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| 2. |
- Ankele, Elisabeth, et al.
(författare)
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In vivo visualization of Mg-ProtoporphyrinIX, a coordinator of photosynthetic gene expression in the nucleus and the chloroplast
- 2007
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Ingår i: Plant Cell. - Rockville Pike, Bethesda MD, USA : National Center for Biotechnology Information, U.S. National Library of Medicine. - 1040-4651 .- 1532-298X. ; 19:6, s. 1964-1979
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Tidskriftsartikel (refereegranskat)abstract
- The photosynthetic apparatus is composed of proteins encoded by genes from both the nucleus and the chloroplast. To ensure that the photosynthetic complexes are assembled stoichiometrically and to enable their rapid reorganization in response to a changing environment, the plastids emit signals that regulate nuclear gene expression to match the status of the plastids. One of the plastid signals, the chlorophyll intermediate Mg-ProtoporphyrinIX (Mg-ProtoIX) accumulates under stress conditions and acts as a negative regulator of photosynthetic gene expression. By taking advantage of the photoreactive property of tetrapyrroles, Mg-ProtoIX could be visualized in the cells using confocal laser scanning spectroscopy. Our results demonstrate that Mg-ProtoIX accumulated both in the chloroplast and in the cytosol during stress conditions. Thus, the signaling metabolite is exported from the chloroplast, transmitting the plastid signal to the cytosol. Our results from the Mg-ProtoIX over- and underaccumulating mutants copper response defect and genome uncoupled5, respectively, demonstrate that the expression of both nuclear- and plastid-encoded photosynthesis genes is regulated by the accumulation of Mg-ProtoIX. Thus, stress-induced accumulation of the signaling metabolite Mg-ProtoIX coordinates nuclear and plastidic photosynthetic gene expression.
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| 3. |
- Blaschek, Leonard, et al.
(författare)
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Cellular and Genetic Regulation of Coniferaldehyde Incorporation in Lignin of Herbaceous and Woody Plants by Quantitative Wiesner Staining
- 2020
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Ingår i: Frontiers in Plant Science. - : Frontiers Media S.A.. - 1664-462X. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Lignin accumulates in the cell walls of specialized cell types to enable plants to stand upright and conduct water and minerals, withstand abiotic stresses, and defend themselves against pathogens. These functions depend on specific lignin concentrations and subunit composition in different cell types and cell wall layers. However, the mechanisms controlling the accumulation of specific lignin subunits, such as coniferaldehyde, during the development of these different cell types are still poorly understood. We herein validated the Wiesner test (phloroglucinol/HCl) for the restrictive quantitative in situ analysis of coniferaldehyde incorporation in lignin. Using this optimized tool, we investigated the genetic control of coniferaldehyde incorporation in the different cell types of genetically-engineered herbaceous and woody plants with modified lignin content and/or composition. Our results demonstrate that the incorporation of coniferaldehyde in lignified cells is controlled by (a) autonomous biosynthetic routes for each cell type, combined with (b) distinct cell-to-cell cooperation between specific cell types, and (c) cell wall layer-specific accumulation capacity. This process tightly regulates coniferaldehyde residue accumulation in specific cell types to adapt their property and/or function to developmental and/or environmental changes.
