Identifying novel genes to improve lignocellulosic biomass as a feedstock for bioethanol

The dwindling reserves of fossil fuels, coupled with the environmental consequences of burning these fuels, mean that a more sustainable alternative is required. Bioethanol produced from lignocellulosic biomass is an attractive candidate for the replacement of liquid transportation fuels. Lignocellulosic biomass is composed of plant cell walls, which are extremely resistant to digestion. Converting this biomass to fermentable sugars for bioethanol production therefore requires energetic pretreatment and expensive enzyme applications. To make lignocellulosic bioethanol a commercial reality, the conversion efficiency needs to be improved and one approach of doing so is to produce crops that are more susceptible to hydrolysis. To this end, this study used a forward genetic approach with the objective of identifying genes that affect the digestibility of plant biomass. A chemically mutagenised population of the model grass Brachypodium distachyon was screened for improved saccharification with industrial cellulases. This revealed 12 mutant lines with heritable increases in saccharification. Characterisation of these 12 mutants revealed a range of different alterations in cell wall composition. Interestingly, a number of the mutant lines showed no change in lignin content, which is thought to be the major contributor to cell wall recalcitrance. These results show that saccharification can be significantly improved through a number of distinct modifications of the cell wall, giving the potential for combining more than one of these modifications in biofuel crops to obtain even higher ethanol yields. Furthermore, the mutations seem to have little effect on plant growth, development or stem strength, important traits for crop field performance. Candidate causal mutations of three of the high saccharification mutants have been identified and characterisation of the mutated genes has begun. In the long term, this will enable subsequent examination of orthologous genes in the relevant cereal and grass crops used for biofuel production.