Engineering synthetic signalling between plants and microbes

植物根系对植物吸收矿物质养分至关重要。此外，它们还与土壤环境和细菌、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，缺乏植物和动物高等细胞中的膜结合结构。然而，尽管细菌可能没有那么复杂的细胞组织，它们却能进行大量植物和动物所没有的化学反应。细菌负责许多营养物质的循环，如N2 （N2也被称为氮气，由两个氮原子由一个强大的三键结合而成），这是一种非常惰性的大气气体。氮气占大气的78%，但非常不活泼，不能直接用作氨基酸、蛋白质和DNA合成所需的氮的来源。然而，少数细菌可以将N2还原（加入氢）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合成为氨基酸和所有其他构成生命的物质。在世界上许多地方，限制植物生长的是以氨或硝酸盐形式存在的氮的供应，而植物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科植物的植物提供的。豆科植物在根上形成根瘤，根瘤菌可以将N2还原为氨，并将其提供给植物，作为碳和能量的来源。这种豆科植物-根瘤菌共生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，尽管豆科植物很重要，但最近它们的使用减少了，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，因为大量的氮被污染到环境中，导致藻类大量繁殖，产生温室气体。豆类使用量下降的部分原因还在于，小麦、玉米、水稻和大麦等谷物的粮食产量比豆类高得多，而且现代农业实践已经优化了豆类的生长。因此，我们正在开发利用将N2还原为氨的细菌（也称为固氮细菌）接种谷物根的方法，使植物无需外部施肥即可获得氨。为了控制这个过程，我们培育了一种植物，它能产生一种叫做根茎碱的信号，根部的细菌可以检测到这种信号。我们现在正在开发控制系统来微调这个过程，这样根瘤素就可以控制细菌合成和分泌氨来喂养植物的根。

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.