Molecular probes are required to detect cell wall polymers in-situ to aid understanding of their cell biology and several studies have shown that cell wall epitopes have restricted occurrences across sections of plant organs indicating that cell wall structure is highly developmentally regulated. Xyloglucan is the major hemicellulose or cross-linking glycan of the primary cell walls of dicotyledons although little is known of its occurrence or functions in relation to cell development and cell wall microstructure. Using a neoglycoprotein approach, in which a XXXG heptasaccharide of tamarind seed xyloglucan was coupled to BSA to produce an immunogen, we have generated a rat monoclonal antibody (designated LM15) to the XXXG structural motif of xyloglucans. The specificity of LM15 has been confirmed by the analysis of LM15 binding using glycan microarrays and oligosaccharide hapten inhibition of binding studies. The use of LM15 for the analysis of xyloglucan in the cell walls of tamarind and nasturtium seeds, in which xyloglucan occurs as a storage polysaccharide, indicated that the LM15 xyloglucan epitope occurs throughout the thickened cell walls of the tamarind seed and in the outer regions, adjacent to middle lamellae, of the thickened cell walls of the nasturtium seed. Immunofluorescence analysis of LM15 binding to sections of tobacco and pea stem internodes indicated that the xyloglucan epitope was restricted to a few cell types in these organs. Enzymatic removal of pectic homogalacturonan from equivalent sections resulted in the abundant detection of distinct patterns of the LM15 xyloglucan epitope across these organs and a diversity of occurrences in relation to the cell wall microstructure of a range of cell types. These observations support ideas that xyloglucan is associated with pectin in plant cell walls. They also indicate that documented patterns of cell wall epitopes in relation to cell development and cell differentiation may need to be re-considered in relation to the potential masking of cell wall epitopes by other cell wall components.

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Pectic homogalacturonan masks abundant sets of xyloglucan epitopes in plant cell walls

High-resolution, three-dimensional structures of the archetypal glycoside hydrolase family 16 (GH16) endo-xyloglucanases Tm-NXG1 and Tm-NXG2 from nasturtium (Tropaeolum majus) have been solved by x-ray crystallography Key structural features that modulate the relative rates of substrate hydrolysis to transglycosylation in the GH16 xyloglucan-active enzymes were identified by structure–function studies of the recombinantly expressed enzymes in comparison with data for the strict xyloglucan endo-transglycosylase Ptt-XET16-34 from hybrid aspen (Populus tremula × Populus tremuloides) Production of the loop deletion variant Tm-NXG1-ΔYNIIG yielded an enzyme that was structurally similar to Ptt-XET16-34 and had a greatly increased transglycosylation:hydrolysis ratio Comprehensive bioinformatic analyses of XTH gene products, together with detailed kinetic data, strongly suggest that xyloglucanase activity has evolved as a gain of function in an ancestral GH16 XET to meet specific biological requirements during seed germination, fruit ripening, and rapid wall expansion

/pdf/structural-evidence-for-the-evolution-of-xyloglucanase-3mhcvu244h.pdf

Structural Evidence for the Evolution of Xyloglucanase Activity from Xyloglucan Endo-Transglycosylases: Biological Implications for Cell Wall Metabolism

Hydro-responsive plant movements have provided inspiration for the design of adaptive materials. Harrington et al. investigate the hydration-dependent unfolding of ice plant seed capsules and find an origami-like folding pattern, which could aid the development of biomimetic folding structures.

/pdf/origami-like-unfolding-of-hydro-actuated-ice-plant-seed-8g4psmzzju.pdf

Origami-like unfolding of hydro-actuated ice plant seed capsules

Wood cell walls: biosynthesis, developmental dynamics and their implications for wood properties.

Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.

/pdf/tensional-stress-generation-in-gelatinous-fibres-a-review-1bk61b5a22.pdf

Tensional stress generation in gelatinous fibres: a review and possible mechanism based on cell-wall structure and composition

Tension wood is a specialized tissue of deciduous trees that functions in bending woody stems to optimize their position in space. Tension wood fibers that develop on one side of the stem have an increased potency to shrink compared with fibers on the opposite side, thus creating a bending moment. It is believed that the gelatinous (G) cell wall layer containing almost pure cellulose of tension wood fibers is pivotal to their shrinking. By analyzing saccharide composition and linkage in isolated G-layers of poplar, we found that they contain some matrix components in addition to cellulose, of which xyloglucan is the most abundant. Xyloglucan, xyloglucan endo-transglycosylase (XET) activity and xyloglucan endo-transglycosylase/hydrolase (XTH) gene products were detected in developing G-layers by labeling using CCRC-M1 monoclonal antibody, in situ incorporation of XXXG-SR and the polyclonal antibody to poplar PttXET16-34, respectively, indicating that xyloglucan is incorporated into the G-layer during its development. Moreover, several XTH transcripts were altered and were generally up-regulated in developing tension wood compared with normal wood. In mature G-fibers, XTH gene products were detected in the G-layers while the XET activity was evident in the adjacent S 2 wall layer. We propose that XET activity is essential for G-fiber shrinking by repairing xyloglucan cross-links between G- and S 2 -layers and thus maintaining their contact. Surprisingly, XTH gene products and XET activity persisted in mature G-fibers for several years, suggesting that the enzyme functions after cell death repairing the cross-links as they are being broken during the shrinking process.

/pdf/xyloglucan-endo-transglycosylase-xet-functions-in-gelatinous-2j4dyo0eid.pdf

Xyloglucan Endo-transglycosylase (XET) Functions in Gelatinous Layers of Tension Wood Fibers in Poplar—A Glimpse into the Mechanism of the Balancing Act of Trees

Tatsuya Awano

Papers

Xyloglucan Endo-transglycosylase (XET) Functions in Gelatinous Layers of Tension Wood Fibers in Poplar—A Glimpse into the Mechanism of the Balancing Act of Trees