Dissecting the diverse development programmes in different tissues during the development of a nitrogen fixing nodule

植物必须从周围环境中获取元素营养氮，其有效性往往是植物生长的主要限制因素。豆类(豌豆和豆类)有一种独特的策略来应对氮素限制。它们与土壤细菌进行共生相互作用，这些细菌能够固定一种植物无法吸收的大气形式的氮，并将其转化为具有生物活性的氨。这种相互作用涉及细菌进入豆科植物的根部，并形成一个“根瘤”，一个容纳细菌的根部突起。细菌进入与导致结节形成的细胞分裂的协调对于确保细菌感染和固氮结节是至关重要的。我们已经发现了在根的最外层，即细菌进入植物的表皮中控制结瘤反应的一些关键基因。我们还发现了调节表皮下几层反应的基因，在结节结构发育的皮质细胞层。有趣的是，这两个反应系统之间似乎存在遗传重叠，这表明基因的功能是由其活跃的细胞类型定义的。在这个提案中，我们将评估根表皮和根皮层中的结瘤信号机制，特别是将重点放在调节基因表达的转录因子的作用上。我们将结合遗传方法和最先进的基因组方法来发展对这一过程的系统水平的理解。特别是，我们将试图确定转录因子在不同组织中的作用，以及这些转录因子能够协调不同组织中不同发育程序的机制。这将使我们能够确定使植物协调发展从而形成固氮根瘤的机制。

Plants must acquire the elemental nutrient nitrogen from their surrounding environment and its availability is often a major limitation to plant growth. Legumes (peas and beans) have a unique strategy to deal with nitrogen limitation. They enter symbiotic interactions with soil bacteria that are able to fix an atmospheric form of nitrogen that plants cannot take up, and convert it into the biologically active form ammonia. This interaction involves the entry of the bacteria into the roots of the legume plant together with development of a 'nodule', a root outgrowth that houses the bacteria. Co-ordination of bacterial entry with cell division that leads to the formation of the nodule is essential to ensure a bacterially infected and nitrogen fixing nodule. We have uncovered some of the key genes that control nodulation responses in the outermost layer of the root, the epidermis, where bacteria enter the plant. We have also identified genes that regulate responses several layers beneath the epidermis, in the cortical cell layer where the nodule structure develops. Intriguingly there appears to be genetic overlap between these two response systems, suggesting that the function of a gene is defined by the cell type where it is active. In this proposal we will assess the mechanisms of nodulation signaling in the root epidermis and the root cortex and in particular will focus on the role of transcription factors that regulate gene expression. We will combine genetic approaches with state of the art genomic approaches to develop a systems level understanding of this process. In particular we will attempt to define the roles of the transcription factors in the different tissues and the mechanisms by which these transcription factors are able to coordinate diverse developmental programmes in different tissues. This will enable us to define the mechanisms that allow coordinated plant development leading to the formation of the nitrogen fixing nodule.