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Stefan Hortensteiner - One of the best experts on this subject based on the ideXlab platform.
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Pheophorbide a may regulate jasmonate signaling during dark induced senescence
Plant Physiology, 2020Co-Authors: Sylvain Aubry, Niklaus Fankhauser, Serguei Ovinnikov, Adriana Pružinska, Marina Stirnemann, Krzysztof Zienkiewicz, Cornelia Herrfurth, Ivo Feussner, Stefan HortensteinerAbstract:Chlorophyll degradation is one of the most visible signs of leaf senescence. During senescence, chlorophyll is degraded in the multistep Pheophorbide a oxygenase (PAO)/phyllobilin pathway. This pathway is tightly regulated at the transcriptional level, allowing coordinated and efficient remobilization of nitrogen toward sink organs. Using a combination of transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis (Arabidopsis thaliana) mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. Pheophorbide a Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, a mutant deficient in PAO. We propose that Pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and a unique pathway "bottleneck," has been recruited as a signaling molecule of chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a result of senescence, and proposes that the flux of Pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves.
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Pheophorbide a a chlorophyll catabolite may regulate jasmonate signalling during dark induced senescence in arabidopsis
bioRxiv, 2018Co-Authors: Sylvain Aubry, Niklaus Fankhauser, Serguei Ovinnikov, Krzysztof Zienkiewicz, Ivo Feussner, Stefan HortensteinerAbstract:ABSTRACT Chlorophyll degradation is one of the most visible landmarks of leaf senescence. During senescence, chlorophyll is degraded in the multi-step Pheophorbide a oxygenase (PAO)/phyllobilin pathway, which is tightly regulated at the transcriptional level. This regulation allows a coordinated and efficient remobilisation of nitrogen towards sink organs. Taking advantage of combined transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis thaliana mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. Pheophorbide a. Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, deficient in PAO. We propose that Pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and unique pathway ‘bottleneck’, has been recruited as a signalling molecule of the chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a senescence output, but propose that the flux of Pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves. Summary Transcriptome and metabolite profiles of key chlorophyll breakdown mutants reveal complex interplay between speed of chlorophyll degradation and jasmonic acid signalling Financial sources This work was supported by the European Union (Plant Fellow program), the Swiss National Foundation/ERA-NET (grant N° 163504) and the German Research Foundation (DFG, grant N° INST 186/822-1).
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Characterization of the Pheophorbide a oxygenase/phyllobilin pathway of chlorophyll breakdown in grasses
Planta, 2018Co-Authors: Aditi Das, Bastien Christ, Stefan HortensteinerAbstract:Main conclusion Although the PAO/phyllobilin pathway of chlorophyll breakdown is active in grass leaf senescence, the abundance of phyllobilins is far below the amount of degraded chlorophyll. Abstract The yellowing of fully developed leaves is the most prominent visual symptom of plant senescence. Thereby, chlorophyll is degraded via the so-called Pheophorbide a oxygenase (PAO)/phyllobilin pathway to a species-specific set of phyllobilins, linear tetrapyrrolic products of chlorophyll breakdown. Here, we investigated the diversity and abundance of phyllobilins in cereal and forage crops, i.e. barley, rice, ryegrass, sorghum and wheat, using liquid chromatography–mass spectrometry. A total of thirteen phyllobilins were identified, among them four novel, not yet described ones, pointing to a rather high diversity of phyllobilin-modifying activities present in the Gramineae. Along with these phyllobilins, barley orthologs of known Arabidopsis thaliana chlorophyll catabolic enzymes were demonstrated to localize in the chloroplast, and two of them, i.e. PAO and pheophytin Pheophorbide hydrolase, complemented respective Arabidopsis mutants. These data confirm functionality of the PAO/phyllobilin pathway in grasses. Interestingly, when comparing phyllobilin abundance with amounts of degraded chlorophyll in senescent leaves, in most analyzed grass species only minor fractions of chlorophyll were recovered as phyllobilins, opposite to A. thaliana where phyllobilin quantities match degraded chlorophyll rather well. These data show that, despite the presence and activity of the PAO/phyllobilin pathway in barley (and other cereals), phyllobilins do not accumulate stoichiometrically, implying possible degradation of chlorophyll beyond the phyllobilin level.
