Understanding and Exploiting Biological Nitrogen Fixation for Improvement of Brazilian Agriculture

除水分外，速效氮是植物生长最受限制的养分。虽然使用化肥可以满足对固定氮的需求，但化肥在农业中的使用已经造成了重大的环境和经济影响。目前，农民使用的氮素只有不到一半被作物吸收。过量的氮泄漏到环境中，导致对土壤和水质量、生物多样性和大气污染的重大影响。然而，一些细菌可以执行一种名为生物固氮的过程，将大气中的氮气转化为氨，氨是一种可以被动植物同化的氮源。这为使用合成肥料提供了一种更可持续的选择。尽管土壤中的固氮菌可以与粮食和能源作物联系在一起，但它们并不容易释放出固定的氮来造福植物，尽管它们可以对植物的生长产生有益的影响。在巴西，由于接种了固氮菌，作物产量显著增加，其中一些固氮菌具有内生生活方式，可以进入植物根和地上部的细胞间隙。这为设计固氮细菌与粮食和能源作物之间更紧密的联系提供了机会，在这种联系中，固定氮被更有效地输送到植物中。这项关于建立虚拟联合中心(VJC)的提议汇集了一组巴西和英国的研究人员，他们致力于了解和利用植物与固氮菌的相互作用，以此作为提高巴西农业生产率的一种手段。利用内生固氮细菌氮素调控的基础知识，我们将对分泌氨以促进作物生长的菌株进行工程改造，并检验这些改良菌株作为接种剂的潜力。我们还将设计选择策略，以分离在根际具有竞争力的联合重氮菌，这些重氮菌与反应良好并在这些内生菌存在时具有生长优势的植物品种有关。我们将确定有效的植物-微生物相互作用所需的基因，并量化与作物产量相关的生物固氮水平。最后，我们将研究使用本地和工程菌株作为接种剂的可能性。为了实现这些目标，我们将利用英国和巴西研究人员在生物固氮、微生物种群动态、细菌和植物遗传学、基因组学和合成生物学方面的强大协同效应和世界领先的专业知识，以设计高效的品种-内生真菌组合，并开发改进的接种技术。加强我们目标作物的固氮承诺为巴西农业带来巨大的好处，同时减少工业氮肥的使用和对环境的影响。

After water, available nitrogen is the most limiting nutrient for plant growth. Although the demand for fixed nitrogen can be met by the use of chemical fertilisers, their use in agriculture has resulted in major environmental and economic impacts. At present less than half of the nitrogen used by farmers is assimilated by crops. Excess nitrogen leaks into the environment, leading to significant effects on soil and water quality, biodiversity, and atmospheric pollution. However, some bacteria can perform a process known as biological nitrogen fixation, which converts nitrogen gas from the atmosphere into ammonia, a source of nitrogen that can be assimilated by animals and plants. This provides a more sustainable alternative to the use of synthetic fertilisers.Although soil-dwelling nitrogen fixing bacteria can associate with food and energy crops, they do not readily release their fixed nitrogen for the benefit of the plant, although they can have beneficial effects on plant growth. In Brazil, significant increases in crop yield have been observed in response to inoculation with nitrogen fixing bacteria, some of which have an endophytic lifestyle and can gain access to intercellular spaces in plant roots and shoots. This provides an opportunity to engineer closer associations between nitrogen-fixing bacteria and food and energy crops, in which fixed nitrogen is delivered more effectively to the plant. This proposal for a Virtual Joint Centre (VJC) brings together a team of Brazilian and UK investigators focused towards understanding and exploiting plant-diazotroph interactions as a means to enhance agricultural productivity in Brazil. Using fundamental knowledge of nitrogen regulation in endophytic nitrogen fixing bacteria, we will engineer strains, which excrete ammonium to benefit crop growth, and examine the potential of these modified strains as inoculants. We will also design selection strategies to isolate associative diazotrophs that are competitive in the rhizosphere in relation to plant varieties that respond well and have a growth advantage in the presence of these endophytes. We will identify genes required for efficient plant-microbe interactions and quantitate the level of biological, nitrogen fixation in relation to crop yield. Finally, we will we examine the potential for the use of native and engineered strains as inoculants. To achieve these objectives, we will exploit strong synergies and world-leading expertise of UK and Brazilian researchers in biological nitrogen fixation, microbial population dynamics, bacterial and plant genetics, genomics and synthetic biology, in order to engineer efficient cultivar-endophyte combinations and develop improved inoculant technologies. Enhancing nitrogen fixation in our target crops promises substantial benefits for Brazilian agriculture, while decreasing the use and environmental impact of industrial nitrogen fertilisers.