Suppression of rhizobial reproduction by legumes: Implications for mutualism

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。根瘤菌是一种可以生活在土壤中的细菌，也可以共生在大豆或苜蓿等植物的根瘤内。 尽管许多根瘤菌为它们的宿主植物提供氮，为农民节省了数十亿的肥料成本，但在某些地区，效益较低的菌株会造成问题。 一些宿主，包括苜蓿和豌豆，当它们开始提供氮时，会使根瘤菌膨胀。 与大豆或豇豆根瘤中的非膨胀根瘤菌不同，膨胀的根瘤菌显然失去了繁殖能力，但根瘤菌的膨胀是否对植物有益？ 为了找到答案，研究人员将在作物和宿主根瘤菌的野生植物的家谱上绘制这种特征，看看引起肿胀的进化是否不止一次，这表明对植物有积极的好处。 三个双宿主根瘤菌（加上不同的能力，以囤积资源的突变体）将被用来衡量根瘤菌膨胀的成本和效益的植物的影响。 植物对根瘤菌的防御已经在大豆中得到证实，根瘤菌提供很少或没有氮，将在施加细菌肿胀的物种中进行测试。 这项研究将增加对为农业和自然生态系统提供氮的共生的理解，并对其他重要的共生产生影响。 研究结果可以指导作物的发展，选择性地用最好的根瘤菌富集土壤，减少未来的肥料需求。 将为本科生、至少一名研究生和一名博士后研究员提供教育机会。 两名女高中生已经赢得了国际科学博览会的旅行，在首席研究员的实验室进行研究，在那里这种指导将继续是一个优先事项。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Rhizobia are bacteria that can live in soil, but also symbiotically, inside root nodules on plants like soybean or alfalfa. Although many rhizobia provide their host plants with nitrogen, saving farmers billions in fertilizer costs, less beneficial strains cause problems in some areas. Some hosts, including alfalfa and pea, make rhizobia swell up as they start to provide nitrogen. Unlike the nonswollen rhizobia from soybean or cowpea nodules, swollen rhizobia apparently lose the ability to reproduce, but does rhizobial swelling somehow benefit the plant? To find out, the investigators will map this trait on the family tree for crops and wild plants that host rhizobia, to see if causing swelling evolved more than once, suggesting a positive benefit to the plants. Three dual-host rhizobia (plus mutants that differ in their ability to hoard resources) will be used to measure effects of rhizobial swelling on costs and benefits to the plants. Plant defenses against rhizobia that provide little or no nitrogen, already demonstrated in soybean, will be tested in species that impose bacterial swelling. This research will increase understanding of a symbiosis that supplies nitrogen to agricultural and natural ecosystems, with implications for other important symbioses. Results could guide the development of crops that selectively enrich soils with the best rhizobia, decreasing future fertilizer requirements. Educational opportunities will be provided for undergraduates, at least one graduate student, and a postdoctoral researcher. Two female high school students have already won trips to the International Science Fair for research done in the principal investigator's laboratory, where such mentoring will continue to be a priority.