Exploiting plant cell diversity to understand and improve plant cell wall composition

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The contribution of fossil fuels to global warming has made the generation of biofuels with reduced net CO2 emissions an attractive proposition in the fight against climate change. First generation biofuels use either sugar cane or starch from agricultural crops as feedstocks for fuel production. This conversion of 'food into fuel' however, has the potential to cause food prices to rise, as well as having a negative impact on net CO2 emissions. To address such concerns, the use of inedible residues of food crops, such as husks, stems and leaves, or non-food biomass crops are being developed as second generation biofuel feedstocks. The production of second generation biofuels, from plant biomass, requires conversion of cellulose into simple sugars that can then be fermented to form "cellulosic ethanol" or alternative fuels and chemicals. Cellulose is a polymer of glucose, and its remarkable structural properties means it is the world's most abundant biopolymer and is an abundant source of renewable material that can be used as a source of raw material for chemical and fuel production, or for generating novel biomaterials. Most plant material is composed of woody secondary cell walls that present an abundant source of biomass but the composite nature of the woody cell wall and, in particular, the presence of the phenolic polymer lignin is a major barrier to accessing and exploiting the carbohydrates in the wall. There are other cell types that synthesise a secondary cell walls. In particular, the secondary cell walls of the collenchyma are characterised by a cellulose rich wall that lacks lignin. Tomatoes make a particular kind of 'angular' collenchyma, that provides provide strong support for the growing plant and is characterised by localised secondary cell wall deposition only in the corners of the cells. This raises the interesting question of how cell wall composition is regulated and how the deposition is localised. We have developed a means of enriching for collenchyma that is suitable for generating high quality RNA for expression analysis. The aim is to analyse the tissue specific expression data to identify genes both involved in synthesis of the cell wall and the transcriptional regulators that control its expression as well as investigating the role of cytoskeleton in localising secondary cell wall deposition. The project addresses fundamental question related to the differentiation of plant cell walls including identifying the role of the cytoskeleton in localising cell wall deposition and discovering what enzymes synthesise cellulose and other cell wall cell wall polymers in the secondary cell wall. Furthermore, the high cellulose and low lignin content of collenchyma cell walls makes them an ideal next generation of renewable feedstock for the production of biofuels, other chemicals and materials. The project will lay the groundwork for further work to increase secondary cell wall deposition in collenchyma and engineer other cell types to produce collenchyma type cellulose-rich and lignin-free cells, both of which would dramatically increase the quality of the biomass. This project involves exploiting a novel tissue fractionation technique to identify genes involved in the formation of specialised cell walls. In particular, the project will exploit the availability of complete genome sequence information from both models plants, such as Arabidopsis, and crops species, including tomato, and combine this with our increasing ability to use RNAseq to analyse gene expression from small amounts of tissue and improved bioinformatics tools for analysis of such expression data.