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1.	Abedi, Tayebeh, et al. (författare) The Spatio-Temporal Distribution of Cell Wall-Associated Glycoproteins During Wood Formation in Populus 2020 Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 11 Tidskriftsartikel (refereegranskat)abstract Plant cell wall associated hydroxyproline-rich glycoproteins (HRGPs) are involved in several aspects of plant growth and development, including wood formation in trees. HRGPs such as arabinogalactan-proteins (AGPs), extensins (EXTs), and proline rich proteins (PRPs) are important for the development and architecture of plant cell walls. Analysis of publicly available gene expression data revealed that many HRGP encoding genes show tight spatio-temporal expression patterns in the developing wood of Populus that are indicative of specific functions during wood formation. Similar results were obtained for the expression of glycosyl transferases putatively involved in HRGP glycosylation. In situ immunolabelling of transverse wood sections using AGP and EXT antibodies revealed the cell type specificity of different epitopes. In mature wood AGP epitopes were located in xylem ray cell walls, whereas EXT epitopes were specifically observed between neighboring xylem vessels, and on the ray cell side of the vessel walls, likely in association with pits. Molecular mass and glycan analysis of AGPs and EXTs in phloem/cambium, developing xylem, and mature xylem revealed clear differences in glycan structures and size between the tissues. Separation of AGPs by agarose gel electrophoresis and staining with beta-D-glucosyl Yariv confirmed the presence of different AGP populations in phloem/cambium and xylem. These results reveal the diverse changes in HRGP-related processes that occur during wood formation at the gene expression and HRGP glycan biosynthesis levels, and relate HRGPs and glycosylation processes to the developmental processes of wood formation.
2.	Abreu, Ilka, et al. (författare) A metabolite roadmap of the wood-forming tissue in Populus tremula 2020 Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 228:5, s. 1559-1572 Tidskriftsartikel (refereegranskat)abstract Wood, or secondary xylem, is the product of xylogenesis, a developmental process that begins with the proliferation of cambial derivatives and ends with mature xylem fibers and vessels with lignified secondary cell walls. Fully mature xylem has undergone a series of cellular processes, including cell division, cell expansion, secondary wall formation, lignification and programmed cell death. A complex network of interactions between transcriptional regulators and signal transduction pathways controls wood formation. However, the role of metabolites during this developmental process has not been comprehensively characterized. To evaluate the role of metabolites during wood formation, we performed a high spatial resolution metabolomics study of the wood-forming zone of Populus tremula, including laser dissected aspen ray and fiber cells. We show that metabolites show specific patterns within the wood-forming zone, following the differentiation process from cell division to cell death. The data from profiled laser dissected aspen ray and fiber cells suggests that these two cell types host distinctly different metabolic processes. Furthermore, by integrating previously published transcriptomic and proteomic profiles generated from the same trees, we provide an integrative picture of molecular processes, for example, deamination of phenylalanine during lignification is of critical importance for nitrogen metabolism during wood formation.
3.	Baison, John, et al. (författare) Genome-Wide Association Study (GWAS) identified novel candidate loci affecting wood formation in Norway spruce 2019 Ingår i: The Plant Journal. - : Wiley. - 0960-7412 .- 1365-313X. ; 100:1, s. 83-100 Tidskriftsartikel (refereegranskat)abstract Norway spruce is a boreal forest tree species of significant ecological and economic importance. Hence there is a strong imperative to dissect the genetics underlying important wood quality traits in the species. We performed a functional Genome-Wide Association Study (GWAS) of 17 wood traits in Norway spruce using 178101 single-nucleotide polymorphisms (SNPs) generated from exome genotyping of 517 mother trees. The wood traits were defined using functional modelling of wood properties across annual growth rings.We applied a LASSO based association mapping method using a functional multi-locus mapping approach that utilizes latent traits, with a stability selection probability method as the hypothesis testing approach to determine significant Quantitative Trait Loci (QTLs). The analysis provided 52 significant SNPs from 39 candidate genes, including genes previously implicated in wood formation and tree growth in spruce and other species. Our study represents a multi-locus GWAS for complex wood traits in Norway spruce. The results advance our understanding of the genetics influencing wood traits and identifies candidate genes for future functional studies.
4.	Baison, John, et al. (författare) Genome-wide association study identified novel candidate loci affecting wood formation in Norway spruce 2019 Ingår i: The Plant Journal. - : John Wiley & Sons. - 0960-7412 .- 1365-313X. ; 100:1, s. 83-100 Tidskriftsartikel (refereegranskat)abstract Norway spruce is a boreal forest tree species of significant ecological and economic importance. Hence there is a strong imperative to dissect the genetics underlying important wood quality traits in the species. We performed a functional genome-wide association study (GWAS) of 17 wood traits in Norway spruce using 178 101 single nucleotide polymorphisms (SNPs) generated from exome genotyping of 517 mother trees. The wood traits were defined using functional modelling of wood properties across annual growth rings. We applied a Least Absolute Shrinkage and Selection Operator (LASSO-based) association mapping method using a functional multilocus mapping approach that utilizes latent traits, with a stability selection probability method as the hypothesis testing approach to determine a significant quantitative trait locus. The analysis provided 52 significant SNPs from 39 candidate genes, including genes previously implicated in wood formation and tree growth in spruce and other species. Our study represents a multilocus GWAS for complex wood traits in Norway spruce. The results advance our understanding of the genetics influencing wood traits and identifies candidate genes for future functional studies.
5.	Baş, Yağmur, et al. (författare) Preparation and Characterization of Softwood and Hardwood Nanofibril Hydrogels: Toward Wound Dressing Applications 2023 Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 24:12, s. 5605-5619 Tidskriftsartikel (refereegranskat)abstract Hydrogels of cellulose nanofibrils (CNFs) are promising wound dressing candidates due to their biocompatibility, high water absorption, and transparency. Herein, two different commercially available wood species, softwood and hardwood, were subjected to TEMPO-mediated oxidation to proceed with delignification and oxidation in a one-pot process, and thereafter, nanofibrils were isolated using a high-pressure microfluidizer. Furthermore, transparent nanofibril hydrogel networks were prepared by vacuum filtration. Nanofibril properties and network performance correlated with oxidation were investigated and compared with commercially available TEMPO-oxidized pulp nanofibrils and their networks. Softwood nanofibril hydrogel networks exhibited the best mechanical properties, and in vitro toxicological risk assessment showed no detrimental effect for any of the studied hydrogels on human fibroblast or keratinocyte cells. This study demonstrates a straightforward processing route for direct oxidation of different wood species to obtain nanofibril hydrogels for potential use as wound dressings, with softwood having the most potential.
