Structure of the xyloglucan produced by suspension-cultured tomato cells.
ABSTRACT The xyloglucan secreted by suspension-cultured tomato (Lycopersicon esculentum) cells was structurally characterized by analysis of the oligosaccharides generated by treating the polysaccharide with a xyloglucan-specific endoglucanase (XEG). These oligosaccharide subunits were chemically reduced to form the corresponding oligoglycosyl alditols, which were isolated by high-performance liquid chromatography (HPLC). Thirteen of the oligoglycosyl alditols were structurally characterized by a combination of matrix-assisted laser-desorption ionization mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. Nine of the oligoglycosyl alditols (GXGGol, XXGGol, GSGGol, XSGGol, LXGGol, XTGGol, LSGGol, LLGGol, and LTGGol, [see, Fry, S.C.; York, W.S., et al., Physiologia Plantarum 1993, 89, 1-3, for this nomenclature]) are derived from oligosaccharide subunits that have a cellotetraose backbone. Very small amounts of oligoglycosyl alditols (XGGol, XGGXXGGol, XXGGXGGol, and XGGXSGGol) derived from oligosaccharide subunits that have a cellotriose or celloheptaose backbone were also purified and characterized. The results demonstrate that the xyloglucan secreted by suspension-cultured tomato cells is very complex and is composed predominantly of 'XXGG-type' subunits with a cellotetraose backbone. The rigorous characterization of the oligoglycosyl alditols and assignment of their 1H and 13C NMR spectra constitute a robust data set that can be used as the basis for rapid and accurate structural profiling of xyloglucans produced by Solanaceous plant species and the characterization of enzymes involved in the synthesis, modification, and breakdown of these polysaccharides.
Article: Hemicellulose biosynthesis.[Show abstract] [Hide abstract]
ABSTRACT: One major component of plant cell walls is a diverse group of polysaccharides, the hemicelluloses. Hemicelluloses constitute roughly one-third of the wall biomass and encompass the heteromannans, xyloglucan, heteroxylans, and mixed-linkage glucan. The fine structure of these polysaccharides, particularly their substitution, varies depending on the plant species and tissue type. The hemicelluloses are used in numerous industrial applications such as food additives as well as in medicinal applications. Their abundance in lignocellulosic feedstocks should not be overlooked, if the utilization of this renewable resource for fuels and other commodity chemicals becomes a reality. Fortunately, our understanding of the biosynthesis of the various hemicelluloses in the plant has increased enormously in recent years mainly through genetic approaches. Taking advantage of this knowledge has led to plant mutants with altered hemicellulosic structures demonstrating the importance of the hemicelluloses in plant growth and development. However, while we are on a solid trajectory in identifying all necessary genes/proteins involved in hemicellulose biosynthesis, future research is required to combine these single components and assemble them to gain a holistic mechanistic understanding of the biosynthesis of this important class of plant cell wall polysaccharides.Planta 06/2013; · 3.35 Impact Factor
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ABSTRACT: The present study aimed at analyzing the structural features of seed mucilage and cell-wall polysaccharides which accounted for 41% of the mass of flax meal (FM). A combination of high molar-mass mucilage-like polysaccharides (rhamnogalacturonan and arabinoxylan) was released from FM in water, together with arabinogalactan proteins and glucans. About half of FM homogalacturonans was extracted using a calcium chelator and boiling water. Hemicellulosic xyloglucans and xylans were further extracted with 1M KOH, in ∼13% FM-sugars yield. Structural characterization of the xyloglucan using specific enzyme hydrolysis, ion exchange chromatography (HPAEC) and matrix assisted laser desorption ionization-time-of-flight (MALDI-TOF) mass spectroscopy showed the presence of XXXG type xyloglucan, but also that of XXGG-structure, possibly characteristic of flax seeds. Hydrolysis of xylans with endo-(1→4)-β-d-xylanase, and analysis of the neutral and acidic oligosaccharides by MALDI-TOF-MS showed that xylan consisted of β-(1→4)-linked-d-xylopyranose backbone with some zones (DP 5-7) substituted with 4-O-MeGlcA\GlcA\Glc residues.Carbohydrate polymers. 04/2013; 93(2):651-60.
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ABSTRACT: Xyloglucan is the dominant hemicellulose present in the primary cell walls of dicotyledonous plants. Unlike Arabidopsis xyloglucan, which contains galactosyl and fucosyl-substituents, tomato (Solanum lycopersicum) xyloglucan contains arabinofuranosyl-residues. To investigate the biological function of these differing substituents we used a functional complementation approach. Candidate glycosyltransferases were identified from tomato by using comparative genomics with known xyloglucan galactosyltransferase genes from Arabidopsis. These candidate genes were expressed in an Arabidopsis mutant lacking xyloglucan galactosylation and two of them resulted in the production of arabinosylated xyloglucan, a structure not previously found in this plant species. These genes may therefore encode xyloglucan arabinofuranosyltransferases. Moreover, the addition of arabinofuranosyl-residues to the xyloglucan of this Arabidopsis mutant rescued a growth and cell wall biomechanics phenotype, demonstrating that the function of xyloglucan in plant growth, development and mechanics has considerable flexibility in terms of the specific residues in the side chains. These experiments also highlight the potential of re-engineering the sugar substituents on plant wall polysaccharides without compromising growth or viability.Plant physiology 07/2013; · 6.56 Impact Factor