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South Australian Node:
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Wine Innovation Central
THE UNIVERSITY OF ADELAIDE
Urrbrae SA 5064

Victorian Node:
Plant Cell Biology Research Centre
School of Botany
THE UNIVERSITY OF MELBOURNE
Parkville VIC 3010

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Queensland Alliance for Agriculture & Food Innovation
John Hines Building
THE UNIVERSITY OF QUEENSLAND
St Lucia QLD 4072 

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Abstracts

  • Burton, RA; Gidley, MJ; Fincher, GB (2010). Heterogeneity in the chemistry, structure and function of plant cell walls. Nature Chemical Biology, 6 (10): 724-732

Higher plants resist the forces of gravity and powerful lateral forces through the cumulative strength of the walls that surround individual cells. These walls consist mainly of cellulose, noncellulosic polysaccharides and lignin, in proportions that depend upon the specific functions of the cell and its stage of development. Spatially and temporally controlled heterogeneity in the physicochemical properties of wall polysaccharides is observed at the tissue and individual cell levels, and emerging in situ technologies are providing evidence that this heterogeneity also occurs across a single cell wall. We consider the origins of cell wall heterogeneity and identify contributing factors that are inherent in the molecular mechanisms of polysaccharide biosynthesis and are crucial for the changing biological functions of the wall during growth and development. We propose several key questions to be addressed in cell wall biology, together with an alternative two-phase model for the assembly of noncellulosic polysaccharides in plants [Full Text]

  • Rachel A. Burton, Helen M. Collins, Natalie A. J. Kibble, Jessica A. Smith, Neil J. Shirley, Stephen A. Jobling, Marilyn Henderson, Rohan R. Singh, Filomena Pettolino, Sarah M. Wilson, Anthony R. Bird, David L. Topping, Antony Bacic and Geoffrey B. Fincher (2011). Over-expression of specific HvCslF cellulose synthase-like genes in transgenic barley increases the levels of cell wall (1,3;1,4)-β-d-glucans and alters their fine structure. Plant Biotechnology Journal, 9 (2): 117-135

 

 

Cell walls in commercially important cereals and grasses are characterized by the presence of (1,3;1,4)-β-D-glucans. These polysaccharides are beneficial constituents of human diets, where they can reduce the risk of hypercholesterolemia, type II diabetes, obesity and colorectal cancer. The biosynthesis of cell wall (1,3;1,4)-β-D-glucans in the Poaceae is mediated, in part at least, by the cellulose synthase-like CslF family of genes. Over-expression of the barley CslF6 gene under the control of an endosperm-specific oat globulin promoter results in increases of more than 80% in (1,3;1,4)-β-D-glucan content in grain of transgenic barley. Analyses of (1,3;1,4)-β-D-glucan fine structure indicate that individual CslF enzymes might direct the synthesis of (1,3;1,4)-β-D-glucans with different structures. When expression of the CslF6 transgene is driven by the Pro35S promoter, the transgenic lines have up to sixfold higher levels of (1,3;1,4)-β-D-glucan in leaves, but similar levels as controls in the grain. Some transgenic lines of Pro35S:CslF4 also show increased levels of (1,3;1,4)-β-D-glucans in grain, but not in leaves. Thus, the effects of CslF genes on (1,3;1,4)-β-D-glucan levels are dependent not only on the promoter used, but also on the specific member of the CslF gene family that is inserted into the transgenic barley lines. Altering (1,3;1,4)-β-D-glucan levels in grain and vegetative tissues will have potential applications in human health, where (1,3;1,4)-β-D-glucans contribute to dietary fibre, and in tailoring the composition of biomass cell walls for the production of bioethanol from cereal crop residues and grasses. [Full Text]

  • Collins, HM; Burton, RA; Topping, DL; Liao, ML; Bacic, A; Fincher, GB (2010). Variability in Fine Structures of Noncellulosic Cell Wall Polysaccharides from Cereal Grains: Potential Importance in Human Health and Nutrition. Cereal Chemistry, 87 (4):272-282

Noncellulosic polysaccharides from the cell walls of cereal grains are not digested by human small intestinal enzymes and so contribute to total dietary fiber intake. These polysaccharides are becoming recognized increasingly for their potential to lower the risk of serious diet-related conditions such as type H diabetes, cardiovascular disease, colorectal cancer, and diverticular disease. The effectiveness of noncellulosic cell wall polysaccharides in improving health outcomes is related to the fine structure and associated physicochemical properties. The two most nutritionally relevant wall polysaccharides of cereal grains are the arabinoxylans and the (1-3,1-4)-beta-D-glucans. These polysaccharides have high molecular mass values but are nevertheless soluble in aqueous media, at least in part, where they adopt highly asymmetrical conformations and consequently form high viscosity solutions. Thus, arabinoxylans and (1-3,1-4)-beta-D-glucans contribute to the soluble fiber component of human diets. The molecular size, solubility, and viscosity of the polysaccharides vary widely not only between different cereals but also within a single species. The variability in these properties reflects differences in the chemical structure of the polysaccharides, which in turn influences the beneficial effects of arabinoxylans and (1-3,1-4)-beta-D-glucans in human diets. Here, we summarize information on the variability of fine structures of the arabinoxylans and (1-3,1-4)-beta-D-glucans in common cereals and relate these to solubility, viscosity, and health benefits. The recent identification of genes involved in the biosynthesis of the (1-3,1-4)-beta-D-glucans opens the way for the genetic improvement of cereal quality parameters that are important in human health [Full Text]

