Key players of singlet oxygen-induced cell death in plants

International audienceThe production of reactive oxygen species (ROS) is an unavoidable consequence of oxygenic photosynthesis. Singlet oxygen (1 O 2) is a highly reactive species to which has been attributed a major destructive role during the execution of ROS-induced cell death in photosynthetic tissues exposed to excess light. The study of the specific biological activity of 1 O 2 in plants has been hindered by its high reactivity and short lifetime, the concurrent production of other ROS under photooxidative stress, and limited in vivo detection methods. However, during the last 15 years, the isolation and characterization of two 1 O 2-overproducing mutants in Arabidopsis thaliana, flu and ch1, has allowed the identification of genetically controlled 1 O 2 cell death pathways and a 1 O 2 acclimation pathway that are triggered at sub-cytotoxic concentrations of 1 O 2. The study of flu has revealed the control of cell death by the plastid proteins EXECUTER (EX)1 and EX2. In ch1, oxidized derivatives of β-carotene, such as β-cyclocitral and dihydroactinidiolide, have been identified as important upstream messengers in the 1 O 2 signaling pathway that leads to stress acclimation. In both the flu and ch1 mutants, phytohormones act as important promoters or inhibitors of cell death. In particular, jasmonate has emerged as a key player in the decision between acclimation and cell death in response to 1 O 2. Although the flu and ch1 mutants show many similarities, especially regarding their gene expression profiles, key differences, such as EXECUTER-independent cell death in ch1, have also been observed and will need further investigation to be fully understood

A genetic approach towards elucidating the biological activity of different reactive oxygen species in Arabidopsis thaliana

Plants are often exposed to external conditions that adversely affect their growth, development or productivity. Such unfavourable environmental stress factors may result in rapid and transient increases of intracellular concentrations of reactive oxygen species (ROS) that are chemically distinct and impact plants either by being cytotoxic or by acting as a signal. Because different ROS are generated simultaneously in different cellular and extracellular compartments, it is almost impossible to link a particular ROS to a specific stress response and to determine its mode of action. The conditional flu mutant of Arabidopsis has been used to determine the biological role of singlet oxygen. Immediately after a dark/light shift of the flu mutant, singlet oxygen is generated within the plastids activating several stress responses that include growth inhibition of mature plants and seedling lethality. These stress responses do not result from physicochemical damage caused by singlet oxygen, but are attributable to the activation of a genetically determined stress response programme triggered by the Executer1 protein. Singlet oxygen-mediated stress responses at the transcriptional level necessitate a retrograde transduction of signals from the chloroplast to the nucleus that activate distinct sets of genes different from those that are induced by superoxide/hydrogen peroxide. Hence, the biological activities of these two types of ROS are distinct from each other. Whether they act independently or interact is not known yet and is the topic of our current researc

Profiling of sugar transporter genes in grapevine coping with water deficit

AbstractThe profiling of grapevine (Vitis vinifera L.) genes under water deficit was specifically targeted to sugar transporters. Leaf water status was characterized by physiological parameters and soluble sugars content. The expression analysis provided evidence that VvHT1 hexose transporter gene was strongly down-regulated by the increased sugar content under mild water-deficit. The genes of monosaccharide transporter VvHT5, sucrose carrier VvSUC11, vacuolar invertase VvGIN2 and grape ASR (ABA, stress, ripening) were up-regulated under severe water stress. Their regulation in a drought-ABA signalling network and possible roles in complex interdependence between sugar subcellular partitioning and cell influx/efflux under Grapevine acclimation to dehydration are discussed

Arabidopsis mutants reveal multiple singlet oxygen signaling pathways involved in stress response and development

Shortly after the release of singlet oxygen (1O2) in chloroplasts drastic changes in nuclear gene expression occur in the conditional flu mutant of Arabidopsis that reveal a rapid transfer of signals from the plastid to the nucleus. Factors involved in this retrograde signaling were identified by mutagenizing a transgenic flu line expressing a 1O2-responsive reporter gene. The reporter gene consisted of the luciferase open reading frame and the promoter of an AAA-ATPase gene (At3g28580) that was selectively activated by 1O2 but not by superoxide or hydrogen peroxide. A total of eight second-site mutants were identified that either constitutively activate the reporter gene and the endogenous AAA-ATPase irrespectively of whether 1O2 was generated or not (constitutive activators of AAA-ATPase, caa) or abrogated the 1O2-dependent up-regulation of these genes as seen in the transgenic parental flu line (non-activators of AAA-ATPase, naa). The characterization of the mutants strongly suggests that 1O2-signaling does not operate as an isolated linear pathway but rather forms an integral part of a signaling network that is modified by other signaling routes and impacts not only stress responses of plants but also their developmen

Transcriptomic footprints disclose specificity of reactive oxygen species signaling in Arabidopsis

