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Feature: Plant sugars provide clues to sustainable bioenergy production

Winter 2010

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BBSRC-funded research to manipulate the levels of fermentable sugars contained within plant cell walls could assist in the development of sustainable biofuel production.

The impact of climate change, combined with dwindling fossil fuel reserves and their rising cost, suggest that we need to make greater use of plant-based biomass as a renewable chemical feedstock and as an energy source.

Fermenting plant material is a basis of biofuel production. Understanding how sugars are locked into plant cell walls will enable researchers to select the right plants and the right enzymes to release the maximum amount of sugars for conversion to biofuels.

Plants produce a diverse range of sugars which provide energy stores in seeds and form the backbone of plant cell walls. But these ‘polysaccharides’ are of considerable structural complexity in ways that we are only beginning to understand. Recent efforts to unravel the biosynthetic machinery that constructs individual polysaccharides are beginning to provide fundamental insights into plant development, and could hold the key to optimising fermentation processes.

Unravelling complexity

With the help of the model plant Arabidopsis, a team of BBSRC-funded plant scientists at the University of Cambridge has been able to manipulate the levels of the polysaccharide glucomannan in the plant cell wall. Their findings were published recently in The Plant Journal.

By producing Arabidopsis ‘knock out’ mutants the team showed that three enzymes within the cellulose synthase-like (CSL) family, CSLA2, CSLA3 and CSLA9, are responsible for the production of all detectable glucomannan
in stems.

"This is the first demonstration in plants that the CslA gene subfamily is responsible for glucomannan synthesis," says Dr Paul Dupree. "Importantly, we have shown that the quantity of glucomannan can be increased or decreased in the stem with no visible detrimental effects on plant development or cell wall strength".

In contrast, the team also demonstrated that changing glucomannan levels had a clear effect on seed development.

"Both under- and over-expression of CSLAs during embryogenesis can lead to embryo death," says Dupree.

Being able to increase glucomannan specifically in harvestable plant organs, such as the stem, may be a good target for bioenergy crops where higher proportions of enzyme- accessible fermentable sugars, such as those in glucomannan, would be advantageous.

From small things…

The synthesis of glucomannan is now one of the best understood among plant cell wall polysaccharides. This study clearly demonstrates the versatility of the little weed Arabidopsis as a research tool. Plant scientists around the world continue to gain insights into the genetic, molecular and cellular biology of flowering plants. Not only is this leading to a range of applications in crop breeding, but also in the development of non-food crops for bioenergy production.

Dr Dupree, who leads the Cell Wall Sugars Research Programme within the BBSRC Sustainable Bioenergy Centre (BSBEC), believes that it is important to avoid any negative impacts of the bioenergy industry on food production.

This research was a featured article in the Plant Journal, 2009: 60, 527-538

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