  • Burton, RA; Fincher, GB (2009) (1,3;1,4)-beta-D-Glucans in Cell Walls of the Poaceae, Lower Plants, and Fungi: A Tale of Two Linkages. Molecular Plant, 2 (5): 873-882


1,3;1,4)-beta-D-Glucans consist of unbranched and unsubstituted chains of (1,3)- and (1,4)-beta-glucosyl residues, in which the ratio of (1,4)-beta-D-glucosyl residues to (1,3)-beta-D-glucosyl residues appears to influence not only the physicochemical properties of the polysaccharide and therefore its functional properties in cell walls, but also its adoption by different plant species during evolution. The (1,3;1,4)-beta-D-glucans are widely distributed as non-cellulosic matrix phase polysaccharides in cell walls of the Poaceae, which evolved relatively recently and consist of the grasses and commercially important cereal species, but they are less commonly found in lower vascular plants, such as the horsetails, in algae and in fungi. The (1,3;1,4)-beta-D-glucans have often been considered to be components mainly of primary cell walls, but recent observations indicate that they can also be located in secondary walls of certain tissues. Enzymes involved in the depolymerisation of (1,3;1,4)-beta-D-glucans have been well characterized. In contrast, initial difficulties in purifying the enzymes responsible for (1,3;1,4)-beta-D-glucan biosynthesis slowed progress in the identification of the genes that encode (1,3;1,4)-beta-D-glucan synthases, but emerging comparative genomics and associated techniques have allowed at least some of the genes that contribute to (1,3;1,4)-beta-D-glucan synthesis in the Poaceae to be identified. Whether similar genes and enzymes also mediate (1,3;1,4)-beta-D-glucan biosynthesis in lower plants and fungi is not yet known. Here, we compare the different fine structures of (1,3;1,4)-beta-D-glucans across the plant kingdom, present current information on the genes that have been implicated recently in their biosynthesis, and consider aspects of the cell biology of (1,3;1,4)-beta-D-glucan biosynthesis in the Poaceae. [Full Text]

  • Doblin, MS; Pettolino, FA; Wilson, SM; Campbell, R; Burton, RA; Fincher, GB; Newbigin, E; Bacic, A (2009) A barley cellulose synthase-like CSLH gene mediates (1,3;1,4)-β-d-glucan synthesis in transgenic Arabidopsis. PNAS, 106 (14): 5996-6001

The walls of grasses and related members of the Poales are characterized by the presence of the polysaccharide (1,3, 1,4)-beta-D-glucan (beta-glucan). To date, only members of the grass-specific cellulose synthase-like F (CSLF) gene family have been implicated in its synthesis. Assuming that other grass-specific CSL genes also might encode synthases for this polysaccharide, we cloned HvCSLH1, a CSLH gene from barley (Hordeum vulgare L.), and expressed an epitope-tagged version of the cDNA in Arabidopsis, a species with no CSLH genes and no beta-glucan in its walls. Transgenic Arabidopsis lines that had detectable amounts of the epitope-tagged HvCSLH1 protein accumulated beta-glucan in their walls. The presence of beta-glucan was confirmed by immunoelectron microscopy (immuno-EM) of sectioned tissues and chemical analysis of wall extracts. In the chemical analysis, characteristic tri- and tetra-saccharides were identified by high-performance anion-exchange chromatography and MALDI-TOF MS following their release from transgenic Arabidopsis walls by a specific beta-glucan hydrolase. Immuno-EM also was used to show that the epitope-tagged HvCSLH1 protein was in the endoplasmic reticulum and Golgi-associated vesicles, but not in the plasma membrane. In barley, HvCSLH1 was expressed at very low levels in leaf, floral tissues, and the developing grain. In leaf, expression was highest in xylem and interfascicular fiber cells that have walls with secondary thickenings containing beta-glucan. Thus both the CSLH and CSLF families contribute to beta-glucan synthesis in grasses and probably do so independently of each other, because there is no significant transcriptional correlation between these genes in the barley tissues surveyed. [Full Text]

  • Burton, RA; Wilson, SM; Hrmova, M; Harvey, AJ; Shirley, NJ; Stone, BA; Newbigin, EJ; Bacic, A; Fincher, GB (2006). Cellulose synthase-like CslF genes mediate the synthesis of cell wall (1,3;1,4)-beta-D-glucans. Science, 311 (5769): 1940-1942

A characteristic feature of grasses and commercially important cereals is the presence of (1,3; 1,4)-beta-D-glucans in their cell walls. We have used comparative genomics to link a major quantitative trait locus for (1,3; 1,4)-beta-D-glucan content in barley grain to a cluster of cellulose synthase-like CslF genes in rice. After insertion of rice CslF genes into Arabidopsis, we detected (1,3; 1,4)-beta-D-glucan in walls of transgenic plants using specific monoclonal antibodies and enzymatic analysis. Because wild-type Arabidopsis does not contain CslF genes or have (1,3; 1,4)-beta-D-glucans in its walls, these experiments provide direct, gain-of-function evidence for the participation of rice CslF genes in (1,3; 1,4)-beta-D-glucan biosynthesis. [Full Text]