Cell wall lignin programme: Manipulating lignin to improve biofuel conversion of plant biomass

World demand for energy and fuel continues to increase but current resources of oil and gas are finite. This, and increasing concern about rising CO2 levels and climate change, has generated renewed interest in alternative fuel sources. Plant biomass can be used to produce energy, either directly by burning it or by using it as the raw material from which bacteria and yeasts can produce biofuels. However the process of converting plant materials into biofuel (such as bioethanol) is not yet very efficient and needs to be improved to make it economically viable. One way of improving plant materials for biofuel production would be to manipulate the structure of plant cell walls, since it is resistant polymers in these walls that prevent microbial enzymes from degrading the plant material into simple sugars and ethanol. One of the most important cell wall polymers in this respect is lignin. Fortunately, we know quite a lot about how lignin is made and how it can be manipulated in woody plants. However much of the plant biomass that could be used to produce energy comes from grasses, and more research is therefore needed to enable us to manipulate lignin in these types of plant. Barley is a good model for the grasses that might be grown for energy applications, and there are more research tools available for barley than for most other grasses. Barley and wheat straw waste could also be useful resources for biofuel production, and most genetic discoveries in barley are usually easily transferable to wheat. This project aims to determine how lignin content and structure influence (1) the amount of sugars that can be released from barley straw; (2) how efficiently these sugars can be converted into biofuels; and (3) the amount of energy that can be released from barley straw by combustion. This will indicate how the polymer can best be manipulated to make it easier to produce biofuels from plant biomass. We also aim to determine whether any lignin biosynthesis genes are important for barley disease resistance or stem strength, so that we can determine how to manipulate lignin while keeping plants healthy. The genes and genetic markers that we isolate can be used directly in energy crop improvement breeding programmes. Because we will be looking at a lot of different barley varieties, we will also be able to identify which current varieties are best for biofuel production and for burning for heat and energy.

Plant biomass is made of cell walls of cellulose, hemicellulose, and lignin (lignocellulose). It is difficult release the lignocellulosic sugars for biofuel production because lignin is extremely resistant to degradation. We have already proven that manipulating lignin can make cellulose more accessible for papermaking and forage digestibility. It could just as easily be manipulated to improve saccharification of plant biomass, making biofuels more feasible and competitive. We will study the relationship between lignin content/composition and (1) saccharification/fermentation of straw; (2) combustion of different straws. We will work in barley, a good research model for biomass grasses. We will isolate barley genes, alleles, and genetic markers that associate with high saccharification. These can subsequently be used in MAS of improved energy crops. We will also investigate whether any lignin genes are associated with disease resistance or stem strength so that we know how to manipulate lignin while keeping plants healthy. We will achieve this by performing QTL mapping and novel association genetics using both a 'candidate gene' (lignin genes) and a 'hypothesis-free' genome-wide approach. This will tell us which lignin genes most influence saccharification and whether we can manipulate them without affecting disease resistance and stem strength. It will also point out other major loci affecting saccharification, as will eQTL analysis. If possible, we will identify and clone these genes which could be novel candidates for manipulating lignin to optimize biofuel production. Among the genotypes we investigate, there will be TILLING mutants and transgenics suppressed in lignin gene expression, enabling us to determine the effects of more extreme lignin gene alleles or manipulations. We will also characterize the natural diversity that exists in barley landraces for these genes. Useful mutant and landrace alleles can be directly incorporated into breeding programmes.