Legume-Rhizobium Interactions that Maintain Mutualism

维持互利共生的豆科植物-根瘤菌相互作用

• 批准号: 0212674
• 负责人: Robert Ford Denison
• 金额: $ 21万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-08-01 至 2004-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0212674&HistoricalAwards=false
• 关键词: Legume; Rhizobium; Interactions; Maintain; Mutualism

The importance of legume plants to nitrogen budgets of many natural and agricultural ecosystems depends largely on their interactions with rhizobia, soil bacteria that can live inside root nodules and convert nitrogen gas into "fixed" nitrogen that their plant host can use. Rhizobia vary in costs and benefits to their hosts. Why do many, but not all, rhizobia use plant photosynthate (carbohydrates) to fix nitrogen that mainly benefits their hosts, rather than hoarding that photosynthate to support their own future survival and reproduction? This is especially puzzling since each plant typically hosts several competing strains of rhizobia. Strains that fix nitrogen may increase host photosynthesis, thereby increasing the pool of available photosynthate, but if all strains share in this collective benefit then selfish strains that hoard photosynthate should displace those that fix more nitrogen. Why hasn't this happened? Preliminary data appear to show that plants can monitor individual root nodules and cut off resources (including oxygen) to those that fix little or no nitrogen. Mathematical models show that such plant "sanctions" would be an effective deterrent to rhizobial "cheating," but additional research is needed on the mechanisms of plant sanctions and on their effects on survival and reproduction of rhizobia. Various experiments will expose some nodules to a nitrogen-free atmosphere, while allowing other nodules on the same plant to fix nitrogen. Noninvasive monitoring of nodule physiology and methods to count rhizobia are working well, and we also plan to measure resource levels in rhizobia. The importance to soil populations of rhizobial release from nodules, relative to increased reproduction of rhizobia already in the soil, will be determined using rhizobia expressing two different fluorescence genes. DNA fingerprinting of rhizobia collected from nodules in the field will test the key hypothesis that mixed nodules (containing two or more strains) are rare. Although details will differ, our research may be relevant to any system in which cooperation can break down, such as expulsion of algae by bleaching corals.

豆类植物对许多天然和农业生态系统的氮预算的重要性在很大程度上取决于它们与根瘤内生存并将氮气转化为植物宿主可以使用的氮气中的氮气中的土壤细菌的相互作用。 根瘤菌的成本和收益各不相同。 为什么许多但不是全部，根瘤菌使用植物光合物（碳水化合物）来修复主要受益于宿主的氮，而不是ho积光合剂来支持他们自己的未来生存和繁殖？ 这尤其令人困惑，因为每种植物通常都有几种相互竞争的根瘤菌菌株。 固定氮的菌株可能会增加宿主的光合作用，从而增加可用光合作用的池，但是如果所有菌株都具有这种集体益处，那么自私的菌株，ho积光合剂应该取代那些固定更多氮的人。 为什么没有发生？ 初步数据似乎表明植物可以监测单个根结节，并切断很少或没有氮的人（包括氧）（包括氧）。 数学模型表明，这种植物的“制裁”将是对根瘤性“作弊”的有效威慑，但是需要对植物制裁机制及其对根茎生存和繁殖的影响进行其他研究。 各种实验将使某些结节暴露于无氮气氛中，同时允许同一植物上的其他结节固定氮。 对结节生理的无创监测和计算根瘤菌的方法的运作良好，我们还计划测量根瘤菌的资源水平。 将使用表达两种不同荧光基因的根瘤菌确定，将对土壤中的根瘤菌的繁殖相对于根瘤菌的繁殖增加，对根瘤菌释放的土壤种群的重要性。 从田间结节收集的根瘤菌的DNA指纹识别将检验的关键假设，即混合结节（包含两个或多个菌株）很少见。 尽管细节会有所不同，但我们的研究可能与任何合作可以分解的系统有关，例如通过漂白珊瑚驱逐藻类。