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

化石燃料对全球变暖的贡献，使二氧化碳净排放量减少的生物燃料的产生成为应对气候变化的一个有吸引力的命题。第一代生物燃料使用甘蔗或来自农作物的淀粉作为燃料生产的原料。然而，这种“食品转化为燃料”的过程有可能导致食品价格上涨，并对二氧化碳净排放量产生负面影响。为了解决这些关切，正在开发使用不能食用的粮食作物残留物，如壳、茎和叶，或非食用作物生物质作物，作为第二代生物燃料原料。从植物生物质中生产第二代生物燃料需要将纤维素转化为单糖，然后单糖可以发酵形成“纤维素乙醇”或替代燃料和化学品。纤维素是葡萄糖的聚合物，其非凡的结构特性意味着它是世界上最丰富的生物聚合物，也是可再生材料的丰富来源，可用作化学和燃料生产的原材料来源，或用于产生新的生物材料。大多数植物材料由木质次生细胞壁组成，具有丰富的生物量来源，但木质细胞壁的复合性，特别是酚性聚合物木质素的存在，是获取和利用壁中碳水化合物的主要障碍。还有其他类型的细胞可以合成次生细胞壁。具体地说，厚壁组织的次生细胞壁的特征是富含纤维素的壁缺乏木质素。西红柿形成一种特殊的“棱角”厚壁组织，为生长的植物提供强有力的支持，其特点是仅在细胞的角落内有局部的次生细胞壁沉积。这提出了一个有趣的问题，即细胞壁的组成是如何调节的，沉积是如何定位的。我们开发了一种丰富厚壁组织的方法，该方法适合于生成高质量的RNA用于表达分析。其目的是分析组织特异性表达数据，以确定参与细胞壁合成的基因和控制其表达的转录调节因子，并研究细胞骨架在定位次生细胞壁沉积中的作用。该项目解决了与植物细胞壁分化有关的基本问题，包括确定细胞骨架在定位细胞壁沉积中的作用，以及发现在次生细胞壁中是什么酶合成纤维素和其他细胞壁聚合物。此外，厚角组织细胞壁的高纤维素和低木质素含量使其成为生产生物燃料、其他化学品和材料的理想下一代可再生原料。该项目将为进一步增加厚壁组织中的次生细胞壁沉积以及改造其他类型的细胞以生产厚壁组织类型的富含纤维素和不含木质素的细胞奠定基础，这两种细胞都将极大地提高生物质的质量。该项目涉及利用一种新的组织分离技术来识别与形成特殊细胞壁有关的基因。特别是，该项目将利用模式植物(如拟南芥)和作物物种(包括番茄)的完整基因组序列信息，并将其与我们日益增长的使用RNAseq分析少量组织中的基因表达的能力和用于分析此类表达数据的改进的生物信息学工具相结合。

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.