RESEARCH-PGR: Leveraging the Medicago HapMap to characterize genome-by-genome interactions in nitrogen-fixing symbiosis

氮是合成氨基酸和蛋白质所必需的，是人类饮食的基本组成部分。氮也是植物所需的最重要的营养素之一，通常在农业系统中作为肥料施用。然而，豆科植物有能力通过形成根瘤与专门的固氮土壤细菌建立共生关系，其中细菌固定大气氮;固定的氮被植物用于蛋白质合成。共生体具有相互识别分子信号的机制，这反过来又启动了导致根瘤形成的过程。 然而，有显着的遗传变异之间的细菌菌株和豆类之间的能力，以相互作用的共生。这项建议的目的是确定细菌和植物基因和基因变异负责最有效的相互作用。这一目标将通过鉴定细菌菌株来实现，这些菌株在大混合物中在其在蒺藜苜蓿（桶状苜蓿）根部形成根瘤的能力方面胜过其他菌株。这些实验将进行大量收集的桶medic加入代表大部分的物种的变化。因此，这些结果有望鉴定出最具竞争力的菌株和植物种质。最具竞争力的类型的DNA序列的定量分析预计将揭示在共生相互作用中最有效的细菌和植物基因的身份。该项目将培训几名本科生。由豆科植物-根瘤菌共生介导的生物固氮为自然生态系统和农业生态系统提供氮，并导致豆科植物具有富含氮的叶子和种子，使其成为膳食蛋白质的一些最重要的来源。因此，这种共生关系是可持续农业系统的关键组成部分。豆科植物-根瘤菌共生体系是研究细菌和植物基因组间功能协调的理想体系。虽然双方都从这种关系中受益，但并非所有的伙伴关系都同样有益。宿主-根瘤菌相互作用的结果取决于合作伙伴的基因型。这意味着没有一种根瘤菌菌株能为所有植物基因型提供最大的益处，不同的根瘤菌菌株受到不同植物基因型的青睐。这个建议的目的是确定的基因组基础，在互利共生，这可能使操纵的相互作用，以最大限度地提高生物固氮G × G的变化。PI开发了一种选择和重测序测定法，以确定在多样化的多菌株群落中具有最大适应性的菌株。PI建议完善和评价该试验性能的耐用性，以满足各种生物学和统计学挑战。该项目的更广泛影响包括对农业部门和环境的直接好处，这将导致更有效的固氮系统和本科生的培训。

Nitrogen is required for the synthesis of amino acids and proteins, essential components of the human diet. Nitrogen is also one of the most important nutrients required by plants, and it is normally applied as fertilizer in agricultural systems. However, legumes have the ability to establish a symbiotic association with specialized nitrogen-fixing soil bacteria through the formation of root nodules where the bacteria fix atmospheric nitrogen; the fixed nitrogen is used by the plant for protein synthesis. The symbionts have mechanisms that recognize molecular signals from each other, which in turn initiate processes that lead to the formation of root nodules. However, there is significant genetic variation among bacterial strains and among legumes in their abilities to interact symbiotically. The objective of this proposal is to identify bacterial and plant genes and gene variants responsible for the most efficient and effective interactions. This objective will be accomplished by identifying the bacterial strains that outcompete other strains in a large mixture in their ability to form nodules in roots of Medicago truncatula, the barrel medic. These experiments will be carried out with a large collection of barrel medic accessions representing most of the variation in the species. Thus, the results are expected to identify the most competitive strains and plant accessions. Quantitative analysis of the DNA sequences of the most competitive types is expected to reveal the identity of the bacterial and plant genes that are the most effective in the symbiotic interaction. The project will train several undergraduate students. Biological N-fixation mediated by legume-rhizobium symbiosis contributes N to both natural and agro-ecosystems, and results in legumes having N-rich leaves and seeds that make them some of the most important sources of dietary protein. For this reason, this symbiosis is a critical component of sustainable agricultural systems. The legume-rhizobia symbiosis represents an ideal system to study the coordination of function between a bacterial and a plant genome. Although both partners benefit from this relationship, not all partnerships are equally beneficial. The outcome of host-rhizobia interactions depends on the genotypes of the partners. This means that there is not a single rhizobium strain that confers the greatest benefit to all plant genotypes, and that different rhizobia strains are favored by different plant genotypes. The objective of this proposal is to identify the genomic basis that underlies G x G variation in mutualism, which could enable manipulation of the interaction to maximize biological N-fixation. The PIs have developed a select and resequence assay to identify strains with the greatest fitness in a diverse multistrain community. The PIs are proposing to refine and evaluate the robustness of the performance of this assay that will satisfy various biological and statistical challenges. The Broader Impacts of this project include the direct benefits to the agricultural sector and the environment that will result from more efficient nitrogen-fixation systems and the training of undergraduate students.