Miriam Laxa

Bio: Miriam Laxa is an academic researcher from Leibniz University of Hanover. The author has contributed to research in topics: Arabidopsis & Peroxiredoxin. The author has an hindex of 16, co-authored 20 publications receiving 1973 citations. Previous affiliations of Miriam Laxa include University of Oxford & Bielefeld University.

The function of peroxiredoxins in plant organelle redox metabolism

Abstract: In 1996, cDNA sequences referred to as plant peroxiredoxins (Prx), i.e. a 1-Cys Prx and a 2-Cys Prx, were reported from barley. Ten years of research have advanced our understanding of plant Prx as thiol-based peroxide reductases with a broad substrate specificity, ranging from hydrogen peroxide to alkyl hydroperoxides and peroxinitrite. Prx have several features in common. (i) They are abundant proteins that are routinely detected in proteomics approaches. (ii) They interact with proteins such as glutaredoxins, thioredoxins, and cyclophilins as reductants, but also non-dithioldisulphide exchange proteins. By work with transgenic plants, their activity was shown to (iii) affect metabolic integrity, (iv) protect DNA from damage in vitro and as shown here in vivo, and (v) modulate intracellular signalling related to reactive oxygen species and reactive nitrogen species. (vi) In all organisms Prx are encoded by small gene families that are of particular complexity in higher plants. A comparison of the Prx gene families in rice and Arabidopsis thaliana supports previous suggestions on Prx function in specific subcellular and metabolic context. (vii) Prx gene expression and activity are subjected to complex regulation realized by an integration of various signalling pathways. 2-Cys Prx expression depends on redox signals, abscisic acid, and protein kinase cascades. Besides these general properties, the chloroplast Prx have acquired specific roles in the context of photosynthesis. The thioredoxin-dependent peroxidase activity can be measured in crude plant extracts and contributes significantly to the overall H2O2 detoxification capacity. Thus organellar Prx proteins enable an alternative water–water cycle for detoxification of photochemically produced H2O2, which acts independently from the ascorbatedependent Asada–Halliwell–Foyer cycle. 2-Cys Prx and Prx Q associate with thylakoid membrane components. The mitochondrial PrxII F is essential for root growth under stress. Following a more general introduction, the paper summarizes present knowledge on plant organellar Prx, addressing Prx in signalling, and also suggests some lines for future research.

The Role of the Plant Antioxidant System in Drought Tolerance.

Abstract: Water deficiency compromises plant performance and yield in many habitats and in agriculture. In addition to survival of the acute drought stress period which depends on plant-genotype-specific characteristics, stress intensity and duration, also the speed and efficiency of recovery determine plant performance. Drought-induced deregulation of metabolism enhances generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which in turn affect the redox regulatory state of the cell. Strong correlative and analytical evidence assigns a major role in drought tolerance to the redox regulatory and antioxidant system. This review compiles current knowledge on the response and function of superoxide, hydrogen peroxide and nitric oxide under drought stress in various species and drought stress regimes. The meta-analysis of reported changes in transcript and protein amounts, and activities of components of the antioxidant and redox network support the tentative conclusion that drought tolerance is more tightly linked to up-regulated ascorbate-dependent antioxidant activity than to the response of the thiol-redox regulatory network. The significance of the antioxidant system in surviving severe phases of dehydration is further supported by the strong antioxidant system usually encountered in resurrection plants.

S-Nitrosylation of Peroxiredoxin II E Promotes Peroxynitrite-Mediated Tyrosine Nitration

Abstract: Nitric oxide (NO) is a free radical product of cell metabolism that plays diverse and important roles in the regulation of cellular function. S-Nitrosylation is emerging as a specific and fundamental posttranslational protein modification for the transduction of NO bioactivity, but very little is known about its physiological functions in plants. We investigated the molecular mechanism for S-nitrosylation of peroxiredoxin II E (PrxII E) from Arabidopsis thaliana and found that this posttranslational modification inhibits the hydroperoxide-reducing peroxidase activity of PrxII E, thus revealing a novel regulatory mechanism for peroxiredoxins. Furthermore, we obtained biochemical and genetic evidence that PrxII E functions in detoxifying peroxynitrite (ONOO−), a potent oxidizing and nitrating species formed in a diffusion-limited reaction between NO and O2− that can interfere with Tyr kinase signaling through the nitration of Tyr residues. S-Nitrosylation also inhibits the ONOO− detoxification activity of PrxII E, causing a dramatic increase of ONOO−-dependent nitrotyrosine residue formation. The same increase was observed in a prxII E mutant line after exposure to ONOO−, indicating that the PrxII E modulation of ONOO− bioactivity is biologically relevant. We conclude that NO regulates the effects of its own radicals through the S-nitrosylation of crucial components of the antioxidant defense system that function as common triggers for reactive oxygen species– and NO-mediated signaling events.

