Stress oxydant | EPFL Graph Search

Le stress oxydant, appelé aussi stress oxydatif (anglicisme) ou pression oxydative, est un type d'agression des constituants de la cellule. Il apparait quand des espèces réactives oxygénées (ou radicaux libres) et/ou des espèces réactives oxygénées et azotées oxydant pénètrent la cellule ou s'y forment ; ces molécules sont instables et très cytotoxiques car elles « oxydent » d'autres molécules en leur soustrayant un électron ce qui les rend à leur tour instables. Ces espèces peuvent être ou non des radicaux. Les trois plus connues sont l'anion superoxyde (O2), le radical hydroxyle (HO) et le peroxyde d'hydrogène () ; ce peroxyde d'hydrogène naturellement produit par le métabolisme cellulaire, en présence de fer (sous forme ionique, fer ferreux Fe2+) produit des radicaux hydroxyle (réaction de Fenton) intracellulaires très toxiques, mais dans une cellule saine il est neutralisé presque en temps réel par du glutathion (qui le transforme en eau)

The NPR1-dependent salicylic acid signalling pathway is pivotal for enhanced salt and oxidative stress tolerance in Arabidopsis

Amandine Massart

The role of endogenous salicylic acid (SA) signalling cascades in plant responses to salt and oxidative stresses is unclear. Arabidopsis SA signalling mutants, namely npr1-5 (non-expresser of pathogenesis related gene1), which lacks NPR1-dependent SA signalling, and nudt7 (nudix hydrolase7), which has both constitutively expressed NPR1-dependent and NPR1-independent SA signalling pathways, were compared with the wild type (Col-0) during salt or oxidative stresses. Growth and viability staining showed that, compared with wild type, the npr1-5 mutant was sensitive to either salt or oxidative stress, whereas the nudt7 mutant was tolerant. Acute salt stress caused the strongest membrane potential depolarization, highest sodium and proton influx, and potassium loss from npr1-5 roots in comparison with the wild type and nudt7 mutant. Though salt stress-induced hydrogen peroxide production was lowest in the npr1-5 mutant, the reactive oxygen species (ROS) stress (induced by 1 mM of hydroxyl-radical-generating copper-ascorbate mix, or either 1 or 10 mM hydrogen peroxide) caused a higher potassium loss from the roots of the npr1-5 mutant than the wild type and nudt7 mutant. Long-term salt exposure resulted in the highest sodium and the lowest potassium concentration in the shoots of npr1-5 mutant in comparison with the wild type and nudt7 mutant. The above results demonstrate that NPR1-dependent SA signalling is pivotal to (i) controlling Na+ entry into the root tissue and its subsequent long-distance transport into the shoot, and (ii) preventing a potassium loss through depolarization-activated outward-rectifying potassium and ROS-activated non-selective cation channels. In conclusion, NPR1-dependent SA signalling is central to the salt and oxidative stress tolerance in Arabidopsis.

Oxford University Press2015

Identification and characterization of proteins that protect human telomeres from fragility

