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营养元素氮，而氮的可用性往往是植物生长的主要限制因素。豆类（豌豆和豆类）有一个独特的策略来处理氮限制。它们与土壤细菌进行共生互动，这些细菌能够固定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。这种相互作用包括细菌进入豆科植物的根部，并形成“结节”，这是一种容纳细菌的根外生长物。细菌进入与细胞分裂的协调导致结核的形成，这对于确保细菌感染和固氮结核是必不可少的。我们已经发现了一些控制根茎最外层结瘤反应的关键基因，也就是细菌进入植物的表皮。我们还发现了调节表皮以下几层反应的基因，在结节结构发育的皮质细胞层中。有趣的是，在这两种反应系统之间似乎存在遗传重叠，这表明基因的功能是由它活跃的细胞类型决定的。在本提案中，我们将评估根表皮和根皮质中结瘤信号的机制，并特别关注调节基因表达的转录因子的作用。我们将结合遗传方法与国家的最先进的基因组方法来开发这个过程的系统级的理解。特别是，我们将尝试定义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导致固氮根瘤形成的协调植物发育的机制。

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.