Understanding and manipulating lignin biosynthesis in barley

The pathway whereby plants make lignin, a strengthening and waterproofing substance in cell walls, has been extensively studied in dicot plants (tobacco, Arabidopsis and poplar) but little is known about the pathway in grasses. Cell walls and lignin in grasses have several unique features that cannot be understood by studying dicots. We want to study the genes that are involved in making lignin directly in an economically-important grass, barley. We will be able to identify most of the genes quite easily as they are likely to be very similar to the genes already identified in Arabidopsis. However several novel genes may be important in grasses, particularly those involved in generating the features that make grass cell walls unique. We expect that these genes will be switched on at the same time and in the same place as the known lignin genes giving us a handle with which to identify them. For each known or novel gene, we want to determine the function it has in making lignin and whether plants without that gene have any advantages for agriculture or industry. For example, the amount of lignin in a grass influences how difficult it is for animals who are fed that grass to digest it, as lignin itself is fairly indigestible and it surrounds the other, more digestible, components of plant cell walls. Maize plants where specific genes involved in making lignin have been 'knocked-out' or made less efficient through mutation, have reduced amounts of lignin and are more digestible than normal counterparts. We want to see if this is true also in barley by identifying and studying barley mutants in the genes that make lignin. As well as teaching us more about how plant cell walls are made in grasses, this work may lead to new ideas about how to improve the barley crop. In fact, useful mutants identified in the course of this work could be directly incorporated into barley breeding programmes.

The pathway whereby plants make lignin has been extensively studied in dicots but relatively little work has focussed on the pathway in grasses. Cell walls and lignin in grasses have several unique features - such as the incorporation of H-lignin units and ferulates into the wall - that cannot be understood by studying dicots. We want to study the genes that are involved in making lignin directly in barley, a monocot cereal grass with significant economic importance to the UK. We will use a bioinformatics approach to identify barley sequences in EST databases that have homology to Arabidopsis lignin genes. We will identify and sequence cDNA clones for these genes and perform phylogenetic analysis on each gene family in order to better identify the family members most likely to be involved in developmental lignification and to be able to compare the gene family structure with that of Arabidopsis. In addition, we aim to identify novel genes potentially involved in lignification via their co-expression with known lignin genes in microarray analyis of gene expression profiles from a wide range of barley tissues. For each known or novel gene, we want to determine its function on the lignin pathway and whether mutants in that gene have any advantages for agriculture (primarily in digestibility) or industry (for biomass or bioethanol production). The rational behind the applied aspects of this work are that maize mutants in specific lignin genes (brown midrib mutants) have reduced lignin content and improved digestibility. We will identify barley mutants for lignin genes from within a mutant population available at SCRI by TILLING. We will fully characterise the mutants to determine the nature of the lesion and to analyse lignin and potential digestibility changes. Mutants with good agronomic performance but improved digestibility could be rapidly incorporated into barley improvement programmes.