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characterization of the Pheophorbide a oxygenase phyllobilin pathway of chlorophyll breakdown in grasses
Planta, 2018Co-Authors: Aditi Das, Bastien Christ, Stefan HortensteinerAbstract:Although the PAO/phyllobilin pathway of chlorophyll breakdown is active in grass leaf senescence, the abundance of phyllobilins is far below the amount of degraded chlorophyll. The yellowing of fully developed leaves is the most prominent visual symptom of plant senescence. Thereby, chlorophyll is degraded via the so-called Pheophorbide a oxygenase (PAO)/phyllobilin pathway to a species-specific set of phyllobilins, linear tetrapyrrolic products of chlorophyll breakdown. Here, we investigated the diversity and abundance of phyllobilins in cereal and forage crops, i.e. barley, rice, ryegrass, sorghum and wheat, using liquid chromatography–mass spectrometry. A total of thirteen phyllobilins were identified, among them four novel, not yet described ones, pointing to a rather high diversity of phyllobilin-modifying activities present in the Gramineae. Along with these phyllobilins, barley orthologs of known Arabidopsis thaliana chlorophyll catabolic enzymes were demonstrated to localize in the chloroplast, and two of them, i.e. PAO and pheophytin Pheophorbide hydrolase, complemented respective Arabidopsis mutants. These data confirm functionality of the PAO/phyllobilin pathway in grasses. Interestingly, when comparing phyllobilin abundance with amounts of degraded chlorophyll in senescent leaves, in most analyzed grass species only minor fractions of chlorophyll were recovered as phyllobilins, opposite to A. thaliana where phyllobilin quantities match degraded chlorophyll rather well. These data show that, despite the presence and activity of the PAO/phyllobilin pathway in barley (and other cereals), phyllobilins do not accumulate stoichiometrically, implying possible degradation of chlorophyll beyond the phyllobilin level.
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chlorophyll breakdown in higher plants
Biochimica et Biophysica Acta, 2011Co-Authors: Stefan Hortensteiner, Bernhard KrautlerAbstract:Chlorophyll breakdown is an important catabolic process of leaf senescence and fruit ripening. Structure elucidation of colorless linear tetrapyrroles as (final) breakdown products of chlorophyll was crucial for the recent delineation of a chlorophyll breakdown pathway which is highly conserved in land plants. Pheophorbide a oxygenase is the key enzyme responsible for opening of the chlorin macrocycle of Pheophorbide a characteristic to all further breakdown products. Degradation of chlorophyll was rationalized by the need of a senescing cell to detoxify the potentially phototoxic pigment, yet recent investigations in leaves and fruits indicate that chlorophyll catabolites could have physiological roles. This review updates structural information of chlorophyll catabolites and the biochemical reactions involved in their formation, and discusses the significance of chlorophyll breakdown. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.
Sylvain Aubry - One of the best experts on this subject based on the ideXlab platform.
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Pheophorbide a may regulate jasmonate signaling during dark induced senescence
Plant Physiology, 2020Co-Authors: Sylvain Aubry, Niklaus Fankhauser, Serguei Ovinnikov, Adriana Pružinska, Marina Stirnemann, Krzysztof Zienkiewicz, Cornelia Herrfurth, Ivo Feussner, Stefan HortensteinerAbstract:Chlorophyll degradation is one of the most visible signs of leaf senescence. During senescence, chlorophyll is degraded in the multistep Pheophorbide a oxygenase (PAO)/phyllobilin pathway. This pathway is tightly regulated at the transcriptional level, allowing coordinated and efficient remobilization of nitrogen toward sink organs. Using a combination of transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis (Arabidopsis thaliana) mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. Pheophorbide a Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, a mutant deficient in PAO. We propose that Pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and a unique pathway "bottleneck," has been recruited as a signaling molecule of chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a result of senescence, and proposes that the flux of Pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves.