Reactive oxygen species ( ROS) are key players in the regulation of plant development, stress responses, and programmed cell death. Previous studies indicated that depending on the type of ROS ( hydrogen peroxide, superoxide, or singlet oxygen) or its subcellular production site ( plastidic, cytosolic, peroxisomal, or apoplastic), a different physiological, biochemical, and molecular response is provoked. We used transcriptome data generated from ROS-related microarray experiments to assess the specificity of ROS-driven transcript expression. Data sets obtained by exogenous application of oxidative stress-causing agents ( methyl viologen, Alternaria alternata toxin, 3-aminotriazole, and ozone) and from a mutant ( fluorescent) and transgenic plants, in which the activity of an individual antioxidant enzyme was perturbed ( catalase, cytosolic ascorbate peroxidase, and copper/zinc superoxide dismutase), were compared. In total, the abundance of nearly 26,000 transcripts of Arabidopsis ( Arabidopsis thaliana) was monitored in response to different ROS. Overall, 8,056, 5,312, and 3,925 transcripts showed at least a 3-, 4-, or 5- fold change in expression, respectively. In addition to marker transcripts that were specifically regulated by hydrogen peroxide, superoxide, or singlet oxygen, several transcripts were identified as general oxidative stress response markers because their steady-state levels were at least 5- fold elevated in most experiments. We also assessed the expression characteristics of all annotated transcription factors and inferred new candidate regulatory transcripts that could be responsible for orchestrating the specific transcriptomic signatures triggered by different ROS. Our analysis provides a framework that will assist future efforts to address the impact of ROS signals within environmental stress conditions and elucidate the molecular mechanisms of the oxidative stress response in plants

Dissection of the transcriptional regulation of grape ASR and response to glucose and abscisic acid

Despite the fact that the precise physiological function of ASRs [abscisic acid (ABA), stress, ripening] remains unknown, they have been suggested to play a dual role in the plant response to environmental cues, as highly hydrophilic proteins for direct protection, as well as transcription factors involved in the regulation of gene expression. To investigate further the biological positioning of grape ASR in the hormonal and metabolic signal network, three promoters corresponding to its cDNA were isolated and submited to a detailed in silico and functional analysis. The results obtained provided evidence for the allelic polymorphism of the grape ASR gene, the organ-preferential expression conferred on the GUS reporter gene, and the specific phloem tissue localization revealed by in situ hybridization. The study of glucose and ABA signalling in its transcriptional control, by transfection of grape protoplasts using the dual luciferase system, revealed the complexity of ASR gene expression regulation. A model was proposed allowing a discussion of the place of ASR in the fine tuning of hormonal and metabolic signalling involved in the integration of environmental cues by the plant organism

A rare and exclusive endoperoxide photoproduct derived from thiacalix[4]arene crown-shaped derivative bearing 9,10-substituted anthracene moiety

A rare and exclusive endoperoxide photoproduct was quantitatively obtained from a thiacalix[4]arene crown-shaped derivative upon irradiation at λ=365 nm; the structure was unambiguously confirmed by 1H/13C NMR spectroscopy and X-ray crystallography. The prerequisites for the formation of the endoperoxide photoproduct have also been discussed. Furthermore, the photochemical reaction rate could be greatly enhanced in the presence of the thiacalix[4]arene platform because it served as a host to capture oxygen

Hexameric oligomerization of mitochondrial peroxiredoxin PrxIIF and formation of an ultrahigh affinity complex with its electron donor thioredoxin Trx-o

Mitochondria from plants, yeast, and animals each contain at least one peroxiredoxin (Prx) that is involved in peroxide detoxification and redox signalling. The supramolecular dynamics of atypical type II Prx targeted to the mitochondrion was addressed in pea. Microcalorimetric (ITC) titrations identified an extremely high-affinity binding between the mitochondrial PsPrxIIF and Trx-o with a KD of 126±14 pM. Binding was driven by a favourable enthalpy change (ΔH= –60.6 kcal mol−1) which was counterbalanced by unfavourable entropy changes (TΔS= –47.1 kcal mol−1). This is consistent with the occurrence of large conformational changes during binding which was abolished upon site-directed mutaganesis of the catalytic C59S and C84S. The redox-dependent interaction was confirmed by gel filtration of mitochondrial extracts and co-immunoprecipitation from extracts. The heterocomplex of PsPrxIIF and Trx-o reduced peroxide substrates more efficiently than free PsPrxIIF suggesting that Trx-o serves as an efficient and specific electron donor to PsPrxIIF in vivo. Other Trx-s tested by ITC analysis failed to interact with PsPrxIIF indicating a specific recognition of PsPrxIIF by Trx-o. PsPrxIIF exists primarily as a dimer or a hexamer depending on the redox state. In addition to the well-characterized oligomerization of classical 2-Cys Prx the results also show that atypical Prx undergo large structural reorganization with implications for protein–protein interaction and function

Cabergoline therapy for macroprolactinoma during pregnancy: a case report.

Background: We assessed the safety of Cabergoline therapy during pregnancy in a lady with hyperprolactinemia intolerant to Bromocriptine. Case presentation: We report the case of a 31 year old lady who presented to us with uncontrolled hyperprolactinemia. A pituitary Macroadenoma was demonstrated by MRI. Due to intolerance to Bromocriptine, Cabergoline was started. The patient improved and subsequently conceived. MRI in the second trimester demonstrated further reduction in the tumor size. It was decided to continue Cabergoline throughout pregnancy to ensure further reduction in tumor size until delivery and to hold Cabergoline during postpartum period to allow for an adequate interval of breastfeeding. At 37 weeks of gestation, the patient delivered a healthy baby. Conclusion: We were able to safely treat macroprolactinemia in our patient during pregnancy with cabergoline. This case report contributes to the relatively meager data available which advocates the safety of cabergoline therapy in pregnant hyperprolactinemic patients