Hemicellulose biosynthesis

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.

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Advances in understanding cell wall biosynthesis, including genes responsible for synthesizing the major polymer classes (Bonawitz and Chapple, 2010;Scheller and Ulvskov, 2010;Pauly et al, 2013) and covalent interactions among them (Chiniquy et al, 2012;Bartley et al, 2013;Schultink et al, 2015); regulation of expression of the cell wall biosynthesis genes (Zhao and Dixon, 2011); and metal ion transport proteins that determine the abundance and distribution of plant mineral content (Ma et al, 2006;Yamaji and Ma, 2009;Zhong and Ye, 2015), lay the foundation for genetically engineering bioenergy crop cell wall content and structure. For example, lignin is an important target for genetic engineering for pyrolysis since the major lignin-derived products have a lower O:C ratio, a higher energy value, and are more stable than sugar-derived products (Tanger et al, 2013;Mante et al, 2014).…”

“…GM and GGM have a β-(1-4)-linked backbone with mannose or a combination of glucose and mannose, respectively. Both GM and GGM can be acetylated and substituted by α-(1-6)-linked galactoses (Scheller and Ulvskov, 2010;Rodriguez-Gacio Mdel et al, 2012;Pauly et al, 2013). Relatively depleted in secondary walls, but rich in growing primary walls of dicot species, xyloglucan and pectins are two other polysaccharides in cell walls.…”

CELLULOSE SYNTHASE-LIKE A2, a Glucomannan Synthase, Is Involved in Maintaining Adherent Mucilage Structure in Arabidopsis Seed

“…This result suggested a potential connection between the reduction of Man and the reduction of Glc. In the plant cell walls, Glc monomers link to each other to form cellulose, or link with Xyl/Man to form xyloglucan/glucomannan (Somerville, 2006;Sandhu et al, 2009;Pauly et al, 2013). Because there were no appreciable differences in the GalA, Rha, cellulosic Glc, Ara, or Xyl content in the extracted mucilage between wild-type and csla2-1 seeds (Table II), we hypothesized that the Glc reduction in the csla2-1 mutant might result from the loss of glucomannan in both the nonadherent and the adherent mucilage.…”

The Role of the Plant-Specific ALTERED XYLOGLUCAN9 Protein in Arabidopsis Cell Wall PolysaccharideO-Acetylation

“…Current models of the wall have cellulose microfibrils as the major structural component, with hemicelluloses binding to the microfibrils and pectins as an amorphous matrix in which the cellulose/hemicellulose network is embedded (Pauly et al, 1999a;Somerville et al, 2004;Cosgrove, 2005). Unlike the linear b-1,4-glucan chains making up cellulose microfibrils, hemicelluloses and pectins consist of a diverse set of glycosyl units and linkages as well as other modifications such as methylation and acetylation (Caffall and Mohnen, 2009;Scheller and Ulvskov, 2010;Pauly et al, 2013).…”

“…The hemicellulose xyloglucan (XyG) consists of a b-1,4-glucan backbone with a regular pattern of xylosyl branches, with additional galactosyl, fucosyl, arabinosyl, and/or galacturonosyl substitution depending on the tissue and plant species (Obel et al, 2009;Pauly et al, 2013;Schultink et al, 2014). XyG O-acetylation has been reported on the b-1,4-glucan backbone (Sims et al, 1996;York et al, 1996) as well as on specific galactosyl or arabinosyl side chains (Kiefer et al, 1989;Vierhuis et al, 2001).…”