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Pheophorbide a a chlorophyll catabolite may regulate jasmonate signalling during dark induced senescence in arabidopsis
bioRxiv, 2018Co-Authors: Sylvain Aubry, Niklaus Fankhauser, Serguei Ovinnikov, Krzysztof Zienkiewicz, Ivo Feussner, Stefan HortensteinerAbstract:ABSTRACT Chlorophyll degradation is one of the most visible landmarks of leaf senescence. During senescence, chlorophyll is degraded in the multi-step Pheophorbide a oxygenase (PAO)/phyllobilin pathway, which is tightly regulated at the transcriptional level. This regulation allows a coordinated and efficient remobilisation of nitrogen towards sink organs. Taking advantage of combined transcriptome and metabolite analyses during dark-induced senescence of Arabidopsis thaliana mutants deficient in key steps of the PAO/phyllobilin pathway, we show an unanticipated role for one of the pathway intermediates, i.e. Pheophorbide a. Both jasmonic acid-related gene expression and jasmonic acid precursors specifically accumulated in pao1, deficient in PAO. We propose that Pheophorbide a, the last intact porphyrin intermediate of chlorophyll degradation and unique pathway ‘bottleneck’, has been recruited as a signalling molecule of the chloroplast metabolic status. Our work challenges the assumption that chlorophyll breakdown is merely a senescence output, but propose that the flux of Pheophorbide a through the pathway acts in a feed-forward loop that remodels the nuclear transcriptome and controls the pace of chlorophyll degradation in senescing leaves. Summary Transcriptome and metabolite profiles of key chlorophyll breakdown mutants reveal complex interplay between speed of chlorophyll degradation and jasmonic acid signalling Financial sources This work was supported by the European Union (Plant Fellow program), the Swiss National Foundation/ERA-NET (grant N° 163504) and the German Research Foundation (DFG, grant N° INST 186/822-1).
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pheophytin Pheophorbide hydrolase pheophytinase is involved in chlorophyll breakdown during leaf senescence in arabidopsis
The Plant Cell, 2009Co-Authors: Silvia Schelbert, Sylvain Aubry, Bo Burla, Birgit Agne, Felix Kessler, Karin Krupinska, Stefan HortensteinerAbstract:During leaf senescence, chlorophyll is removed from thylakoid membranes and converted in a multistep pathway to colorless breakdown products that are stored in vacuoles. Dephytylation, an early step of this pathway, increases water solubility of the breakdown products. It is widely accepted that chlorophyll is converted into Pheophorbide via chlorophyllide. However, chlorophyllase, which converts chlorophyll to chlorophyllide, was found not to be essential for dephytylation in Arabidopsis thaliana. Here, we identify pheophytinase (PPH), a chloroplast-located and senescence-induced hydrolase widely distributed in algae and land plants. In vitro, Arabidopsis PPH specifically dephytylates the Mg-free chlorophyll pigment, pheophytin (phein), yielding Pheophorbide. An Arabidopsis mutant deficient in PPH (pph-1) is unable to degrade chlorophyll during senescence and therefore exhibits a stay-green phenotype. Furthermore, pph-1 accumulates phein during senescence. Therefore, PPH is an important component of the chlorophyll breakdown machinery of senescent leaves, and we propose that the sequence of early chlorophyll catabolic reactions be revised. Removal of Mg most likely precedes dephytylation, resulting in the following order of early breakdown intermediates: chlorophyll --> pheophytin --> Pheophorbide. Chlorophyllide, the last precursor of chlorophyll biosynthesis, is most likely not an intermediate of breakdown. Thus, chlorophyll anabolic and catabolic reactions are metabolically separated.
