description
- 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.