Role of the SYM pathway in selecting the root microbiota

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。根周围被这些生物占据的区域被称为根际，这些生物的总称是根际微生物群。微生物也存在于植物的根内，通常在植物细胞之间，被称为内生菌。根际微生物群和内圈微生物群共同构成植物的根微生物群。在过去的几年里已经证明，根部微生物群对植物的健康和生长至关重要，许多微生物被证明是促进植物生长的。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，但它们可以进行植物和动物所没有的大量化学反应。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。然而，最近豆科植物的使用减少了，氮主要通过化学合成肥料提供给作物。生物圈中另一种限制性营养物质是磷酸盐，磷酸盐通常由一组被称为丛枝菌根（AM真菌）的真菌自然提供给植物。氮和磷酸盐对植物生长和作物产量至关重要，因此它们经常被大量添加到农业土壤中。这导致了这些营养物质对地下水的广泛污染，导致这些营养物质流入水道和海洋，导致富营养化，特别是促进了藻类的生长。值得注意的是，AM真菌和根瘤菌都通过一种被称为共同共生途径（SYM）的共同信号网络与植物相互作用。在这项工作中，我们正在研究SYM途径如何控制豆类和谷物的微生物群。我们的目标是了解这些途径如何控制微生物群的不同成员。此外，我们将超越微生物群组成的简单表征，以检查控制机制。这项研究将导致包括豌豆和水稻在内的农业关键作物的植物微生物群特征的一个步骤变化。我们不仅将描述存在的微生物，而且还将培养和描述微生物群关键成员的功能。这项工作超越了微生物存在的简单表征，以识别功能群落成员。

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. The area directly around roots that is occupied by these organisms is known as the rhizosphere and the collective name for the organisms is the rhizosphere microbiota. Microorganisms also reside inside plant roots, usually between plant cells and are knows as endophytes. Together the rhizosphere and endosphere microbiotas makes up the root microbiota of a plant. It has been shown over the last few years that the root microbiota is critical for the health and growth of plants, with many microorganisms shown to be plant growth promoting. 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. However, more recently legume use has declined and nitrogen is mainly provided to crops by chemically synthesised fertiliser. One of the other limiting nutrients in the biosphere is phosphate, which is often naturally provided to the plant by a group of fungi known as the arbuscular mycorrhizae (AM fungi). Nitrogen and phosphate are so crucial to plant growth and crop yield that they are often both added in very large amounts to agricultural soils. This has led to widespread pollution of ground water with these nutrients, leading to run off into water ways and oceans that causes eutrophication where the growth in particular of algae is promoted. Remarkably it turns out that both AM fungi and rhizobia interact with plants using a common signalling network known as the common symbiosis pathway (SYM). In this work, we are investigating how the SYM pathway controls the microbiota of legumes and cereals. Our aim is to understand how the pathways control different members of the microbiota. In addition, we will move beyond simple characterisation of the components of the microbiota to examine the mechanism of control. This research will lead to a step change in characterisation of the plant microbiota of agriculturally critical crops, including pea and rice. Not only will we characterise which microorganisms are present but we will also culture and characterize the function of key members of the microbiota. This work moves beyond simple characterisation of which microorganisms are present to identification of functional community members.