42 research outputs found
Enzymically attaching oligosaccharide-linked âcargoesâ to cellulose and other commercial polysaccharides via stable covalent bonds
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Hetero-trans-β-glucanase, an enzyme unique to Equisetum plants, functionalises cellulose
Cell walls are metabolically active components of plant cells. They contain diverse enzymes, including transglycanases (endotransglycosylases), enzymes that âcut and pasteâ certain structural polysaccharide molecules and thus potentially remodel the wall during growth and development. Known transglycanase activities modify several cellâwall polysaccharides (xyloglucan, mannans, mixedâlinkage βâglucan and xylans); however, no transglycanases were known to act on cellulose, the principal polysaccharide of biomass. We now report the discovery and characterization of heteroâtransâβâglucanase (HTG), a transglycanase that targets cellulose, in horsetails (Equisetum spp., an earlyâdiverging genus of monilophytes). HTG is also remarkable in predominantly catalysing heteroâtransglycosylation: its preferred donor substrates (cellulose or mixedâlinkage βâglucan) differ qualitatively from its acceptor substrate (xyloglucan). HTG thus generates stable celluloseâxyloglucan and mixedâlinkage βâglucanâxyloglucan covalent bonds, and may therefore strengthen ageing Equisetum tissues by interâlinking different structural polysaccharides of the cell wall. 3D modelling suggests that only three key amino acid substitutions (Trp â Pro, Gly â Ser and Arg â Leu) are responsible for the evolution of HTG's unique specificity from the betterâknown xyloglucanâacting homoâtransglycanases (xyloglucan endotransglucosylase/hydrolases; XTH). Among land plants, HTG appears to be confined to Equisetum, but its target polysaccharides are widespread, potentially offering opportunities for enhancing crop mechanical properties, such as wind resistance. In addition, by linking cellulose to xyloglucan fragments previously tagged with compounds such as dyes or indicators, HTG may be useful biotechnologically for manufacturing stably functionalized celluloses, thereby potentially offering a commercially valuable âgreenâ technology for industrially manipulating biomass
Developmental features of cotton fibre middle lamellae in relation to cell adhesion and cell detachment in cultivars with distinct fibre qualities.
Background: Cotton fibre quality traits such as fibre length, strength, and degree of maturation are determined by genotype and environment during the sequential phases of cotton fibre development (cell elongation, transition to secondary cell wall construction and cellulose deposition). The cotton fibre middle lamella (CFML) is crucial for both cell adhesion and detachment processes occurring during fibre development. To explore the relationship between fibre quality and the pace at which cotton fibres develop, a structural and compositional analysis of the CFML was carried out in several cultivars with different fibre properties belonging to four commercial species: Gossypium hirsutum, G. barbadense, G. herbaceum and G. arboreum. Results: Cotton fibre cell adhesion, through the cotton fibre middle lamella (CFML), is a developmentally regulated process determined by genotype. The CFML is composed of de-esterified homogalacturonan, xyloglucan and arabinan in all four fibre-producing cotton species: G. hirsutum, G. barbadense, G. herbaceum and G. arboreum. Conspicuous paired cell wall bulges are a feature of the CFML of two G. hirsutum cultivars from the onset of fibre cell wall detachment to the start of secondary cell wall deposition. Xyloglucan is abundant in the cell wall bulges and in later stages pectic arabinan is absent from these regions. Conclusions: The CFML of cotton fibres is re-structured during the transition phase. Paired cell wall bulges, rich in xyloglucan, are significantly more evident in the G. hirsutum cultivars than in other cotton species
Expression of tobacco necrosis virus open reading frames 1 and 2 is sufficient for the replication of satellite tobacco necrosis virus
AbstractTobacco necrosis virus (TNV) is a small icosahedral plant virus which is often associated with satellite viruses. The genomic RNA of TNV contains six open reading frames (ORFs), of which ORFs 1 and 2 are thought to encode the viral polymerase. We demonstrate that tobacco protoplasts transfected with a vector containing TNV ORFs 1 and 2 under the control of the cauliflower mosaic virus 35S promoter, as well as protoplasts derived from transgenic Nicotiana tabacum containing the same gene(s), support replication of satellite tobacco necrosis virus RNA