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Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli.

ABSTRACT: BACKGROUND: The alarmone (p)ppGpp mediates a global reprogramming of gene expression upon nutrient limitation and other stresses to cope with these unfavorable conditions. Synthesis of (p)ppGpp is, in most bacteria, controlled by RelA/SpoT (Rsh) proteins. The role of (p)ppGpp has been characterized primarily in Escherichia coli and several Gram-positive bacteria. Here, we report the first in-depth analysis of the (p)ppGpp-regulon in an ?-proteobacterium using a high-resolution tiling array to better understand the pleiotropic stress phenotype of a relA/rsh mutant. RESULTS: We compared gene expression of the Rhizobium etli wild type and rsh (previously rel) mutant during exponential and stationary phase, identifying numerous (p)ppGpp targets, including small non-coding RNAs. The majority of the 834 (p)ppGpp-dependent genes were detected during stationary phase. Unexpectedly, 223 genes were expressed (p)ppGpp-dependently during early exponential phase, indicating the hitherto unrecognized importance of (p)ppGpp during active growth. Furthermore, we identified two (p)ppGpp-dependent key regulators for survival during heat and oxidative stress and one regulator putatively involved in metabolic adaptation, namely extracytoplasmic function sigma factor EcfG2/PF00052, transcription factor CH00371, and serine protein kinase PrkA. CONCLUSIONS: The regulatory role of (p)ppGpp in R. etli stress adaptation is far-reaching in redirecting gene expression during all growth phases. Genome-wide transcriptome analysis of a strain deficient in a global regulator, and exhibiting a pleiotropic phenotype, enables the identification of more specific regulators that control genes associated with a subset of stress phenotypes. This work is an important step toward a full understanding of the regulatory network underlying stress responses in ?-proteobacteria.

SUBMITTER: Vercruysse M

PROVIDER: S-EPMC3188799 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli.

Vercruysse Maarten M Fauvart Maarten M Jans Ann A Beullens Serge S Braeken Kristien K Cloots Lore L Engelen Kristof K Marchal Kathleen K Michiels Jan J

Genome biology 20110216 2

<h4>Background</h4>The alarmone (p)ppGpp mediates a global reprogramming of gene expression upon nutrient limitation and other stresses to cope with these unfavorable conditions. Synthesis of (p)ppGpp is, in most bacteria, controlled by RelA/SpoT (Rsh) proteins. The role of (p)ppGpp has been characterized primarily in Escherichia coli and several Gram-positive bacteria. Here, we report the first in-depth analysis of the (p)ppGpp-regulon in an α-proteobacterium using a high-resolution tiling arra ...[more]

PMID: 21324192

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Project description:A core component of the α-proteobacterial general stress response is the extracytoplasmic function (ECF) sigma factor EcfG, exclusively present in this taxonomic class. Half of the completed α-proteobacterial genome sequences contain two or more copies of genes encoding σEcfG-like sigma factors, with the primary copy typically located adjacent to genes coding for a cognate anti-sigma factor (NepR) and two-component response regulator (PhyR). So far, the widespread occurrence of additional, non-canonical σEcfG copies has not satisfactorily been explained. This work explores the hierarchical relation between Rhizobium etli σEcfG1 and σEcfG2, canonical and non-canonical σEcfG proteins, respectively. Contrary to reports in other species, we find that σEcfG1 and σEcfG2 act in parallel, as nodes of a complex regulatory network, rather than in series, as elements of a linear regulatory cascade. We demonstrate that both sigma factors control unique yet also shared target genes, corroborating phenotypic evidence. σEcfG1 drives expression of rpoH2, explaining the increased heat sensitivity of an ecfG1 mutant, while katG is under control of σEcfG2, accounting for reduced oxidative stress resistance of an ecfG2 mutant. We also identify non-coding RNA genes as novel σEcfG targets. We propose a modified model for general stress response regulation in R. etli, in which σEcfG1 and σEcfG2 function largely independently. Based on a phylogenetic analysis and considering the prevalence of α-proteobacterial genomes with multiple σEcfG copies, this model may also be applicable to numerous other species. In this study, we investigate to which degree R. etli EcfG1 and EcfG2 regulation is interdependent. Furthermore, we demonstrate that both sigma factors control distinct regulons and pinpoint unique EcfG2 target genes. We also identify non-coding RNAs (ncRNAs) as novel targets of EcfG1 and EcfG2 and show that expression of at least one of these ncRNAs is under direct EcfG control. The presence of ncRNAs in the regulon of an EcfG type sigma factor has not been described previously and adds an extra level of complexity to the regulation of the general stress response in Alpha-proteobacteria. Moreover, considering the widespread existence of Alpha-proteobacterial genomes with multiple EcfG copies, the here presented results not only lead to a better understanding of the general stress response in R. etli, but also contribute to a conceptual paradigm for general stress response regulation by multiple EcfG proteins in Alpha-proteobacteria.