6.	Bünder, Anne, et al. (författare) CELLULOSE SYNTHASE INTERACTING 1 is required for wood mechanics and leaf morphology in aspen 2020 Ingår i: The Plant Journal. - : John Wiley & Sons. - 0960-7412 .- 1365-313X. ; 103:5, s. 1858-1868 Tidskriftsartikel (refereegranskat)abstract Cellulose microfibrils synthesized by CELLULOSE SYNTHASE COMPLEXES (CSCs) are the main load‐bearing polymers in wood. CELLULOSE SYNTHASE INTERACTING1 (CSI1) connects CSCs with cortical microtubules, which align with cellulose microfibrils. Mechanical properties of wood are dependent on cellulose microfibril alignment and structure in the cell walls, but the molecular mechanism(s) defining these features is unknown. Herein, we investigated the role of CSI1 in hybrid aspen (Populus tremula × Populus tremuloides ) by characterizing transgenic lines with significantly reduced CSI1 transcript abundance. Reduction in leaves (50–80%) caused leaf twisting and misshaped pavement cells, while reduction (70–90%) in developing xylem led to impaired mechanical wood properties evident as a decrease in the elastic modulus and rupture. X‐ray diffraction measurements indicate that microfibril angle was not impacted by the altered CSI1 abundance in developing wood fibres. Instead, the augmented wood phenotype of the transgenic trees was associated with a reduced cellulose degree of polymerization. These findings establish a function for CSI1 in wood mechanics and in defining leaf cell shape. Furthermore, the results imply that the microfibril angle in wood is defined by CSI1 independent mechanism(s).
7.	Christoffer, Johnsson, et al. (författare) Framtidens skogsbruk : utveckling av nya träd och vedbaserade produkter 2016 Ingår i: Fakta. Skog. - 1400-7789. Annan publikation (populärvet., debatt m.m.)
8.	Diacci, Chiara, et al. (författare) Diurnal in vivo xylem sap glucose and sucrose monitoring using implantable organic electrochemical transistor sensors 2021 Ingår i: iScience. - : Cell Press. - 2589-0042. ; 24:1 Tidskriftsartikel (refereegranskat)abstract Bioelectronic devices that convert biochemical signals to electronic readout enable biosensing with high spatiotemporal resolution. These technologies have been primarily applied in biomedicine while in plants sensing is mainly based on invasive methods that require tissue sampling, hindering in-vivo detection and having poor spatiotemporal resolution. Here, we developed enzymatic biosensors based on organic electrochemical transistors (OECTs) for in-vivo and real-time monitoring of sugar fluctuations in the vascular tissue of trees. The glucose and sucrose OECT-biosensors were implanted into the vascular tissue of trees and were operated through a low-cost portable unit for 48hr. Our work consists a proof-of-concept study where implantable OECT-biosensors not only allow real-time monitoring of metabolites in plants but also reveal new insights into diurnal sugar homeostasis. We anticipate that this work will contribute to establishing bioelectronic technologies as powerful minimally invasive tools in plant science, agriculture and forestry.
9.	Dominguez, Pia Guadalupe, et al. (författare) Sucrose synthase determines carbon allocation in developing wood and alters carbon flow at the whole tree level in aspen 2021 Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 229:1, s. 186-198 Tidskriftsartikel (refereegranskat)abstract Despite the ecological and industrial importance of biomass accumulation in wood, the control of carbon (C) allocation to this tissue and to other tree tissues remain poorly understood. We studied sucrose synthase (SUS) to clarify its role in biomass formation and C metabolism at the whole tree level in hybrid aspen (Populus tremula x tremuloides). To this end, we analysed source leaves, phloem, developing wood, and roots ofSUSRNAitrees using a combination of metabolite profiling, 13CO2 pulse labelling experiments, and long-term field experiments. The glasshouse grownSUSRNAitrees exhibited a mild stem phenotype together with a reduction in wood total C. The 13CO2 pulse labelling experiments showed an alteration in the C flow in all the analysed tissues, indicating that SUS affects C metabolism at the whole tree level. This was confirmed when theSUSRNAitrees were grown in the field over a 5-yr period; their stem height, diameter and biomass were substantially reduced. These results establish that SUS influences C allocation to developing wood, and that it affects C metabolism at the whole tree level.
10.	Escamez, Sacha, 1987-, et al. (författare) Fluorescence Lifetime Imaging as an in Situ and Label-Free Readout for the Chemical Composition of Lignin 2021 Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society. - 2168-0485. ; 9:51 Tidskriftsartikel (refereegranskat)abstract Naturally fluorescent polymeric molecules such as collagen, resilin, cutin, suberin, or lignin can serve as renewable sources of bioproducts. Theoretical physics predicts that the fluorescence lifetime of these polymers is related to their chemical composition. We verified this prediction for lignin, a major structural element in plant cell walls that form woody biomass. Lignin is composed of different phenylpropanoid units, and its composition affects its properties, biological functions, and the utilization of wood biomass. We carried out fluorescence lifetime imaging microscopy (FLIM) measurements of wood cell wall lignin in a population of 90 hybrid aspen trees genetically engineered to display differences in cell wall chemistry and structure. We also measured the wood cell wall composition by classical analytical methods in these trees. Using statistical modeling and machine learning algorithms, we identified parameters of fluorescence lifetime that predict the content of S-type and G-type lignin units, the two main types of units in the lignin of angiosperm (flowering) plants. In a first step toward tailoring lignin biosynthesis toward improvement of woody biomass feedstocks, we show how FLIM can reveal the dynamics of lignin biosynthesis in two different biological contexts, including in vivo while lignin is being synthesized in the walls of living cells. © 2021 The Authors.
11.	Gerber, Lorenz, et al. (författare) Deficient sucrose synthase activity in developing wood does not specifically affect cellulose biosynthesis, but causes an overall decrease in cell wall polymers 2014 Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 203, s. 1220-1230 Tidskriftsartikel (refereegranskat)abstract The biosynthesis of wood in aspen (Populus) depends on the metabolism of sucrose, which is the main transported form of carbon from source tissues. The largest fraction of the wood biomass is cellulose, which is synthesized from UDP-glucose. Sucrose synthase (SUS) has been proposed previously to interact directly with cellulose synthase complexes and specifically supply UDP-glucose for cellulose biosynthesis.To investigate the role of SUS in wood biosynthesis, we characterized transgenic lines of hybrid aspen with strongly reduced SUS activity in developing wood.No dramatic growth phenotypes in glasshouse-grown trees were observed, but chemical fingerprinting with pyrolysis-GC/MS, together with micromechanical analysis, showed notable changes in chemistry and ultrastructure of the wood in the transgenic lines. Wet chemical analysis showed that the dry weight percentage composition of wood polymers was not changed significantly. However, a decrease in wood density was observed and, consequently, the content of lignin, hemicellulose and cellulose was decreased per wood volume. The decrease in density was explained by a looser structure of fibre cell walls as shown by increased wall shrinkage on drying.The results show that SUS is not essential for cellulose biosynthesis, but plays a role in defining the total carbon incorporation to wood cell walls.
