Engineering synthetic signalling between plants and microbes

植物根系对于植物吸收矿质营养至关重要。此外，它们与土壤环境以及细菌、真菌、单细胞动物细胞、线虫和其他生物的复杂组合相互作用。细菌是简单的单细胞微生物，缺乏在植物和动物的高等细胞中发现的膜结合结构。然而，虽然细菌的细胞组织可能不那么复杂，但它们可以进行植物和动物中没有的大量化学反应。细菌负责许多营养物质的循环，例如N2（N2也被称为氮气，由两个氮原子通过强三键结合组成），这是一种非常惰性的大气气体。N2占大气的78%，但非常不活泼，不能直接用作氨基酸，蛋白质和DNA合成所需的氮源。然而，少数细菌可以将N2还原（添加氢）并将其转化为氨（NH3），氨很容易被包括细菌和植物在内的各种生物体纳入氨基酸，然后是所有其他生命的组成部分。在世界许多地区，植物生长的限制是氨或硝酸盐形式的氮供应，而植物生长反过来又支持动物的生命。在过去，大部分氮是由生物固氮提供的，特别是由一组被称为豆类的植物提供的。豆科植物在其根部形成根瘤，其中含有称为根瘤菌的细菌，这些细菌将N2还原为氨并将其供应给植物，以换取碳和能源。这种豆科植物-根瘤菌共生体负责提供生物圈中高达50-60%的生物可利用氮（即氨），因此对地球上的生命至关重要。然而，尽管豆类的重要性，最近它们的使用已经下降，氮主要通过化学合成肥料提供给作物。这对环境产生了重大的负面影响，因为这些氮中的大部分作为污染物损失到环境中，导致藻类大量繁殖并产生温室气体。豆类使用量下降的部分原因也是因为小麦、玉米、水稻和大麦等谷物的产量比豆类高得多，现代农业实践已经优化了它们的生长。因此，我们正在开发使用将N2还原为氨的细菌（也称为固氮细菌）来保护谷物根部的方法，使植物能够在不施用外部肥料的情况下获得氨。为了控制这一过程，我们开发了一种植物，它能产生一种信号，叫做根碱，它们根部的细菌可以检测到。我们现在正在开发控制系统来微调这一过程，以便Rhizopine能够控制细菌合成和分泌氨来喂养植物的根部。

Plant roots are critical for the uptake of mineral nutrients by plants. In addition, they interact with the soil environment and a complex assemblage of bacteria, fungi, single celled animal cells, nematodes and other organisms. Bacteria are simple single celled microorganisms that lack the membrane bound structures found in higher cells of plants and animals. However, while bacteria may have a less complex cellular organisation, they carry out a huge range of chemical reactions not found in plants and animals. Bacteria are responsible for the cycling of many nutrients such as N2 (N2 is also known as nitrogen gas and consists of two nitrogen atoms bound by a strong triple bond), which is a very inert atmospheric gas. N2 makes up 78% of the atmosphere but is very unreactive and cannot be used directly as a source of nitrogen, which is needed for amino acid, protein and DNA synthesis. However, a small number of bacteria can reduce (add hydrogen) to N2 and convert it into ammonia (NH3), which is readily incorporated into amino acids and then all the other building blocks of life, by a wide range of organisms including bacteria and plants. In many parts of the world the limitation to growth of plants, which in turn support animal life, is the supply of nitrogen as ammonia or nitrate. In the past, much of the nitrogen was provided by biological nitrogen fixation, particularly by a group of plants known as legumes. The legumes form nodules on their roots which house bacteria, called rhizobia, which reduce N2 to ammonia and supply it to plants in return for a carbon and energy source. This legume-rhizobia symbiosis is responsible for providing up to 50-60% of the biosphere's biologically available nitrogen (i.e. ammonia) and is therefore essential to life on earth. However, in spite of the importance of legumes more recently their use has declined and nitrogen is mainly provided to crops by chemically synthesised fertiliser. This has major negative impacts on the environment as much of this nitrogen is lost to the environment as pollution causing algal blooms and contributing to greenhouse gases. Part of the decline in legume use is also because cereals such as wheat, maize, rice and barley have much higher grain yields than legumes and modern agricultural practise has been optimised for their growth. We are therefore developing ways to use bacteria that reduce N2 to ammonia (also called nitrogen-fixing bacteria) to inoculate cereal roots to enable the plants to obtain ammonia without external fertiliser application. To control this process, we have developed plants that produce a signal, called rhizopine, that the bacteria on their roots can detect. We are now developing the control systems to fine tune this process so that rhizopine is able to control the synthesis and secretion of the ammonia by the bacteria to feed the roots of plants.