| 1. |
- Mahboubi, Miramirhossein, et al.
(författare)
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Aspen SUCROSE TRANSPORTER3 Allocates Carbon into Wood Fibers
- 2013
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 163, s. 1729-1740
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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.
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| 2. |
- Mahboubi, Miramirhossein, et al.
(författare)
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C-13 Tracking after (CO2)-C-13 Supply Revealed Diurnal Patterns of Wood Formation in Aspen
- 2015
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 168, s. 478-489
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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.
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| 3. |
- Mahboubi, Miramirhossein, et al.
(författare)
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Sucrose transport and carbon fluxes during wood formation
- 2018
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 164, s. 67-81
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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.
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| 4. |
- Mahboubi, Miramirhossein
(författare)
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New insights into carbon transport and incorporation to wood
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood formation in trees requires carbon import from the photosynthetic tissues. In several tree species the majority of this carbon is derived from sucrose transported in the phloem. This thesis describes experimental work on the mechanism of radial sucrose transport from phloem to developing wood and subsequent incorporation of carbon into wood polymers. I investigated the role of active sucrose transport during secondary cell wall formation in hybrid aspen (Populus tremula x tremuloides). Reduction of a plasma membrane localised sucrose transporter (PttSUT3) decreased carbon allocation to secondary walls of wood fibers. The results show the importance of active sucrose transport for wood formation in a symplasmic phloem loading tree species, and identify PttSUT3 as a principal transporter for carbon delivery into secondary cell wall forming wood fibers. To investigate the temporal dynamics of carbon transport and wood polymer biosynthesis, I labelled two-month-old hybrid aspen trees with ¹³CO₂ and tracked the flux of ¹³C from leaves to developing wood. Analysis of the cell wall polymer labelling patterns using 2D-NMR revealed temporal differences in the labelling of carbohydrates and lignin subunits. Further analysis showed that ¹³C incorporation into different wood polymers is influenced by the diurnal cycle. Primary metabolism enzymes in the developing wood play an important role in carbon partitioning to wood cell wall polymers. In this part of the study, the activity of eight primary metabolism enzymes linking sucrose to cell wall precursor biosynthesis was determined in phloem, cambium and in different stages of wood development. Comparison of enzyme activity measurements with transcript and metabolite profiles across the developing wood suggested a central role for transcriptional regulation of carbon allocation to wood. Combined, the results of the three projects provide new insights into the mechanism and regulation of carbon allocation to developing wood.
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| 5. |
- Roach, Melissa, et al.
(författare)
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Spatially resolved metabolic analysis reveals a central role for transcriptional control in carbon allocation to wood
- 2017
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Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 68, s. 3529-3539
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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.
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