12.	Jonasson, Simon, et al. (författare) Characteristics of Cellulose Nanofibrils from Transgenic Trees with Reduced Expression of Cellulose Synthase Interacting 1 2022 Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 12:19 Tidskriftsartikel (refereegranskat)abstract Cellulose nanofibrils can be derived from the native load-bearing cellulose microfibrils in wood. These microfibrils are synthesized by a cellulose synthase enzyme complex that resides in the plasma membrane of developing wood cells. It was previously shown that transgenic hybrid aspen trees with reduced expression of CSI1 have different wood mechanics and cellulose microfibril properties. We hypothesized that these changes in the native cellulose may affect the quality of the corresponding nanofibrils. To test this hypothesis, wood from wild-type and transgenic trees with reduced expression of CSI1 was subjected to oxidative nanofibril isolation. The transgenic wood-extracted nanofibrils exhibited a significantly lower suspension viscosity and estimated surface area than the wild-type nanofibrils. Furthermore, the nanofibril networks manufactured from the transgenics exhibited high stiffness, as well as reduced water uptake, tensile strength, strain-to-break, and degree of polymerization. Presumably, the difference in wood properties caused by the decreased expression of CSI1 resulted in nanofibrils with distinctive qualities. The observed changes in the physicochemical properties suggest that the differences were caused by changes in the apparent nanofibril aspect ratio and surface accessibility. This study demonstrates the possibility of influencing wood-derived nanofibril quality through the genetic engineering of trees.
13.	Jonasson, Simon, et al. (författare) Comparison of tension wood and normal wood for oxidative nanofibrillation and network characteristics 2021 Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 28:2, s. 1085-1104 Tidskriftsartikel (refereegranskat)abstract Cellulose nanofibrils (CNFs) are top-down nanomaterials obtainable from abundant lignocelluloses. Despite recent advances in processing technologies, the effects of variations in the lignocellulose structure and composition on CNF isolation and properties are poorly understood. In this study, we compared the isolation of CNFs from tension wood (TW) and normal wood (NW) from Populus tremula (aspen). The TW has a higher cellulose content, native cellulose fibrils with a larger crystalline diameter, and less lignin than the NW, making it an interesting material for CNF isolation. The wood powders were oxidized directly by 2,2,6,6-tetramethylpiperidin-1-oxyl, and the morphology and mechanical behaviors of the nanofibril suspensions and networks were characterized. The TW was more difficult to fibrillate by both chemical and mechanical means. Larger nanofibrils (5–10 nm) composed of 1.2 nm structures were present in the TW CNFs, whereas the NW samples contained more of thin (1.6 nm) structures, which also comprised 77% of the solid yield compared to the 33% for TW. This difference was reflected in the TW CNF networks as decreased transmittance (15% vs. 50%), higher degree of crystallinity (85.9% vs. 78.0%), doubled toughness (11 MJ/m3) and higher elongation at break (12%) compared to NW. The difference was ascribed to greater preservation of the hierarchical, more crystalline microfibril structure, combined with a more cellulose-rich network (84% vs. 70%). This knowledge of the processing, structure, and properties of CNFs can facilitate the breeding and design of wood feedstocks to meet the increasing demand for nanoscale renewable materials.
14.	Jonasson, Simon, et al. (författare) Isolation and characterization of cellulose nanofibers from aspen wood using derivatizing and non-derivatizing pretreatments 2020 Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 27:1, s. 185-203 Tidskriftsartikel (refereegranskat)abstract The link between wood and corresponding cellulose nanofiber (CNF) behavior is complex owing the multiple chemical pretreatments required for successful preparation. In this study we apply a few pretreatments on aspen wood and compare the final CNF behavior in order to rationalize quantitative studies of CNFs derived from aspen wood with variable properties. This is relevant for efforts to improve the properties of woody biomass through tree breeding. Three different types of pretreatments were applied prior to disintegration (microfluidizer) after a mild pulping step; derivatizing TEMPO-oxidation, carboxymethylation and non-derivatizing soaking in deep-eutectic solvents. TEMPO-oxidation was also performed directly on the plain wood powder without pulping. Obtained CNFs (44–55% yield) had hemicellulose content between 8 and 26 wt% and were characterized primarily by fine (height ≈ 2 nm) and coarser (2 nm < height < 100 nm) grade CNFs from the derivatizing and non-derivatizing treatments, respectively. Nanopapers from non-derivatized CNFs had higher thermal stability (280 °C) compared to carboxymethylated (260 °C) and TEMPO-oxidized (220 °C). Stiffness of nanopapers made from non-derivatized treatments was higher whilst having less tensile strength and elongation-at-break than those made from derivatized CNFs. The direct TEMPO-oxidized CNFs and nanopapers were furthermore morphologically and mechanically indistinguishable from those that also underwent a pulping step. The results show that utilizing both derivatizing and non-derivatizing pretreatments can facilitate studies of the relationship between wood properties and final CNF behavior. This can be valuable when studying engineered trees for the purpose of decreasing resource consumption when isolation cellulose nanomaterials.
15.	Jonasson, Simon, et al. (författare) Mechanical-chemical nanofiber extractability of woodwith variable ultrastructure and composition throughone-pot oxidative pretreatments 2019 Ingår i: 6<sup>th</sup> EPNOE International Polysaccharide Conference. - : European Polysaccharide Network of Excellence (EPNOE). ; , s. 114-114 Konferensbidrag (refereegranskat)abstract Isolation of high value nanofibers from lignocellulosic feedstocks is a costly and resource intensive process. This stems from the complex structure of the raw material which contains hierarchical crystalline cellulose within hydrophobic lignin layers. This inherent structure makes inquiries regarding suitability of a certain lignocellulose for nanofibrillation difficult. Further nuances are present due to the common usage of both mechanical and chemical processing, often using pre-delignified wood as starting material.In this study we look at how the isolation of nanofibers is a↵ected by inherent wood properties by nanofibrillating wood from trees that has been physically stimulated to produce biomass with higher cellulose/lignin ratio and a different cell wall structure. Cryocrushed samples have been processed with i) mechanical, ii) chemical and iii) mechanical-chemical treatments, where (one-pot) direct TEMPO-catalyzed oxidation with different severity and high-pressure homogenization serve as controlled chemical and mechanical factors, respectively.The nanofibers have been characterized in suspension according to traditional procedures regarding degree of fibrillation, and then made into dense nanopapers for mechanical characterization. The material behavior is discussed in relation to the structure of the initial biomass and corresponding fibrillation efficiency. The results are presented in terms of both mechanical disintegration and chemical (carboxylation) derivatization.
