Papers by Gwenola Gouesbet
Frontiers in Plant Science, 2015
Lolium perenne, which is a major component of pastures, lawns, and grass strips, can be exposed t... more Lolium perenne, which is a major component of pastures, lawns, and grass strips, can be exposed to xenobiotic stresses due to diffuse and residual contaminations of soil. L. perenne was recently shown to undergo metabolic adjustments in response to sub-toxic levels of xenobiotics. To gain insight in such chemical stress responses, a de novo transcriptome analysis was carried out on leaves from plants subjected at the root level to low levels of xenobiotics, glyphosate, tebuconazole, and a combination of the two, leading to no adverse physiological effect. Chemical treatments influenced significantly the relative proportions of functional categories and of transcripts related to carbohydrate processes, to signaling, to protein-kinase cascades, such as Serine/Threonine-protein kinases, to transcriptional regulations, to responses to abiotic or biotic stimuli and to responses to phytohormones. Transcriptomics-based expressions of genes encoding different types of SNF1 (sucrose non-fermenting 1)-related kinases involved in sugar and stress signaling or encoding key metabolic enzymes were in line with specific qRT-PCR analysis or with the important metabolic and regulatory changes revealed by metabolomic analysis. The effects of pesticide treatments on metabolites and gene expression strongly suggest that pesticides at low levels, as single molecule or as mixture, affect cell signaling and functioning even in the absence of major physiological impact. This global analysis of L. perenne therefore highlighted the interactions between molecular regulation of responses to xenobiotics, and also carbohydrate dynamics, energy dysfunction, phytohormones and calcium signaling.
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Applied and Environmental Microbiology, 2002
The response of Lactobacillus delbrueckii subsp. bulgaricus cells to heat stress was studied by u... more The response of Lactobacillus delbrueckii subsp. bulgaricus cells to heat stress was studied by use of a chemically defined medium. Two-dimensional electrophoresis (2-DE) analysis was used to correlate the kinetics of heat shock protein (HSP) induction with cell recovery from heat injury. We demonstrated that enhanced viability, observed after 10 min at 65°C, resulted from the overexpression of HSP and from mechanisms not linked to protein synthesis. In order to analyze the thermoadaptation mechanisms involved, thermoresistant variants were selected. These variants showed enhanced constitutive tolerance toward heat shock. However, contrary to the wild-type strain, these variants were poorly protected after osmotic or heat pretreatments. This result suggests that above a certain threshold, cells reach a maximum level of protection that cannot be easily exceeded. A comparison of protein patterns showed that the variants were able to induce more rapidly their adaptive mechanisms than the original strain. In particular, the variants were able to express constitutively more HSP, leading to the higher level of thermoprotection observed. This is the first report of the study by 2-DE of the heat stress response in L. delbrueckii subsp. bulgaricus.
Molecular Microbiology, 2002
Mechanosensitive channels play an essential role in the regulation of turgor pressure in bacteria... more Mechanosensitive channels play an essential role in the regulation of turgor pressure in bacteria. In Escherichia coli, there are multiple mechanosensitive channels that have been characterized genetically: MscL, YggB and KefA. In this report, we describe the cloning of the kefA gene, the organization of the KefA protein and the phenotype of a missense mutation, kefA, which affects the KefA mechanosensitive channel. The altered function of the channel is manifest through increased sensitivity to K+ during growth at low osmolarity and complete inhibition of growth in media containing high K+ concentrations (0.6 M) in the presence of betaine or proline. Growth in high Na+ medium (0.6 M NaCl plus 20 mM K+) is normal. Analysis of the cytoplasmic pools shows that the mutant cannot regulate the K+ content of the cytoplasm when grown in high K+ medium. However, regulation of pools of amino acids is essentially normal and the mutant can accumulate high pools of proline during growth inhibition. The mutant shows increased sensitivity to acid hypo-osmotic shock (transition from neutral to acid pH combined with a reduction in osmolarity). The data are consistent with abnormal regulation of KefA in the presence of high K+ concentrations and either betaine or proline.