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stay green protein defective in mendel s green cotyledon mutant acts independent and upstream of Pheophorbide a oxygenase in the chlorophyll catabolic pathway
Plant Molecular Biology, 2008Co-Authors: Sylvain Aubry, Stefan Hortensteiner, Jan ManiAbstract:Type C stay-green mutants are defined as being defective in the pathway of chlorophyll breakdown, which involves Pheophorbide a oxygenase (PAO), required for loss of green color. By analyzing senescence parameters, such as protein degradation, expression of senescence-associated genes and loss of photosynthetic capacity, we demonstrate that JI2775, the green cotyledon (i) pea line used by Gregor Mendel to establish the law of genetics, is a true type C stay-green mutant. STAY-GREEN (SGR) had earlier been shown to map to the I locus. The defect in JI2775 is due to both reduced expression of SGR and loss of SGR protein function. Regulation of PAO through SGR had been proposed. By determining PAO protein abundance and activity, we show that PAO is unaffected in JI2775. Furthermore we show that Pheophorbide a accumulation in the mutant is independent of PAO. When silencing SGR expression in Arabidopsis pao1 mutant, both Pheophorbide a accumulation and cell death phenotype, typical features of pao1, are lost. These results confirm that SGR function within the chlorophyll catabolic pathway is independent and upstream of PAO.
Kenichiro Takamiya - One of the best experts on this subject based on the ideXlab platform.
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enzymatic conversion of Pheophorbide a to the precursor of pyroPheophorbide a in leaves of chenopodium album
Plant and Cell Physiology, 1996Co-Authors: Yuzo Shioi, Kenji Watanabe, Kenichiro TakamiyaAbstract:Soluble proteins extracted from leaves of Chenopodium album catalyzed the conversion of Pheophorbide a to a precursor of pyropheophorb ide a, putatively identified as C-132-carboxyl-pyroPheophorbide a. The precursor was then decarboxylated non-enzymatically to yield pyroPheophorbide a. Soluble proteins and Pheophorbide a, as the substrate, were required for the formation of the precursor, and boiled proteins were enzymatically inactive. The maximum rate of conversion of Pheophorbide a to the precursor occurred at pH 7.5. The Km for Pheophorbide a was 12.5 fiM at pH 7.0. Both Pheophorbide b and bacterioPheophorbide a could serve as substrates, but protoPheophorbide a could not. Formation of methanol was detected during the enzymatic reaction, an indication that the enzyme is an esterase. Among seven alcohol analogs tested, only methanol inhibited the enzymatic activity uncompetitively, with a K, of 71.6 mM. Mass-spectrometric (MS) analysis of the precursor yield a peak at m/z 579 that indicated the release of a methyl group from Pheophorbide a. It appears therefore that the enzyme catalyzes the demethylation of the carbomethoxy group at C-13 2 of Pheophorbide a by hydrolysis to yield methanol and the precursor, C-132carboxyl-pyroPheophorbide a, which is converted to pyroPheophorbide a by spontaneous decarboxylation. We have tentatively designated the enzyme "pheophorbidase". The presence of the enzyme was dependent on plant species and it was expressed constitutively.