16.	Jonasson, Simon, et al. (författare) The Effect of High Lignin Content on Oxidative Nanofibrillation of Wood Cell Wall 2021 Ingår i: Nanomaterials. - : MDPI. - 2079-4991. ; 11:5 Tidskriftsartikel (refereegranskat)abstract Wood from field-grown poplars with different genotypes and varying lignin content (17.4 wt % to 30.0 wt %) were subjected to one-pot 2,2,6,6-Tetramethylpiperidin-1-yl)oxyl catalyzed oxidation and high-pressure homogenization in order to investigate nanofibrillation following simultaneous delignification and cellulose oxidation. When comparing low and high lignin wood it was found that the high lignin wood was more easily fibrillated as indicated by a higher nanofibril yield (68% and 45%) and suspension viscosity (27 and 15 mPa·s). The nanofibrils were monodisperse with diameter ranging between 1.2 and 2.0 nm as measured using atomic force microscopy. Slightly less cellulose oxidation (0.44 and 0.68 mmol·g−1) together with a reduced process yield (36% and 44%) was also found which showed that the removal of a larger amount of lignin increased the efficiency of the homogenization step despite slightly reduced oxidation of the nanofibril surfaces. The surface area of oxidized high lignin wood was also higher than low lignin wood (114 m2·g−1 and 76 m2·g−1) which implicates porosity as a factor that can influence cellulose nanofibril isolation from wood in a beneficial manner.
17.	Mahboubi, Miramirhossein, et al. (författare) Aspen SUCROSE TRANSPORTER3 Allocates Carbon into Wood Fibers 2013 Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 163, s. 1729-1740 Tidskriftsartikel (refereegranskat)abstract Wood formation in trees requires carbon import from the photosynthetic tissues. In several tree species, including Populus species, the majority of this carbon is derived from sucrose (Suc) transported in the phloem. The mechanism of radial Suc transport from phloem to developing wood is not well understood. We investigated the role of active Suc transport during secondary cell wall formation in hybrid aspen (Populus tremula x Populus tremuloides). We show that RNA interference-mediated reduction of PttSUT3 (for Suc/H+ symporter) during secondary cell wall formation in developing wood caused thinner wood fiber walls accompanied by a reduction in cellulose and an increase in lignin. Suc content in the phloem and developing wood was not significantly changed. However, after (CO2)-C-13 assimilation, the SUT3RNAi lines contained more C-13 than the wild type in the Suc-containing extract of developing wood. Hence, Suc was transported into developing wood, but the Suc-derived carbon was not efficiently incorporated to wood fiber walls. A yellow fluorescent protein: PttSUT3 fusion localized to plasma membrane, suggesting that reduced Suc import into developing wood fibers was the cause of the observed cell wall phenotype. The results show the importance of active Suc transport for wood formation in a symplasmically phloem-loading tree species and identify PttSUT3 as a principal transporter for carbon delivery into secondary cell wall-forming wood fibers.
18.	Mahboubi, Miramirhossein, et al. (författare) C-13 Tracking after (CO2)-C-13 Supply Revealed Diurnal Patterns of Wood Formation in Aspen 2015 Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 168, s. 478-489 Tidskriftsartikel (refereegranskat)abstract Wood of trees is formed from carbon assimilated in the photosynthetic tissues. Determining the temporal dynamics of carbon assimilation, subsequent transport into developing wood, and incorporation to cell walls would further our understanding of wood formation in particular and tree growth in general. To investigate these questions, we designed a (CO2)-C-13 labeling system to study carbon transport and incorporation to developing wood of hybrid aspen (Populus tremula 3 tremuloides). Tracking of C-13 incorporation to wood over a time course using nuclear magnetic resonance spectroscopy revealed diurnal patterns in wood cell wall biosynthesis. The dark period had a differential effect on C-13 incorporation to lignin and cell wall carbohydrates. No C-13 was incorporated into aromatic amino acids of cell wall proteins in the dark, suggesting that cell wall protein biosynthesis ceased during the night. The results show previously unrecognized temporal patterns in wood cell wall biosynthesis, suggest diurnal cycle as a possible cue in the regulation of carbon incorporation to wood, and establish a unique C-13 labeling method for the analysis of wood formation and secondary growth in trees.
19.	Mahboubi, Miramirhossein, et al. (författare) Sucrose transport and carbon fluxes during wood formation 2018 Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 164, s. 67-81 Tidskriftsartikel (refereegranskat)abstract Wood biosynthesis defines the chemical and structural properties of wood. The metabolic pathways that produce the precursors of wood cell wall polymers have a central role in defining wood properties. To make rational design of wood properties feasible, we need not only to understand the cell wall biosynthetic machinery, but also how sucrose transport and metabolism in developing wood connect to cell wall biosynthesis and how they respond to genetic and environmental cues. Here, we review the current understanding of the sucrose transport and primary metabolism pathways leading to the precursors of cell wall biosynthesis in woody plant tissues. We present both old, persistent questions and new emerging themes with a focus on wood formation in trees and draw upon evidence from the xylem tissues of herbaceous plants when it is relevant.
20.	Nibbering, Petrus, et al. (författare) CAGEs are Golgi-localized GT31 enzymes involved in cellulose biosynthesis in Arabidopsis 2022 Ingår i: Plant Journal. - : Wiley. - 0960-7412 .- 1365-313X. ; 110, s. 1271-1285 Tidskriftsartikel (refereegranskat)abstract Cellulose is the main structural component in the plant cell walls. We show that two glycosyltransferase family 31 (GT31) enzymes of Arabidopsis thaliana, here named cellulose synthesis associated glycosyltransferases 1 and 2 (CAGE1 and 2), influence both primary and secondary cell wall cellulose biosynthesis. cage1cage2 mutants show primary cell wall defects manifesting as impaired growth and cell expansion in seedlings and etiolated hypocotyls, along with secondary cell wall defects, apparent as collapsed xylem vessels and reduced xylem wall thickness in the inflorescence stem. Single and double cage mutants also show increased sensitivity to the cellulose biosynthesis inhibitor isoxaben. The cage1cage2 phenotypes were associated with an approximately 30% reduction in cellulose content, an approximately 50% reduction in secondary cell wall CELLULOSE SYNTHASE (CESA) protein levels in stems and reduced cellulose biosynthesis rate in seedlings. CESA transcript levels were not significantly altered in cage1cage2 mutants, suggesting that the reduction in CESA levels was caused by a post-transcriptional mechanism. Both CAGE1 and 2 localize to the Golgi apparatus and are predicted to synthesize beta-1,3-galactans on arabinogalactan proteins. In line with this, the cage1cage2 mutants exhibit reduced levels of beta-Yariv binding to arabinogalactan protein linked beta-1,3-galactan. This leads us to hypothesize that defects in arabinogalactan biosynthesis underlie the cellulose deficiency of the mutants.