Anna Christina Näger

Difficulties to replicate telomeres - the ends of our chromosomes - can cause telomere shortening andgenome instability. These difficulties are due to the repetitive DNA sequence and distinct structures at telomeresthat challenge the semi-conservative DNA replication machinery. Among the proteins that help toovercome the obstacles to telomere replication are factors known to be mutated in genetic diseases (forinstance WRN, BLM, RTEL1, CTC1), but we suspect that there are still factors and pathways unknown.DNA replication defects at telomeres manifest as smeary or multiple telomeric fluorescence in situ hybridization(FISH) signals on metaphase chromosomes - commonly called telomere fragility. To identify proteinsthat protect human telomeres from fragility, we depleted 71 proteins (including 8 controls) from HeLa cellsusing siRNA pools and analysed their metaphase chromosomes for fragile telomeres. The majority of theseproteins had been identified by QTIP-iPOND - a proteomic analysis of chromatin near telomere replicationforks. Among the 71 proteins that were depleted in the siRNA screen, we identified 29 novel proteins thatprevent telomere fragility and are therefore crucial to maintain genome stability. The telomere fragilityscreen validated QTIP-iPOND as a technique to identify telomere replication proteins. The hits identified inour telomere fragility screen may for example have functions in regulating telomeric chromatin compositionand compaction, regulating transcription of the telomeric long non-coding RNA TERRA and its associationwith telomeric chromatin, dealing with replication stress and stalled replication forks, modulating DNAdamage signalling and repair, modulating sister chromatid cohesion, and preventing oxidative stress.One of the 29 novel proteins identified in the telomere fragility screen is chromobox 8 (CBX8) whose functionat telomeres was investigated in further detail in this study. CBX8 is a component of the canonical polycombrepressive complex 1 (PRC1), an epigenetic regulator of gene expression. However, CBX8 also hasfunctions that are independent of the PRC1 complex. We show that human CBX8 prevents telomere fragilitycaused by RNA-DNA hybrids which could stall replication forks and induce homologous recombination.CBX8 depletion or knockout did however not affect telomeric RNA-DNA hybrid levels. We hypothesize thatCBX8 may be involved in repair activities at stalled replication forks that arise when the replisome encounterspersistent RNA-DNA hybrids. Moreover, we found that CBX8 localizes to telomeric repeat-binding factor2 (TRF2)-deficient telomeres in a manner that is dependent on RNA-DNA hybrids and ATM signalling.We demonstrate that H3K27me3 (trimethylated histone 3 lysine 27) marks, which have previously beensuggested to help recruitment of CBX proteins to chromatin via the CBX chromodomain, are dispensable forCBX8 recruitment to TRF2-deficient telomeres. Furthermore, we found that CBX8 promotes non-homologousend joining (NHEJ)-mediated telomere fusions of dysfunctional telomeres. We therefore hypothesizethat CBX8 is involved in repair activities that influence the DNA repair pathway choice at TRF2-deficient telomeres.

EPFL2022

Reactive oxygen species production and signalling as a component of salinity tolerance mechanism in cereals

Amandine Massart

Reactive Oxygen Species (ROS) are highly reactive and toxic by-products of the aerobic metabolism, which are overproduced during period of stress. They disturb the cell machinery and induce oxidative damages on important biological macromolecules. Salinity is one of those major abiotic stresses, which affects considerably the growth rate and limits crop productivity. To enhance salinity stress tolerance and find strategies which would cope with global issues related to the rise of salt-affected lands and global food demand, various investigations have been performed. They did mainly focus on the understanding of physiological traits and ion homeostasis responses. However, oxidative stress is also a key part of the plant response to stress, but is still under-investigated. An efficient oxidative stress tolerance mechanism may induce significant improvement in salinity resistance. Nevertheless, recent studies have suggested that ROS play a dual role in cells, both as toxic by-products and as key molecules in complex signalling networks: ROS are essential actors which could influence the expression and regulation of various genes to control many processes, including the stress response. In this project, the production of two ROS, hydrogen peroxide and superoxide, was investigated in roots from various species and genotypes, respectively by DCF-DA and DHE fluorescence. The study gave a basic framework about ROS kinetics accumulation in roots depending on time of exposure to different salt concentrations. Specificities related to growth conditions, plant age and root tissues were also investigated. It was demonstrated that, compared to wheat and even more to pea, barley has a better ability to handle salinity, thanks to a rapid and transient oxidative burst. The aim of this work was also to link the oxidative stress with salinity stress tolerance, which had been investigated in previous studies. Two main conclusions can be drawn from this project: (i) there is a clear correlation between ROS accumulation and K+ leaking studied in previous experiments; (ii) ROS have a significant implication in the signal transduction network. Knowledge about the main mechanisms involved in oxidative stress tolerance and signalling can give a better background in the development of plants with improved salinity tolerance and find adapted solutions to this growing concern.

2013

Identification and characterization of proteins that protect human telomeres from fragility

Anna Christina Näger

EPFL2022

Reactive oxygen species production and signalling as a component of salinity tolerance mechanism in cereals

Amandine Massart

2013