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conversion of chlorophyllide to Pheophorbide by mg dechelating substance in extracts of chenopodium album
Plant Physiology and Biochemistry, 1996Co-Authors: Yuzo Shioi, N Tomita, T Tsuchiya, Kenichiro TakamiyaAbstract:Pheophorbide formation in chlorophyll metabolism was studied using extracts of Chenopodium album. A new substance catalyzing the conversion of chlorophyllide a to Pheophorbide a was found in the filtrate through Molcut II (Mr 5,000) of the extracts of C. album. The filtrate required chlorophyllide a as the sole substrate for Pheophorbide a formation, and the boiled filtrate had complete activity, indicating that this Mg-dechelating substance is heat stable. Optimum conversion of chlorophyllide a to Pheophorbide a was observed at pH 7 to 6.5 which is different from chemical formation of Pheophorbide a by acid. In addition to chlorophyllide a, this substance used chlorophyllide b, bacteriochlorophyllide a as the substrate, but not chlorophylls a and b, monovinyl-protochlorophyllide a and Mg-protoporphyrin IX dimethyl ester. The activity was stimulated by the addition of chelators such as EDTA and o-phenanthroline. The maximal activity was obtained at a concentration of 2 mM for EDTA. The activity was inhibited by the addition of Mg 2+ ion ; about 50% inhibition was observed at 10 mM MgCl 2 . These findings suggest that the substance catalyzing the conversion of chlorophyllide to Pheophorbide, tentatively called Mg-dechelating substance, is involved in the breakdown of chlorophylls.
V Navaratnam - One of the best experts on this subject based on the ideXlab platform.
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chemical constituents and in vitro anticancer activity of typhonium flagelliforme araceae
Journal of Ethnopharmacology, 2010Co-Authors: Choonsheen Lai, Rosemal H M H Mas, N K Nair, Sharif Mahsufi Mansor, V NavaratnamAbstract:Aim of the study: Typhonium flagelliforme is an indigenous plant of Malaysia and is used by the local communities to treat cancer. This study aims to identify the chemical constituents of Typhonium flagelliforme particularly those which have antiproliferative properties towards human cancer cell lines. Materials and methods: Purification of the chemical constituents by various chromatographic procedures was guided by the antiproliferative activity. Identification of the chemical constituents was carried out by various spectroscopic techniques including high resolution MS and NMR. The antiproliferative activity was assayed using MTT on NCI-H23 (lung cancer) and HS578T (breast cancer) cell lines. Microscopic observation and DeadEnd TM colourimetric TUNEL assay was used to identify the apoptotic mode of cell death. Results and conclusion: Four Pheophorbide related compounds, namely Pheophorbide-a, Pheophorbide-a� , pyroPheophorbide-a and methyl pyroPheophorbide-a were identified in the most active fraction, D/F19. These constituents exhibited antiproliferative activity against cancer cells and the activity increased following photoactivation. However, the greater antiproliferative activity exhibited by D/F19 itself compared to the Pheophorbides and its other subfractions suggests some form of synergistic action between the constituents. The inhibitory effect of D/F19 and the Pheophorbides was apoptotic in the absence of light. Other chemical constituents that have been identified in this study include hexadecanoic acid, oleic acid, linoleic acid, linolenic acid, campesterol, stigmasterol and -sitosterol. Most of the chemical constituents identified in this plant have not been reported previously. © 2009 Elsevier Ireland Ltd. All rights reserved.
Ayumi Tanaka - One of the best experts on this subject based on the ideXlab platform.
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conversion of chlorophyll b to chlorophyll a precedes magnesium dechelation for protection against necrosis in arabidopsis
Plant Journal, 2012Co-Authors: Yousuke Shimoda, Ayumi TanakaAbstract:Summary Chlorophyll is a deleterious molecule that generates reactive oxygen species and must be converted to non-toxic molecules during plant senescence. The degradation pathway of chlorophyll a has been determined; however, that of chlorophyll b is poorly understood, and multiple pathways of chlorophyll b degradation have been proposed. In this study, we found that chlorophyll b is degraded by a single pathway, and elucidated the importance of this pathway in avoiding cell death. In order to determine the chlorophyll degradation pathway, we first examined the substrate specificity of 7-hydroxymethyl chlorophyll a reductase. 7-hydroxymethyl chlorophyll a reductase reduces 7-hydroxymethyl chlorophyll a but not 7-hydroxymethyl pheophytin a or 7-hydroxymethyl Pheophorbide a. These results indicate that the first step of chlorophyll b degradation is its conversion to 7-hydroxymethyl chlorophyll a by chlorophyll b reductase, although chlorophyll b reductase has broad substrate specificity. In vitro experiments showed that chlorophyll b reductase converted all of the chlorophyll b in the light-harvesting chlorophyll a/b protein complex to 7-hydroxymethyl chlorophyll a, but did not completely convert chlorophyll b in the core antenna complexes. When plants whose core antennae contained chlorophyll b were incubated in the dark, chlorophyll b was not properly degraded, and the accumulation of 7-hydroxymethyl Pheophorbide a and Pheophorbide b resulted in cell death. This result indicates that chlorophyll b is not properly degraded when it exists in core antenna complexes. Based on these results, we discuss the importance of the proper degradation of chlorophyll b.
