. strain TAL1145 regulates genes for exopolysaccharide synthesis, which is required for effective nodulation (24). Mitsui et al (28) determined whether RpoH1 and RpoH2 control expression of nine HSP homologs in S. meliloti (groESL1 through groESL5, dnaK, clpA, clpB, and lon) during heat shock.…”

Section: Discussionmentioning

confidence: 99%

“…Rhizobium sp. strain TAL1145 has at least one rpoH gene, and the rpoH mutant exhibits reduced nodulation, resulting in stunted plant growth (24). Rhizobium leguminosarum has at least three groESL operons (39,44), and Mesorhizobium loti has two rpoH genes and five groESL operons (22,24).…”

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Multiple groESL Operons Are Not Key Targets of RpoH1 and RpoH2 in Sinorhizobium meliloti

Bittner

Oke

2006

J Bacteriol

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Among the rhizobia that establish nitrogen-fixing nodules on the roots of host plants, many contain multiple copies of genes encoding the sigma factor RpoH and the chaperone GroEL/GroES. In Sinorhizobium meliloti there are two rpoH genes, four groESL operons, and one groEL gene. rpoH1 mutants are defective for growth at high temperature and form ineffective nodules, rpoH1 rpoH2 double mutants are unable to form nodules, and groESL1 mutants form ineffective nodules. To explore the roles of RpoH1 and RpoH2, we identified mutants that suppress both the growth and nodulation defects. These mutants do not suppress the nitrogen fixation defect. This implies that the functions of RpoH1 during growth and RpoH1/RpoH2 during the initiation of symbiosis are similar but that there is a different function of RpoH1 needed later during symbiosis. We showed that, unlike in Escherichia coli, overexpression of groESL is not sufficient to bypass any of the RpoH defects. Under free-living conditions, we determined that RpoH2 does not control expression of the groE genes, and RpoH1 only controls expression of groESL5. Finally, we completed the series of groE mutants by constructing groESL3 and groEL4 mutants and demonstrated that they do not display symbiotic defects. Therefore, the only groESL operon required by itself for symbiosis is groESL1. Taken together, these results suggest that GroEL/ GroES production alone cannot explain the requirements for RpoH1 and RpoH2 in S. meliloti and that there must be other crucial targets.

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Regulation of exopolysaccharide synthesis in Rhizobium sp. strain TAL1145 involves an alternative sigma factor gene, rpoH2

Cited by 16 publications

References 38 publications

Convergence of the Transcriptional Responses to Heat Shock and Singlet Oxygen Stresses

Convergence of the Transcriptional Responses to Heat Shock and Singlet Oxygen Stresses

An Extracytoplasmic Function Sigma Factor Acts as a General Stress Response Regulator inSinorhizobium meliloti

Multiple groESL Operons Are Not Key Targets of RpoH1 and RpoH2 in Sinorhizobium meliloti

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