Factors controlling N2-fixing ability and competitiveness of rhizobia to nodulate legumes

根瘤菌固氮能力及豆科植物结瘤竞争力的控制因素

• 批准号: BB/W006219/1
• 负责人: Philip Poole
• 金额: $ 99.97万
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FW006219%2F1
• 关键词: Factors; controlling; N2; fixing; ability

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. Rhizobia have been studied for more than 100 years because of this ability to increase yields of legumes crops and rhizobia are routinely applied as inoculants as an alternative to economically expensive chemical fertilizers. The bioavailable nitrogen that is generated in nodules of legumes benefits nonlegume crops grown in rotation or at the same time. However, rhizobial inoculants that have high rates of N2-fixation (i.e. effective strains) when inoculated onto legumes under laboratory conditions often fail to compete in soil for colonisation of legumes against native rhizobia with inferior N2 fixing abilities. This is known as the "rhizobial competition problem". The holy grail of inoculant selection has therefore been to identify elite strains that are both highly effective and competitive. This competition-effectivity problem is of enormous practical importance to use of legumes, but it also highlights the fundamental biological question of what determines the competitiveness of bacteria for colonisation of plant roots. Understanding rhizobial competitiveness is a therefore a prime example of a question that is of both fundamental and applied importance. For the first time in rhizobial research, we are able to assess the bacterial genetic potential and factors rhizobia need for their competitiveness and N2-fixation efficiency in real soil. Research has been conducted under sterile conditions and/or focusing solely on the nodules. Here we propose to step-by-step fully assess the rhizobial life cycle. Our findings will explain why efficient N2 fixers are not necessarily good colonisers. Identifying the essential genes and regulatory pathways will give us detailed knowledge about strain behaviour in different soils and symbiotic success with different plant varieties, allowing us to better select the best inoculants.

植物根对于植物摄入矿物质营养至关重要。此外，它们与土壤环境相互作用，并复杂的细菌，真菌，单细胞动物细胞，线虫和其他生物的复杂组合。细菌是简单的单细胞微生物，缺乏在动植物的较高细胞中发现的膜结构。但是，尽管细菌可能具有不太复杂的细胞组织，但它们在动植物中进行了大量的化学反应。细菌是导致许多营养素（N2）（N2也称为氮气）循环的原因，它是由两个由强三键结合的氮原子组成的），这是一种非常惰性的大气气体。 N2占大气的78％，但没有反应性，不能直接用作氨基酸，蛋白质和DNA合成所需的氮来源。但是，少数细菌可以将氢化（NH3）降低（添加氢），并通过包括细菌和植物在内的广泛的生物体，很容易地掺入氨基酸，然后将其纳入氨基酸，然后将其纳入氨基酸。在世界许多地方，植物生长的局限性又支持动物的生命，是氮作为氨或硝酸盐的供应。过去，许多氮是由生物氮固定提供的，特别是由一组称为豆类的植物。豆科植物在其根部形成结节，这些结节容纳了称为根瘤菌的细菌，可将N2降低至氨，并将其供应植物，以换取碳和能源。这种豆科植物共生的豆科症负责提供生物圈可获得的氮（即氨）的50-60％，因此对地球生命至关重要。然而，尽管豆类的重要性最近很重要，但它们的使用下降了，氮主要通过化学合成的肥料提供给农作物。这对环境产生了重大的负面影响，因为这种氮损失了，因为污染导致藻华和导致温室气体。由于这种能力增加豆类作物和根瘤菌的产量，因此已经研究了根瘤菌已有100多年的历史。在豆类结节中产生的可生物利用氮有益于旋转或同时生长的非乳状作物。但是，在实验室条件下接种到豆类上时，具有高率的N2固定速率（即有效菌株）的根瘤菌接种剂通常无法在土壤中竞争，以实现豆类针对具有较低N2固定能力的天然根瘤菌的定量。这被称为“根茎竞争问题”。因此，接种剂选择的圣杯是确定既高效又有竞争力的精英菌株。这种竞争效应问题对于使用豆类具有巨大的实际意义，但它也突出了基本的生物学问题，即是什么决定了细菌在植物根部定植的竞争力。因此，理解根茎竞争力是一个既重要又应用重要性的问题的主要例子。在根茎研究中，我们第一次能够评估细菌遗传潜力和根茎在实际土壤中其竞争力和N2固定效率的需求。研究是在无菌条件下和/或仅关注结节的。在这里，我们建议逐步充分评估根茎生命周期。我们的发现将解释为什么有效的N2固定器不一定是好的殖民者。识别基本基因和调节途径将为我们提供有关不同土壤中应变行为的详细知识以及不同植物品种的共生成功，从而使我们能够更好地选择最佳的接种剂。