Journal of Bacteriology
The influence of the osmolarity of the growth medium on anaerobic fermentation and nitrate respir... more The influence of the osmolarity of the growth medium on anaerobic fermentation and nitrate respiratory pathways was analyzed. The levels of several enzymes, including formate dehydrogenase, hydrogenase, and nitrate reductase, plus a nickel uptake system were examined, as was the expression of the corresponding structural and regulatory genes. While some functions appear to be only moderately affected by an increase in osmolarity, others were found to vary considerably. An increase in the osmolarity of the medium inhibits both fermentation and anaerobic respiratory pathways, though in a more dramatic fashion for the former. fnr expression is affected by osmolarity, but the repression of anaerobic gene expression was shown to be independent of FNR regulatory protein, at least for hyd-17 andfdhF. This repression could be mediated by the intracellular concentration of potassium and is reversed by glycine betaine.
Journal of Bacteriology
After having shown that ectoine (a tetrahydropyrimidine) displays osmoprotective properties towar... more After having shown that ectoine (a tetrahydropyrimidine) displays osmoprotective properties towards Escherichia coli (M. Jebbar, R. Talibart, K. Gloux, T. Bernard, and Blanco, J. Bacteriol. 174:5027-5035, 1992), we have investigated the involvement of this molecule in the osmotic adaptation of Rhizobium meliloti. Ectoine appeared almost as effective as glycine betaine in improving the growth of R. meliloti under adverse osmotic conditions (0.5 M NaCl). Moreover, improvement of growth of rhizobial strains insensitive to glycine betaine was also observed. Ectoine transport proved inducible, periplasmic protein dependent, and, as shown by competition experiments, distinct from the transport of glycine betaine. Medium osmolarity had little effect on the uptake characteristics, since the rate of influx increased from 12 to only 20 nmol min-1 mg of protein-1 when NaCl concentrations were raised from 0 to 0.3 or 0.5 M, with a constant of transport of 80 microM. Natural-abundance 13C-nuclea...
Journal of Bacteriology
Growth of Erwinia chrysanthemi in media of elevated osmolarity can be achieved by the uptake and ... more Growth of Erwinia chrysanthemi in media of elevated osmolarity can be achieved by the uptake and accumulation of various osmoprotectants. This study deals with the cloning and sequencing of the ousA gene-encoded osmoprotectant uptake system A from E. chrysanthemi 3937. OusA belongs to the superfamily of solute ion cotransporters. This osmotically inducible system allows the uptake of glycine betaine, proline, ectoine, and pipecolic acid and presents strong similarities in nucleotide sequence and protein function with the proline/betaine porter of Escherichia coli encoded by proP. The control of ousA expression is clearly different from that of proP. It is induced by osmotic strength and repressed by osmoprotectants. Its expression in E. coli is controlled by H-NS and is rpoS dependent in the exponential phase but unaffected by the stationary phase.
Procedia Environmental Sciences, 2015
Conclusion Starch and starch synthesis activity are important integrators of plant growth (Sulmon... more Conclusion Starch and starch synthesis activity are important integrators of plant growth (Sulmon et al, 2011, PLoS ONE 6: e26855; Mugford et al, 2014, Plant Physiol 166: 1733). The phenotypic traits of high sucrose and high starch are reminiscent of mutations affecting circadian clock components, as in the case of the gigantea mutant. All of this suggests that promoter structures of genes involved in AGPase regulation should be further investigated for discovering molecular markers of improved growth and photosynthesis. However, there is still a long way to go in order to obtain a detailed and exhaustive view of starch synthesis regulations in crop species and to envisage transferability to crop species or (Tuncel & Okita, 2011, Plant Sci 211: 52).
Atrazine is a widely used triazine herbicide and has been detected as a contaminant of surface an... more Atrazine is a widely used triazine herbicide and has been detected as a contaminant of surface and ground waters. This photosynthesis inhibitor binds to the D1 protein of photosystem II. This results in inhibition of photosynthetic electron flow and production of triplet chlorophyll and singlet oxygen which generate oxidative stress and possibly apoptosis, thus leading to bleaching and death of plantlets. Atrazine tolerance in plants is often related to genetic mutation of the psbA gene which encodes the D1 protein, or to activation of detoxification pathways. Exogenous sucrose, and to a lesser extent glucose, was shown to confer a high level of atrazine tolerance to wild-type Arabidopsis seedlings. Sugar-treated plants were able to maintain D1 protein level, photosystem II activity and phototrophic growth in the presence of normally lethal atrazine concentrations. This sugar-induced atrazine tolerance was not due to photoheterotrophic growth or to modification of plant development....
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Papers by Gwenola Gouesbet