21.	Nibbering, Petrus, et al. (författare) Golgi-localized exo-beta 1,3-galactosidases involved in cell expansion and root growth in Arabidopsis 2020 Ingår i: Journal of Biological Chemistry. - 0021-9258 .- 1083-351X. ; 295, s. 10581-10592 Tidskriftsartikel (refereegranskat)abstract Plant arabinogalactan proteins (AGPs) are a diverse group of cell surface- and wall-associated glycoproteins. Functionally important AGP glycans are synthesized in the Golgi apparatus, but the relationships among their glycosylation levels, processing, and functionalities are poorly understood. Here, we report the identification and functional characterization of two Golgi-localized exo-beta-1,3-galactosidases from the glycosyl hydrolase 43 (GH43) family inArabidopsis thaliana. GH43 loss-of-function mutants exhibited root cell expansion defects in sugar-containing growth media. This root phenotype was associated with an increase in the extent of AGP cell wall association, as demonstrated by Yariv phenylglycoside dye quantification and comprehensive microarray polymer profiling of sequentially extracted cell walls. Characterization of recombinant GH43 variants revealed that the exo-beta-1,3-galactosidase activity of GH43 enzymes is hindered by beta-1,6 branches on beta-1,3-galactans. In line with this steric hindrance, the recombinant GH43 variants did not release galactose from cell wall-extracted glycoproteins or AGP-rich gum arabic. These results indicate that the lack of exo-beta-1,3-galactosidase activity alters cell wall extensibility in roots, a phenotype that could be explained by the involvement of galactosidases in AGP glycan biosynthesis.
22.	Niittylä, Totte (författare) Mobile forms of carbon in trees: metabolism and transport 2022 Ingår i: Tree Physiology. - : Oxford University Press (OUP). - 0829-318X .- 1758-4469. ; 42, s. 458–487- Forskningsöversikt (refereegranskat)abstract Plants constitute 80% of the biomass on earth, and almost two-thirds of this biomass is found in wood. Wood formation is a carbon (C)-demanding process and relies on C transport from photosynthetic tissues. Thus, understanding the transport process is of major interest for understanding terrestrial biomass formation. Here, we review the molecules and mechanisms used to transport and allocate C in trees. Sucrose is the major form in which C is transported in plants, and it is found in the phloem sap of all tree species investigated so far. However, in several tree species, sucrose is accompanied by other molecules, notably polyols and the raffinose family of oligosaccharides. We describe the molecules that constitute each of these transport groups, and their distribution across different tree species. Furthermore, we detail the metabolic reactions for their synthesis, the mechanisms by which trees load and unload these compounds in and out of the vascular system, and how they are radially transported in the trunk and finally catabolized during wood formation. We also address a particular C recirculation process between phloem and xylem that occurs in trees during the annual cycle of growth and dormancy. A search of possible evolutionary drivers behind the diversity of C-carrying molecules in trees reveals no consistent differences in C transport mechanisms between angiosperm and gymnosperm trees. Furthermore, the distribution of C forms across species suggests that climate-related environmental factors will not explain the diversity of C transport forms. However, the consideration of C-transport mechanisms in relation to tree-rhizosphere coevolution deserves further attention. To conclude the review, we identify possible future lines of research in this field.
23.	Niittylä, Totte (författare) Sucrose synthases are not involved in starch synthesis in Arabidopsis leaves 2022 Ingår i: Nature Plants. - : Springer Science and Business Media LLC. - 2055-026X .- 2055-0278. Tidskriftsartikel (refereegranskat)abstract Many plants accumulate transitory starch reserves in their leaves during the day to buffer their carbohydrate supply against fluctuating light conditions, and to provide carbon and energy for survival at night. It is universally accepted that transitory starch is synthesized from ADP-glucose (ADPG) in the chloroplasts. However, the consensus that ADPG is made in the chloroplasts by ADPG pyrophosphorylase has been challenged by a controversial proposal that ADPG is made primarily in the cytosol, probably by sucrose synthase (SUS), and then imported into the chloroplasts. To resolve this long-standing controversy, we critically re-examined the experimental evidence that appears to conflict with the consensus pathway. We show that when precautions are taken to avoid artefactual changes during leaf sampling, Arabidopsis thaliana mutants that lack SUS activity in mesophyll cells (quadruple sus1234) or have no SUS activity (sextuple sus123456) have wild-type levels of ADPG and starch, while ADPG is 20 times lower in the pgm and adg1 mutants that are blocked in the consensus chloroplastic pathway of starch synthesis. We conclude that the ADPG needed for starch synthesis in leaves is synthesized primarily by ADPG pyrophosphorylase in the chloroplasts.Mutant analysis shows that sucrose synthase makes no substantial contribution to transitory starch synthesis in Arabidopsis leaves, resolving a 20-year-old controversy about one of the most important pathways of photosynthetic metabolism.
24.	Nystedt, Björn, et al. (författare) The Norway spruce genome sequence and conifer genome evolution 2013 Ingår i: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 497:7451, s. 579-584 Tidskriftsartikel (refereegranskat)abstract Conifers have dominated forests for more than 200 million years and are of huge ecological and economic importance. Here we present the draft assembly of the 20-gigabase genome of Norway spruce (Picea abies), the first available for any gymnosperm. The number of well-supported genes (28,354) is similar to the >100 times smaller genome of Arabidopsis thaliana, and there is no evidence of a recent whole-genome duplication in the gymnosperm lineage. Instead, the large genome size seems to result from the slow and steady accumulation of a diverse set of long-terminal repeat transposable elements, possibly owing to the lack of an efficient elimination mechanism. Comparative sequencing of Pinus sylvestris, Abies sibirica, Juniperus communis, Taxus baccata and Gnetum gnemon reveals that the transposable element diversity is shared among extant conifers. Expression of 24-nucleotide small RNAs, previously implicated in transposable element silencing, is tissue-specific and much lower than in other plants. We further identify numerous long (>10,000 base pairs) introns, gene-like fragments, uncharacterized long non-coding RNAs and short RNAs. This opens up new genomic avenues for conifer forestry and breeding.
