The first step in engineering nitrogen fixing cereals; transferring the capability to perceive rhizobial bacteria (sLOLA)

发展中国家的小规模农民，特别是撒哈拉以南非洲的小规模农民，既没有购买无机肥料的资源，也没有生产和供应无机肥料的基础设施。再加上这些农民经常在养分严重耗尽的土壤上工作，这意味着产量非常低，很少足以维持他们的需求。找到克服这些养分限制的机制将提高发展中国家农民的产量。即使氮供应量略有增加，每公顷25-50公斤，也能大大提高作物产量，并给小股东农民带来重大经济利益。相比之下，英国农民的每公顷产量是世界上最高的，但维持这些产量需要高投入，特别是氮肥。无机肥料的成本已经占小麦生产成本的近40%，随着能源价格的上涨，这一比例可能会增加。氮肥的施用是英国农业高产的基础，但它们的使用对环境产生了重大的不利影响。寻找维持作物营养的替代手段是可持续和安全粮食生产系统的一个内在组成部分。 豆科植物已经进化出与固氮根瘤菌相互作用的能力，根瘤菌为植物提供氮的需求。在结核内，细菌固氮是通过光合作用提供糖和细菌所需的大量和微量营养素来支持的。在共生状态下，细菌激活固氮并关闭氮同化，使细菌类似于一种新的细胞器，其灵魂目的是为植物提供氮。正是这种整合水平确保了豆科植物-根瘤菌共生体提供大量的固定氮。事实上，多个植物物种已经独立地进化出与固氮细菌相互作用的能力，结果是结节状器官，这为将这种共生能力转移到非豆科植物提供了希望。在本提案中，我们将通过工程化的植物信号，启动将生物固氮转移到谷物的第一步。这是一个复杂的问题。然而，在豆类中获得的知识表明，大部分的机械必要的信号传导是存在于谷物和工程根瘤菌的感知可能比最初预期的更简单。从进化史来看，这一过程的效率和复杂性都在逐步提高。因此，原始的共生体与完全发育的根瘤或复杂的共生结构无关，但一定程度的固氮作用发生了。因此，有可能的是，工程谷物感知固氮细菌可以允许某种程度的植物-细菌联合，可以提供一些固定的氮，而不需要完全分化的根瘤或复杂的感染结构的发展。预计谷物中的固氮工程可能遵循逐渐提高效率和有效性的路径，但是这种工程过程的早期阶段可能提供有用的但不是最大的固定氮水平。

Small-scale farmers in the developing world, particularly those in sub-Saharan Africa, neither have the resources to buy inorganic fertlisers, nor the infrastructure for their production and supply. This coupled with the fact that such farmers are often working with very nutrient deplete soils, means that yields are very low, rarely sufficient to sustain their needs. Finding mechanisms to overcome these nutrient limitations will enhance the yields of developing world farmers. Even slight increases in nitrogen availability, within the range of 25-50 kg per hectare, could significantly improve crop yields and have major economic benefits to small shareholder farmers. In contrast farmers in the UK have some of the highest yields per hectare in the world, but sustaining these yields requires high inputs, in particular nitrogenous fertilisers. The cost of inorganic fertlisers already accounts for nearly 40% of wheat production costs and this is likely to increase as energy prices rise. Application of nitrogen fertilisers underpins the high yields in UK agriculture, but their use comes with significant detrimental impacts on the environment. Finding alternative means to sustain crop nutrition is an intrinsic component of sustainable and secure food production systems. Legumes have evolved the capability to interact with nitrogen-fixing rhizobial bacteria that supply the plant with its nitrogen needs. Within the nodule bacterial nitrogen fixation is supported through the supply of sugars from photosynthesis and a range of macro and micronutrients that the bacteria need. In the symbiotic state the bacteria activates nitrogen-fixation and switches off nitrogen assimilation, making the bacteria analogous to a novel organelle, the soul purpose of which is the supply of nitrogen to the plant. It is this level of integration that ensures that the legume-rhizobial symbiosis delivers a high amount of fixed nitrogen. The fact that multiple plant species have independently evolved the capability to interact with nitrogen fixing bacteria with the result of a nodule-like organ, provides promise for the transfer of this symbiotic capability to non-leguminous plants. In this proposal, we will initiate the first steps towards the transfer of biological nitrogen fixation to cereals, through engineering nodulation signalling. This represents a complex problem. However, the knowledge gained in legumes reveals that much of the machinery necessary for nodulation signalling is present in cereals and engineering the perception of rhizobial bacteria is likely simpler than initially anticipated. The evolutionary history of nodulation appears to have involved a gradual improvement in the efficiency and complexity of this process. Thus primitive symbioses are not associated with fully developed nodules or complex symbiotic structures, yet a degree of nitrogen fixation occurs. It is therefore possible, that engineering cereals to perceive the nitrogen-fixing bacteria may allow some degree of plant-bacterial association that could provide some fixed nitrogen without the need for a fully differentiated nodule or the development of complex infection structures. It is anticipated that the engineering of nitrogen fixation in cereals may follow a gradual path of increasing efficiency and effectiveness, but that the early stages of this engineering process may provide a useful, but not maximal, level of fixed nitrogen.