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| 4. |
- Blaschek, Leonard, 1992-
(författare)
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Cellular Control and Physiological Importance of Vascular Lignification
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignin is indispensable for vascular plants. It allows their cells to coalesce into gravity-defying giants, hardens them to withstand pressures and predators, and waterproofs them to allow the flow of water only where it is advantageous. Lignin fulfils these different functions as a structural component of specialised cell walls in a wide range of different tissues and cell types. Between them, lignin shows great heterogeneity in its concentration and composition. The biosynthesis of lignin proceeds via monomer biosynthesis in the cell, export of the monomers into the apoplast and oxidative polymerisation by laccases (LACs) and class III peroxidases (PRXs) in the cell wall. In this thesis, I investigated how these processes are regulated to allow distinct lignification programs in different cell types and even adjacent cell wall layers (I–III) and what physiological advantages these differences in lignin amount and composition confer to the plant (IV). In paper I and II, we optimised and validated the histochemical Wiesner test and Raman microspectroscopy for the in situ quantitative analysis of lignin. We then used those techniques to map the cell autonomous and cell–cell cooperative genetic programs that regulate lignin monomer biosynthesis in the vasculature of Arabidopsis thaliana and Populus. Because lignin monomers are mobile in the cell wall prior to polymerisation, the sophisticated, cell type-specific genetic regulation of lignin monomer biosynthesis alone cannot explain the lignin differences observed between adjacent cell wall layers. In paper III, we therefore characterised five LACs paralogs involved in lignification, showing that they fine-tuned lignification at the nanoscale through distinct patterns of activity and substrate specificity. But what is the advantage of such a complex, layered control of lignification? In paper IV we began to answer this question by showing that different cell types – and even the same cell type in different developmental contexts – relied on distinct lignin amounts and compositions to withstand the unique stresses they were exposed to. Altogether, the work presented herein highlights how finely lignification is controlled the on cellular and sub-cellular scale, and how this regulation allows plants to fully exploit the versatile functions of lignin.
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| 5. |
- Blaschek, Leonard, et al.
(författare)
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Different combinations of laccase paralogs nonredundantly control the amount and composition of lignin in specific cell types and cell wall layers in Arabidopsis
- 2023
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Ingår i: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 35:2, s. 889-909
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Tidskriftsartikel (refereegranskat)abstract
- Vascular plants reinforce the cell walls of the different xylem cell types with lignin phenolic polymers. Distinct lignin chemistries differ between each cell wall layer and each cell type to support their specific functions. Yet the mechanisms controlling the tight spatial localization of specific lignin chemistries remain unclear. Current hypotheses focus on control by monomer biosynthesis and/or export, while cell wall polymerization is viewed as random and nonlimiting. Here, we show that combinations of multiple individual laccases (LACs) are nonredundantly and specifically required to set the lignin chemistry in different cell types and their distinct cell wall layers. We dissected the roles of Arabidopsis thaliana LAC4, 5, 10, 12, and 17 by generating quadruple and quintuple loss-of-function mutants. Loss of these LACs in different combinations led to specific changes in lignin chemistry affecting both residue ring structures and/or aliphatic tails in specific cell types and cell wall layers. Moreover, we showed that LAC-mediated lignification has distinct functions in specific cell types, waterproofing fibers, and strengthening vessels. Altogether, we propose that the spatial control of lignin chemistry depends on different combinations of LACs with nonredundant activities immobilized in specific cell types and cell wall layers.
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| 6. |
- Blaschek, Leonard, et al.
(författare)
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Functional Complexity on a Cellular Scale : Why In Situ Analyses Are Indispensable for Our Understanding of Lignified Tissues
- 2024
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Ingår i: Journal of Agricultural and Food Chemistry. - : American Chemical Society (ACS). - 0021-8561 .- 1520-5118. ; 72:24, s. 13552-13560
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Forskningsöversikt (refereegranskat)abstract
- Lignins are a key adaptation that enables vascular plants to thrive in terrestrial habitats. Lignin is heterogeneous, containing upward of 30 different monomers, and its function is multifarious: It provides structural support, predetermined breaking points, ultraviolet protection, diffusion barriers, pathogen resistance, and drought resilience. Recent studies, carefully characterizing lignin in situ, have started to identify specific lignin compositions and ultrastructures with distinct cellular functions, but our understanding remains fractional. We summarize recent works and highlight where further in situ lignin analysis could provide valuable insights into plant growth and adaptation. We also summarize strengths and weaknesses of lignin in situ analysis methods.
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| 7. |
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| 8. |
- Courtois-Moreau, Charleen L, et al.