25.	Rende, Umut, et al. (författare) Cytosolic invertase contributes to the supply of substrate for cellulose biosynthesis in developing wood 2017 Ingår i: New Phytologist. - : Wiley-Blackwell. - 0028-646X .- 1469-8137. ; 214:2, s. 796-807 Tidskriftsartikel (refereegranskat)abstract Carbon for cellulose biosynthesis is derived from sucrose. Cellulose is synthesized from uridine 5'-diphosphoglucose (UDP-glucose), but the enzyme(s) responsible for the initial sucrose cleavage and the source of UDP-glucose for cellulose biosynthesis in developing wood have not been defined. We investigated the role of CYTOSOLIC INVERTASEs (CINs) during wood formation in hybrid aspen (Populus tremula × tremuloides) and characterized transgenic lines with reduced CIN activity during secondary cell wall biosynthesis. Suppression of CIN activity by 38–55% led to a 9–13% reduction in crystalline cellulose. The changes in cellulose were reflected in reduced diameter of acid-insoluble cellulose microfibrils and increased glucose release from wood upon enzymatic digestion of cellulose. Reduced CIN activity decreased the amount of the cellulose biosynthesis precursor UDP-glucose in developing wood, pointing to the likely cause of the cellulose phenotype. The findings suggest that CIN activity has an important role in the cellulose biosynthesis of trees, and indicate that cellulose biosynthesis in wood relies on a quantifiable UDP-glucose pool. The results also introduce a concept of altering cellulose microfibril properties by modifying substrate supply to cellulose biosynthesis.
26.	Rende, Umut, et al. (författare) Two-step derivatization for determination of sugar phosphates in plants by combined reversed phase chromatography/tandem mass spectrometry 2019 Ingår i: Plant Methods. - : Springer Science and Business Media LLC. - 1746-4811. ; 15 Tidskriftsartikel (refereegranskat)abstract Background Sugar phosphates are important intermediates of central carbon metabolism in biological systems, with roles in glycolysis, the pentose-phosphate pathway, tricarboxylic acid (TCA) cycle, and many other biosynthesis pathways. Understanding central carbon metabolism requires a simple, robust and comprehensive analytical method. However, sugar phosphates are notoriously difficult to analyze by traditional reversed phase liquid chromatography. Results Here, we show a two-step derivatization of sugar phosphates by methoxylamine and propionic acid anhydride after chloroform/methanol (3:7) extraction from Populus leaf and developing wood that improves separation, identification and quantification of sugar phosphates by ultra high performance liquid chromatography-electrospray ionization-mass spectrometry (UHPLC-ESI-MS). Standard curves of authentic sugar phosphates were generated for concentrations from pg to ng/mu l with a correlation coefficient R-2 > 0.99. The method showed high sensitivity and repeatability with relative standard deviation (RSD) < 20% based on repeated extraction, derivatization and detection. The analytical accuracy for Populus leaf extracts, determined by a two-level spiking approach of selected metabolites, was 79-107%. Conclusion The results show the reliability of combined reversed phase liquid chromatography-tandem mass spectrometry for sugar phosphate analysis and demonstrate the presence of two unknown sugar phosphates in Populus extracts.
27.	Roach, Melissa, et al. (författare) Fructokinase is required for carbon partitioning to cellulose in aspen wood 2012 Ingår i: The Plant Journal. - 0960-7412 .- 1365-313X. ; 70:6, s. 967-977 Tidskriftsartikel (refereegranskat)abstract Sucrose is the main transported form of carbon in several plant species, including Populus species. Sucrose metabolism in developing wood has therefore a central role in carbon partitioning to stem biomass. Half of the sucrose-derived carbon is in the form of fructose, but metabolism of fructose has received little attention as a factor in carbon partitioning to walls of wood cells. We show that RNAi-mediated reduction of FRK2 activity in developing wood of hybrid aspen (Populus tremula × tremuloides) led to the accumulation of soluble neutral sugars and a decrease in hexose phosphates and UDP-glucose, indicating that carbon flux to cell-wall polysaccharide precursors is decreased. Reduced FRK2 activity also led to thinner fiber cell walls with a reduction in the proportion of cellulose. No pleiotropic effects on stem height or diameter were observed. The results establish a central role for FRK2 activity in carbon flux to wood cellulose.
28.	Roach, Melissa, et al. (författare) Spatially resolved metabolic analysis reveals a central role for transcriptional control in carbon allocation to wood 2017 Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 68, s. 3529-3539 Tidskriftsartikel (refereegranskat)abstract The contribution of transcriptional and post-transcriptional regulation to modifying carbon allocation to developing wood of trees is not well defined. To clarify the role of transcriptional regulation, the enzyme activity patterns of eight central primary metabolism enzymes across phloem, cambium, and developing wood of aspen (Populus tremula L.) were compared with transcript levels obtained by RNA sequencing of sequential stem sections from the same trees. Enzymes were selected on the basis of their importance in sugar metabolism and in linking primary metabolism to lignin biosynthesis. Existing enzyme assays were adapted to allow measurements from similar to 1 mm(3) sections of dissected stem tissue. These experiments provided high spatial resolution of enzyme activity changes across different stages of wood development, and identified the gene transcripts probably responsible for these changes. In most cases, there was a clear positive relationship between transcripts and enzyme activity. During secondary cell wall formation, the increases in transcript levels and enzyme activities also matched with increased levels of glucose, fructose, hexose phosphates, and UDP-glucose, emphasizing an important role for transcriptional regulation in carbon allocation to developing aspen wood. These observations corroborate the efforts to increase carbon allocation to wood by engineering gene regulatory networks.
29.	Schneider, Rene, et al. (författare) Two Complementary Mechanisms Underpin Cell Wall Patterning during Xylem Vessel Development 2017 Ingår i: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 29:10, s. 2433-2449 Tidskriftsartikel (refereegranskat)abstract The evolution of the plant vasculature was essential for the emergence of terrestrial life. Xylem vessels are solute-transporting elements in the vasculature that possess secondary wall thickenings deposited in intricate patterns. Evenly dispersed microtubule (MT) bands support the formation of these wall thickenings, but how the MTs direct cell wall synthesis during this process remains largely unknown. Cellulose is the major secondary wall constituent and is synthesized by plasma membrane-localized cellulose synthases (CesAs) whose catalytic activity propels them through the membrane. We show that the protein CELLULOSE SYNTHASE INTERACTING1 (CSI1)/POM2 is necessary to align the secondary wall CesAs and MTs during the initial phase of xylem vessel development in Arabidopsis thaliana and rice (Oryza sativa). Surprisingly, these MT-driven patterns successively become imprinted and sufficient to sustain the continued progression of wall thickening in the absence of MTs and CSI1/POM2 function. Hence, two complementary principles underpin wall patterning during xylem vessel development.