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light independent cell death induced by accumulation of Pheophorbide a in arabidopsis thaliana
Plant and Cell Physiology, 2009Co-Authors: Masumi Hirashima, Ryouichi Tanaka, Ayumi TanakaAbstract:Tetrapyrroles are well-known photosensitizers. In plants, various intermediate molecules of tetrapyrrole metabolism have been reported to induce cell death in a light-dependent manner. In contrast to these reports, we found that Pheophorbide a, a key intermediate of chlorophyll catabolism, causes cell death in complete darkness in a transgenic Arabidopsis plant, As-ACD1. In this plant, expression of mRNA for Pheophorbide a oxygenase was suppressed by expression of Acd1 antisense RNA; thus, As-ACD1 accumulated an excessive amount of Pheophorbide a when chlorophyll breakdown occurred. We observed that when senescence was induced by a continuous dark period, leaves of As-ACD1 plants became dehydrated. By measuring electrolyte leakage, we estimated that >50% of the leaf cells underwent cell death within a 5 d period of darkness. Light and electron microscopic observations indicated that the cellular structure had collapsed in a large population of cells. Partially covering a leaf with aluminum foil resulted in light-independent cell death in the covered region and induced bleaching in the uncovered regions. These results indicate that accumulation of Pheophorbide a induces cell death under both darkness and illumination, but the mechanisms of cell death under these conditions may differ. We discuss the possible mechanism of light-independent cell death and the involvement of Pheophorbide a in the signaling pathway for programmed cell death.
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the arabidopsis accelerated cell death gene acd1 is involved in oxygenation of Pheophorbide a inhibition of the Pheophorbide a oxygenase activity does not lead to the stay green phenotype in arabidopsis
Plant and Cell Physiology, 2003Co-Authors: Ryouichi Tanaka, Masumi Hirashima, Soichirou Satoh, Ayumi TanakaAbstract:Oxygenation of Pheophorbide a is a key step in chlorophyll breakdown. Several biochemical studies have implicated that this step was catalyzed by an iron-containing and ferredoxin-dependent monooxygenase, Pheophorbide a oxygenase (PaO). It has been proposed that inhibition of its activity arrests the chlorophyll breakdown and leads to the "stay-green" phenotype. We searched the Arabidopsis genome for a possible PaO-encoding gene and hypothesized that it has homology to known iron-containing Rieske-type monooxygenase sequences. We identified three such open reading frames, Tic55, ACD1 and ACD1-like. We produced transgenic Arabidopsis plants which expressed antisense RNA as a method to inhibit the expression of these genes. The appearance of these antisense plants were indistinguishable from that of the wild type under illumination. However, after they were kept under darkness for 5 d and again illuminated, the leaves of the antisense ACD1 plants (AsACD1) were bleached. Leaves of AsACD1 accumulated 387 nmol (g FW)(-1) Pheophorbide a which corresponded to 60% of chlorophyll a degraded. The rate of decrease in chlorophyll a was not influenced in senesced AsACD1 leaves. These results demonstrated that ACD1 is involved in PaO activity, and its inhibition led to photooxidative destruction of the cell instead of the "stay-green" phenotype.