(författare)
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A unique program for cell death in xylem fibers of Populus stem
- 2009
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Ingår i: The Plant Journal. - 0960-7412 .- 1365-313X. ; 58:2, s. 260-274
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Tidskriftsartikel (refereegranskat)abstract
- Maturation of the xylem elements involves extensive deposition of secondary cell-wall material and autolytic processes resulting in cell death. We describe here a unique type of cell-death program in xylem fibers of hybrid aspen (Populus tremula x P. tremuloides) stems, including gradual degradative processes in both the nucleus and cytoplasm concurrently with the phase of active cell-wall deposition. Nuclear DNA integrity, as determined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) and Comet (single-cell gel electrophoresis) assays, was compromised early during fiber maturation. In addition, degradation of the cytoplasmic contents, as detected by electron microscopy of samples fixed by high-pressure freezing/freeze substitution (HPF-FS), was gradual and resulted in complete loss of the cytoplasmic contents well before the loss of vacuolar integrity, which is considered to be the moment of death. This type of cell death differs significantly from that seen in xylem vessels. The loss of vacuolar integrity, which is thought to initiate cell degradative processes in the xylem vessels, is one of the last processes to occur before the final autolysis of the remaining cell contents in xylem fibers. High-resolution microarray analysis in the vascular tissues of Populus stem, combined with in silico analysis of publicly available data repositories, suggests the involvement of several previously uncharacterized transcription factors, ethylene, sphingolipids and light signaling as well as autophagy in the control of fiber cell death.
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| 9. |
- Decou, Raphaël, et al.
(författare)
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Analysis of lignin composition and distribution using fluorescence laser confocal microspectroscopy
- 2017. - 1
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Ingår i: Xylem. - New York : Humana Press. - 9781493967209 - 9781493967223 ; , s. 233-247
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Bokkapitel (refereegranskat)abstract
- Lignin is a polyphenolic polymer specifically accumulating in the cell walls of xylem cells in higher vascular plants. Far from being homogeneous, the lignification of xylem cell walls varies in deposition site, quantity, composition and macromolecular conformation depending on the cell wall compartment, cell type, cell developmental stage and plant species. Here, we describe how confocal microspectroscopy methods using lignin autofluorescence can be used to evaluate the relative lignin amounts, its spatial distribution and composition at the cellular and sub-cellular levels in both isolated cells and histological cross-sections of plant tissues.
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| 10. |
- Escamez, Sacha, 1987-, et al.
(författare)
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METACASPASE9 modulates autophagy to confine cell death tothe target cells during Arabidopsis vascular xylem differentiation
- 2016
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Ingår i: Biology Open. - : The Company of Biologists ltd. - 2046-6390. ; 5:2, s. 122-129
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Tidskriftsartikel (refereegranskat)abstract
- We uncovered that the level of autophagy in plant cells undergoingprogrammed cell death determines the fate of the surrounding cells.Our approach consisted of using Arabidopsis thaliana cell culturescapable of differentiating into two different cell types: vasculartracheary elements (TEs) that undergo programmed cell death(PCD) and protoplast autolysis, and parenchymatic non-TEs thatremain alive. The TE cell type displayed higher levels of autophagywhen expression of the TE-specific METACASPASE9 (MC9) wasreduced using RNAi (MC9-RNAi). Misregulation of autophagy in theMC9-RNAi TEs coincided with ectopic death of the non-TEs, implyingthe existence of an autophagy-dependent intercellular signallingfrom within the TEs towards the non-TEs. Viability of the non-TEswas restored when AUTOPHAGY2 (ATG2) was downregulatedspecifically in MC9-RNAi TEs, demonstrating the importance ofautophagy in the spatial confinement of cell death. Our resultssuggest that other eukaryotic cells undergoing PCD might also needto tightly regulate their level of autophagy to avoid detrimentalconsequences for the surrounding cells.
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