30.	Sundell, David, et al. (författare) AspWood : High-Spatial-Resolution Transcriptome Profiles Reveal Uncharacterized Modularity of Wood Formation in Populus tremula 2017 Ingår i: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 29:7, s. 1585-1604 Tidskriftsartikel (refereegranskat)abstract Trees represent the largest terrestrial carbon sink and a renewable source of ligno-cellulose. There is significant scope for yield and quality improvement in these largely undomesticated species, and efforts to engineer elite varieties will benefit from improved understanding of the transcriptional network underlying cambial growth and wood formation. We generated high-spatial-resolution RNA sequencing data spanning the secondary phloem, vascular cambium, and wood-forming tissues of Populus tremula. The transcriptome comprised 28,294 expressed, annotated genes, 78 novel protein-coding genes, and 567 putative long intergenic noncoding RNAs. Most paralogs originating from the Salicaceae whole-genome duplication had diverged expression, with the exception of those highly expressed during secondary cell wall deposition. Coexpression network analyses revealed that regulation of the transcriptome underlying cambial growth and wood formation comprises numerous modules forming a continuum of active processes across the tissues. A comparative analysis revealed that a majority of these modules are conserved in Picea abies. The high spatial resolution of our data enabled identification of novel roles for characterized genes involved in xylan and cellulose biosynthesis, regulators of xylem vessel and fiber differentiation and lignification. An associated web resource (AspWood, http://aspwood.popgenie.org) provides interactive tools for exploring the expression profiles and coexpression network.
31.	Valerio, Concetta, et al. (författare) Laser Capture Microdissection Protocol for Xylem Tissues of Woody Plants 2017 Ingår i: Frontiers in Plant Science. - : Frontiers Media SA. - 1664-462X. ; 7 Tidskriftsartikel (refereegranskat)abstract Laser capture microdissection (LCM) enables precise dissection and collection of individual cell types from complex tissues. When applied to plant cells, and especially to woody tissues, LCM requires extensive optimization to overcome such factors as rigid cell walls, large central vacuoles, intercellular spaces, and technical issues with thickness and flatness of the sections. Here we present an optimized protocol for the laser-assisted microdissection of developing xylem from mature trees: a gymnosperm (Norway spruce, Picea abies) and an angiosperm (aspen, Populus tremula) tree. Different cell types of spruce and aspen wood (i.e., ray cells, tracheary elements, and fibers) were successfully microdissected from tangential, cross and radial cryosections of the current years growth ring. Two approaches were applied to achieve satisfactory flatness and anatomical integrity of the spruce and aspen specimens. The commonly used membrane slides were ineffective as a mounting surface for the wood cryosections. Instead, in the present protocol we use glass slides, and introduce a glass slide sandwich assembly for the preparation of aspen sections. To ascertain that not only the anatomical integrity of the plant tissue, but also the molecular features were not compromised during the whole LCM procedure, good quality total RNA could be extracted from the microdissected cells. This showed the efficiency of the protocol and established that our methodology can be integrated in transcriptome analyses to elucidate cell-specific molecular events regulating wood formation in trees.
32.	Wang, Wei, et al. (författare) Aspen growth is not limited by starch reserves 2022 Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 32, s. 3619-3627 Tidskriftsartikel (refereegranskat)abstract All photosynthetic organisms balance CO2 assimilation with growth and carbon storage. Stored carbon is used for growth at night and when demand exceeds assimilation. Gaining a mechanistic understanding of carbon partitioning between storage and growth in trees is important for biological studies and for estimating the potential of terrestrial photosynthesis to sequester anthropogenic CO2 emissions.(1,2) Starch represents the main carbon storage in plants.(3,4) To examine the carbon storage mechanism and role of starch during tree growth, we generated and characterized low-starch hybrid aspen (Populus tremula x tremuloides) trees using CRISPR-Cas9-mediated gene editing of two PHOSPHOGLUCOMUTASE (PGM) genes coding for plastidial PGM isoforms essential for starch biosynthesis. We demonstrate that starch deficiency does not reduce tree growth even in short days, showing that starch is not a critical carbon reserve during diel growth of aspen. The low-starch trees assimilated up to similar to 30% less CO2 compared to the wild type under a range of irradiance levels, but this did not reduce growth or wood density. This implies that aspen growth is not limited by carbon assimilation under benign growth conditions. Moreover, the timing of bud set and bud flush in the low-starch trees was not altered, implying that starch reserves are not critical for the seasonal growth-dormancy cycle. The findings are consistent with a passive starch storage mechanism that contrasts with the annual Arabidopsis and indicate that the capacity of the aspen to absorb CO2 is limited by the rate of sink tissue growth.
33.	Wang, Wei, et al. (författare) OPENER Is a Nuclear Envelope and Mitochondria Localized Protein Required for Cell Cycle Progression in Arabidopsis 2019 Ingår i: Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 31, s. 1446-1465 Tidskriftsartikel (refereegranskat)abstract Currently one-third of the proteins encoded by the Arabidopsis (Arabidopsis thaliana) genome are of unknown function. Some of these unknown proteins are likely to be involved in uncharacterized vital biological processes. Evolutionarily conserved single copy genes in flowering plants have been shown to be enriched in essential housekeeping functions. This together with publicly available gene expression data allows for a focused search for uncharacterized essential genes. Here we identify an essential single copy gene called OPENER (OPNR) in Arabidopsis. We show that OPNR is predominantly expressed in actively dividing cells and performs essential functions in seed development and root meristem maintenance. Cell cycle tracking using 5-ethynyl-2'-deoxyuridine staining and fluorescent cell cycle markers together with the increased size of nucleolus and nucleus in opnr mutants indicate that OPNR is required for cell cycle progression through the S or G2 phases. Intriguingly, OPNR localizes to the nuclear envelope and mitochondria. Furthermore, the nuclear envelope localization of OPNR is dependent on its interaction with nuclear inner membrane Sad1/UNC-84 (SUN) domain proteins SUN1 and SUN2. Taken together our results open a line of investigation into an evolutionarily conserved essential cellular process occurring in both the nuclear envelopes and mitochondria of dividing cells.
34.	Wang, Wei, et al. (författare) Sucrose synthase activity is not required for cellulose biosynthesis in Arabidopsis 2022 Ingår i: Plant Journal. - : Wiley. - 0960-7412 .- 1365-313X. ; 110, s. 1493-1497 Tidskriftsartikel (refereegranskat)abstract Biosynthesis of plant cell walls requires UDP-glucose as the substrate for cellulose biosynthesis, and as an intermediate for the synthesis of other matrix polysaccharides. The sucrose cleaving enzyme sucrose synthase (SUS) is thought to have a central role in UDP-glucose biosynthesis, and a long-held and much debated hypothesis postulates that SUS is required to supply UDP-glucose to cellulose biosynthesis. To investigate the role of SUS in cellulose biosynthesis of Arabidopsis thaliana we characterized mutants in which four or all six Arabidopsis SUS genes were disrupted. These sus mutants showed no growth phenotypes, vascular tissue cell wall defects, or changes in cellulose content. Moreover, the UDP-glucose content of rosette leaves of the sextuple sus mutants was increased by approximately 20% compared with wild type. It can thus be concluded that cellulose biosynthesis is able to employ alternative UDP-glucose biosynthesis pathway(s), and thereby the model of SUS requirements for cellulose biosynthesis in Arabidopsis can be refuted.