Proteins of Diverse Function and Subcellular Location Are Lysine Acetylated in Arabidopsis

Abstract: Acetylation of the e-amino group of lysine (Lys) is a reversible posttranslational modification recently discovered to be widespread, occurring on proteins outside the nucleus, in most subcellular locations in mammalian cells. Almost nothing is known about this modification in plants beyond the well-studied acetylation of histone proteins in the nucleus. Here, we report that Lys acetylation in plants also occurs on organellar and cytosolic proteins. We identified 91 Lys-acetylated sites on 74 proteins of diverse functional classes. Furthermore, our study suggests that Lys acetylation may be an important posttranslational modification in the chloroplast, since four Calvin cycle enzymes were acetylated. The plastid-encoded large subunit of Rubisco stands out because of the large number of acetylated sites occurring at important Lys residues that are involved in Rubisco tertiary structure formation and catalytic function. Using the human recombinant deacetylase sirtuin 3, it was demonstrated that Lys deacetylation significantly affects Rubisco activity as well as the activities of other central metabolic enzymes, such as the Calvin cycle enzyme phosphoglycerate kinase, the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase, and the tricarboxylic acid cycle enzyme malate dehydrogenase. Our results demonstrate that Lys acetylation also occurs on proteins outside the nucleus in Arabidopsis (Arabidopsis thaliana) and that Lys acetylation could be important in the regulation of key metabolic enzymes.

Peroxiredoxin Q of Arabidopsis thaliana is attached to the thylakoids and functions in context of photosynthesis.

Abstract: Peroxiredoxin Q (Prx Q) is one out of 10 peroxiredoxins encoded in the genome of Arabidopsis thaliana, and one out of four that are targeted to plastids. Peroxiredoxin Q functions as a monomeric protein and represents about 0.3% of chloroplast proteins. It attaches to the thylakoid membrane and is detected in preparations enriched in photosystem II complexes. Peroxiredoxin Q decomposes peroxides using thioredoxin as an electron donor with a substrate preference of H(2)O(2) > cumene hydroperoxide >> butyl hydroperoxide >> linoleoyl hydroperoxide and insignificant affinity towards complex phospholipid hydroperoxide. Plants with decreased levels of Prx Q did not have an apparently different phenotype from wildtype at the plant level. However, similar to antisense 2-cysteine (2-Cys) Prx plants [Baier, M. et al. (2000)Plant Physiol., 124, 823-832], Prx Q-deficient plants had a decreased sensitivity to oxidants in a leaf slice test as indicated by chlorophyll a fluorescence measurements. Increased fluorescence ratios of photosystem II to I at 77 K and modified transcript levels of plastid- and nuclear-encoded proteins show that regulatory mechanisms are at work to compensate for the lack of Prx Q. Apparently Prx Q attaches to photosystem II and has a specific function distinct from 2-Cys peroxiredoxin in protecting photosynthesis. Its absence causes metabolic changes that are sensed and trigger appropriate compensatory responses.

Reactive oxygen species homeostasis and signalling during drought and salinity stresses

Abstract: Water deficit and salinity, especially under high light intensity or in combination with other stresses, disrupt photosynthesis and increase photorespiration, altering the normal homeostasis of cells and cause an increased production of reactive oxygen species (ROS). ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules. In this review, we provide an overview of ROS homeostasis and signalling in response to drought and salt stresses and discuss the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses.

Production and scavenging of reactive oxygen species in chloroplasts and their functions.

Abstract: The reaction centers of PSI and PSII in chloroplast thylakoids are the major generation site of reactive oxygen species (ROS). Photoreduction of oxygen to hydrogen peroxide (H2O2) in PSI was discovered over 50 years ago by [Mehler (1951)][1]. Subsequently, the primary reduced product was identified

Ascorbate and glutathione: the heart of the redox hub.

Abstract: The discovery that there is a close relationship between ascorbate and glutathione dates from soon after the characterization of the chemical formulae of the two molecules ([Szent-Gyorgyi, 1931][1]; [Hopkins and Morgan, 1936][2]). Similarly, it has long been known that thylakoids can generate

Oxidative Modifications to Cellular Components in Plants

Abstract: Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are produced in many places in living cells and at an increased rate during biotic or abiotic stress. ROS and RNS participate in signal transduction, but also modify cellular components and cause dam- age. We first look at the most common ROS and their properties. We then consider the ways in which the cell can regulate their pro- duction and removal. We critically assess current knowledge about modifications of polyunsaturated fatty acids (PUFAs), DNA, carbo- hydrates, and proteins and illustrate this knowledge with case stories wherever possible. Some oxidative breakdown products, e.g., from PUFA, can cause secondary damage. Other oxidation products are secondary signaling molecules. We consider the fate of the modi- fied components, the energetic costs to the cell of replacing such components, as well as strategies to minimize transfer of oxidatively damaged components to the next generation.