Each year more than 100 billion tons of carbon dioxide are fixed via photosynthesis into plant biomass, a renewable resource for production of chemicals, fuels, clothing, wood products, nanocomposites, food, fiber, gelling/stabilizing agents and nutraceuticals/pharmaceuticals. Plant cell walls are the bulk of plant biomass. Hundreds of millions of years of biotic and abiotic challenge have led plants to evolve complex cell walls that provide longevity spanning thousands of years and mechanical strength supporting 90 meter-tall trees. These striking mechanical and physical properties arise from the fine structure of individual wall polymers, the covalent and non-covalent interactions between them, and their architectural arrangement in each cell type. Among the three cell wall polysaccharides, cellulose, hemicellulose and pectin, pectin is the most complex. A detailed understanding of the structure of plant cell walls across species and cell types is essential for effective and innovative development of plant biomass in a bio-based economy. The pectic polysaccharides, homogalacturonan (HG), rhamnogalacturonan I (RG-I) and rhamnogalacturonan II (RG-II), are defined as a family of glycans containing galacturonic acid linked at the 1- and 4- positions. Among these glycans, HG is the most abundant. HG is a partially methyl-esterified and acetylated homopolymer of alpha-1,4-linked D-galacturonic acid synthesized by the GAUT gene family of proven and putative HG:alpha-1,4-galacturonosyltransferases (HG:GalATs). In efforts to generate plant biomass with reduced recalcitrance for biofuel production, we discovered that modification of <i>GAUT</i> gene expression in woody and grass feedstock leads to reduced biomass recalcitrance and enhanced biofuel production by microbes, and improves plant agronomic performance. The results of studies aimed at identifying the specific wall polymer(s) affected in different <i>GAUT</i> transgenics/mutants, and studies to understand the mechanism(s) for improved wall recalcitrance and agronomic properties, lead us to propose that specific GAUTs synthesize specific HG glycans that are incorporated into unique polysaccharides and proteoglycans with unique roles in the wall. An in depth understanding of the specific polymeric structures, their mechanisms of synthesis, and their chemical, biophysical and biological properties are critical to enable effective use of plant biomass for energy, bioproduct and food production in a sustainable bioeconomy.

Pectins - are they polysaccharides, proteoglycans, glycan domains of multi-glycan polymers, or all three? Evidence from studies of pectic homogalacturonan biosynthetic galacturonosyltransferases and mutants/transgenics thereof

255th National Meeting (2018)

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