Plant cell wall biosynthesis: genetic, biochemical and functional genomics approaches to the identification of key genes

Abstract

SummaryCell walls are dynamic structures that represent key determinants of overall plant form, plant growth and development, and the responses of plants to environmental and pathogen-induced stresses. Walls play centrally important roles in the quality and processing of plant-based foods for both human and animal consumption, and in the production of fibres during pulp and paper manufacture. In the future, wall material that constitutes the major proportion of cereal straws and other crop residues will find increasing application as a source of renewable fuel and composite manufacture. Although the chemical structures of most wall constituents have been defined in detail, the enzymes involved in their synthesis and remodelling remain largely undefined, particularly those involved in polysaccharide biosynthesis. There have been real recent advances in our understanding of cellulose biosynthesis in plants, but, with few exceptions, the identities and modes of action of polysaccharide synthases and other glycosyltransferases that mediate the biosynthesis of the major non-cellulosic wall polysaccharides are not known. Nevertheless, emerging functional genomics and molecular genetics technologies are now allowing us to re-examine the central questions related to wall biosynthesis. The availability of the rice, Populus trichocarpa and Arabidopsis genome sequences, a variety of mutant populations, high-density genetic maps for cereals and other industrially important plants, high-throughput genome and transcript analysis systems, extensive publicly available genomics resources and an increasing armoury of analysis systems for the definition of candidate gene function will together allow us to take a systems approach to the description of wall biosynthesis in plants.

The Genetics and Transcriptional Profiles of the Cellulose Synthase-Like HvCslF Gene Family in Barley

“…Thus, mutations in the Arabidopsis KOR gene, which encodes a (1,4)-b-Dglucanase, lead to large reductions in wall cellulose. The possible point of participation of hydrolytic enzymes in cellulose synthesis is unknown, but the hydrolase could be involved in trimming or editing nascent cellulose chains (Szyjanowicz et al, 2004), or possibly in releasing newly synthesized chains from the biosynthetic enzymes (Farrokhi et al, 2006).…”

“…The type II enzymes were initially believed to transfer glycosyl substituents onto a polysaccharide backbone from the sugar nucleotide donor in a single catalytic event (Farrokhi et al, 2006), as exemplified by the a-D-xylosyltransferases that add single a-D-xylosyl residues to the (1,4)-b-D-glucan backbone of wall xyloglucans (Faik et al, 2002). However, it has been shown recently that GAUT1, a type II galacturonyltransferase of the GT8 family, is capable of mediating the synthesis of the homogalacturonan backbone of pectic polysaccharides (Sterling et al, 2006).…”

“…The type I polysaccharide synthase group includes enzymes with an action pattern based upon the iterative transfer of glycosyl residues from sugar nucleotide donors onto main chain backbones of wall polysaccharides (Farrokhi et al, 2006). These are large integral membrane proteins, containing up to 1,000 amino acid residues and up to eight transmembrane helices, and were traditionally believed to catalyze the synthesis of the backbones of wall homopolysaccharides such as cellulose or of wall heteropolysaccharides such as heteroxylans, xyloglucans, or glucomannans (Doblin et al, 2002).…”

Functional Identification of Two Nonredundant Arabidopsis α(1,2)Fucosyltransferases Specific to Arabinogalactan Proteins

“…18). Although progress in elucidating the genes responsible for the biosynthesis of several plant cell wall polysaccharides is being made, virtually nothing is known about the mechanisms and enzymes responsible for the glycosylation of AGPs (19). Although the Golgi complex has been shown to be involved in hydroxyproline-rich glycoprotein glycosylation a while ago (20) and an arabinosyltransferase (AraT) activity for extensin was identified in particulate membranes (21), only recently was an Arabidopsis gene At2g35610 (a member of the GT77 family) for this AraT activity identified (22).…”

A Barley Xyloglucan Xyloglucosyl Transferase Covalently Links Xyloglucan, Cellulosic Substrates, and (1,3;1,4)-β-D-Glucans

“…Xyloglucans and pectic polysaccharides are the major noncellulosic polysaccharides of primary walls from dicotyledonous plants, whereas in the Poales and related commelinoid monocots, including commercially important cereals and grasses, glucuronoarabinoxylans and (1,3;1,4)-␤-D-glucans are the predominant noncellulosic wall polysaccharides, and levels of pectic polysaccharides, glucomannans, and xyloglucans are relatively low (3). In addition, wall composition and the fine structures of component polysaccharides vary depending upon the growth phase, cell type, cell position, and local region within the wall (4,5).…”