35.	Wessels, Bernard, 1985- (författare) The significance of ethylene and ethylene response factors in wood formation of hybrid aspen 2018 Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract The woody tissues serve to stabilise plants, store nutrients and translocate water and minerals. The formation of wood, or ’secondary xylem’, follows a well-defined developmental gradient which is initiated by cell division activity in the vascular cambium. The ’xylem cambial derivatives’ then expand before deposition of the secondary cell wall (SCW), which is where most of the biomass of wood originates. After this, some cells of the xylem typically undergo programmed cell death (PCD). Cellulose and lignin are chemical components of the SCW that provide structural support and water impermeability, respectively. The chemical composition of the SCWs is also important economically since it affects the efficiency of wood processing during pulping and enzymatic hydrolysis. Two dominant xylem cell types of angiosperm tree species like Populus are the fibers and the vessel elements. Fibers are important for the mechanical strength of the wood and provide the majority of the wood biomass. Vessel elements join endwise to form hollow tubes, or vessels, for the purposes of water and solute transport in the stem. Formation of wood is a complex process, subject to multiple levels of regulation. Plant hormones are important for wood formation, and ethylene signalling has been shown to stimulate cambial activity, affect the ratio between fibers and vessel elements, as well as the expansion of the cambial derivatives. Ethylene is also involved in the ‘tension wood’ response of stems that are displaced from their original vertical position. Formation of ’tension wood’ generates a force that lifts the stem back to the upright growing position. What remains unknown is the molecular link between ethylene signalling and wood formation. The work in this thesis focuses on providing this link using the model tree species hybrid aspen (Populus tremula x tremuloides). Using a state-of-the-art transcriptomic database that spans all phases of xylem differentiation in hybrid aspen wood, from cell division through xylem cell expansion to xylem maturation (SCW deposition and PCD), the expression of the ethylene pathway related genes was investigated during normal wood formation. The analyses reveal ethylene perception and transcriptional reprogramming is possible across all zones of wood formation. Previously uncharacterised components were identified that may be important contributors to wood formation. Furthermore, although ethylene is known to affect the ratio between the abundance of the vessel elements and the fibers, genetic evidence is lacking. Using the tension wood response and transgenic trees modified in ethylene signalling, it was shown that ethylene is a negative regulator of vessel formation and important for a functional tension wood response. Furthermore, characterisation of two transcription factors (TFs), belonging to the ethylene response factor (ERF) gene family, suggests that aspects of xylem cell division, expansion and subsequent SCW formation, including lignification, can be affected by ERF85 and ERF139 in an ethylene-dependent manner. Phase transitions during wood formation need to be controlled spatiotemporally, and transcriptional regulation by these ERFs seems to be part of such control to establish correct transitions between cell expansion, secondary cell wall formation and lignification. The work presented here also identifies promising additions to the toolkit available for forest tree biotechnology and molecular breeding programmes.
36.	Xue, Weiya, et al. (författare) Paramutation-like interaction of T-DNA loci in arabidopsis 2012 Ingår i: PLOS ONE. - : Public library of science. - 1932-6203. ; 7:12, s. e51651- Tidskriftsartikel (refereegranskat)abstract In paramutation, epigenetic information is transferred from one allele to another to create a gene expression state which is stably inherited over generations. Typically, paramutation describes a phenomenon where one allele of a gene down-regulates the expression of another allele. Paramutation has been described in several eukaryotes and is best understood in plants. Here we describe an unexpected paramutation-like trans SALK T-DNA interaction in Arabidopsis. Unlike most of the previously described paramutations, which led to gene silencing, the trans SALK T-DNA interaction caused an increase in the transcript levels of the endogenous gene (COBRA) where the T-DNA was inserted. This increased COBRA expression state was stably inherited for several generations and led to the partial suppression of the cobra phenotype. DNA methylation was implicated in this trans SALK T-DNA interaction since mutation of the DNA methyltransferase 1 in the suppressed cobra caused a reversal of the suppression. In addition, null mutants of the DNA demethylase ROS1 caused a similar COBRA transcript increase in the cobra SALK T-DNA mutant as the trans T-DNA interaction. Our results provide a new example of a paramutation-like trans T-DNA interaction in Arabidopsis, and establish a convenient hypocotyl elongation assay to study this phenomenon. The results also alert to the possibility of unexpected endogenous transcript increase when two T-DNAs are combined in the same genetic background. Citation: Xue W, Ruprecht C, Street N, Hematy K, Chang C, et al. (2012) Paramutation-Like Interaction of T-DNA Loci in Arabidopsis. PLoS ONE 7(12): e51651. doi:10.1371/journal.pone.0051651
37.	Zhang, Xueyang, et al. (författare) Cellulose Synthase Stoichiometry in Aspen Differs from Arabidopsis and Norway Spruce 2018 Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 177, s. 1096-1107 Tidskriftsartikel (refereegranskat)abstract Cellulose is synthesized at the plasma membrane by cellulose synthase complexes (CSCs) containing cellulose synthases (CESAs). Genetic analysis and CESA isoform quantification indicate that cellulose in the secondary cell walls of Arabidopsis (Arabidopsis thaliana) is synthesized by isoforms CESA4, CESA7, and CESA8 in equimolar amounts. Here, we used quantitative proteomics to investigate whether the CSC model based on Arabidopsis secondary cell wall CESA stoichiometry can be applied to the angiosperm tree aspen (Populus tremula) and the gymnosperm tree Norway spruce (Picea abies). In the developing xylem of aspen, the secondary cell wall CESA stoichiometry was 3:2:1 for PtCESA8a/b:PtCESA4:PtCESA7a/b, while in Norway spruce, the stoichiometry was 1:1:1, as observed previously in Arabidopsis. Furthermore, in aspen tension wood, the secondary cell wall CESA stoichiometry changed to 8:3:1 for PtCESA8a/b:PtCESA4:PtCESA7a/b. PtCESA8b represented 73% of the total secondary cell wall CESA pool, and quantitative polymerase chain reaction analysis of CESA transcripts in cryosectioned tension wood revealed increased PtCESA8b expression during the formation of the cellulose-enriched gelatinous layer, while the transcripts of PtCESA4, PtCESA7a/b, and PtCESA8a decreased. A wide-angle x-ray scattering analysis showed that the shift in CESA stoichiometry in tension wood coincided with an increase in crystalline cellulose microfibril diameter, suggesting that the CSC CESA composition influences microfibril properties. The aspen CESA stoichiometry results raise the possibility of alternative CSC models and suggest that homomeric PtCESA8b complexes are responsible for cellulose biosynthesis in the gelatinous layer in tension wood.

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