Project description:A core component of the M-NM-1-proteobacterial general stress response is the extracytoplasmic function (ECF) sigma factor EcfG, exclusively present in this taxonomic class. Half of the completed M-NM-1-proteobacterial genome sequences contain two or more copies of genes encoding M-OM-^CEcfG-like sigma factors, with the primary copy typically located adjacent to genes coding for a cognate anti-sigma factor (NepR) and two-component response regulator (PhyR). So far, the widespread occurrence of additional, non-canonical M-OM-^CEcfG copies has not satisfactorily been explained. This work explores the hierarchical relation between Rhizobium etli M-OM-^CEcfG1 and M-OM-^CEcfG2, canonical and non-canonical M-OM-^CEcfG proteins, respectively. Contrary to reports in other species, we find that M-OM-^CEcfG1 and M-OM-^CEcfG2 act in parallel, as nodes of a complex regulatory network, rather than in series, as elements of a linear regulatory cascade. We demonstrate that both sigma factors control unique yet also shared target genes, corroborating phenotypic evidence. M-OM-^CEcfG1 drives expression of rpoH2, explaining the increased heat sensitivity of an ecfG1 mutant, while katG is under control of M-OM-^CEcfG2, accounting for reduced oxidative stress resistance of an ecfG2 mutant. We also identify non-coding RNA genes as novel M-OM-^CEcfG targets. We propose a modified model for general stress response regulation in R. etli, in which M-OM-^CEcfG1 and M-OM-^CEcfG2 function largely independently. Based on a phylogenetic analysis and considering the prevalence of M-NM-1-proteobacterial genomes with multiple M-OM-^CEcfG copies, this model may also be applicable to numerous other species. In this study, we investigate to which degree R. etli EcfG1 and EcfG2 regulation is interdependent. Furthermore, we demonstrate that both sigma factors control distinct regulons and pinpoint unique EcfG2 target genes. We also identify non-coding RNAs (ncRNAs) as novel targets of EcfG1 and EcfG2 and show that expression of at least one of these ncRNAs is under direct EcfG control. The presence of ncRNAs in the regulon of an EcfG type sigma factor has not been described previously and adds an extra level of complexity to the regulation of the general stress response in Alpha-proteobacteria. Moreover, considering the widespread existence of Alpha-proteobacterial genomes with multiple EcfG copies, the here presented results not only lead to a better understanding of the general stress response in R. etli, but also contribute to a conceptual paradigm for general stress response regulation by multiple EcfG proteins in Alpha-proteobacteria. Comparative transcriptome analyses were carried out on four samples: the parental strain (WT) and mutants in either sigma factor gene ecfG1, sigma factor gene ecfG2, and both genes combined.

Dataset Information

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli.

Publications

Stress response regulators identified through genome-wide transcriptome analysis of the (p)ppGpp-dependent response in Rhizobium etli.

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