The Evolution of Alleles Conferring Symbiotic Specialization in Legumes

9707697帕克豆科植物与在其根部形成根瘤的细菌(根瘤菌)之间的共生在为自然生态系统和农业提供关键养分(氮)方面具有全球重要性。然而，豆科植物-根瘤菌相互作用的生态学和进化仍然知之甚少。特别是，豆类植物通常被发现在与不同细菌基因型相互作用的能力方面存在遗传差异。影响这种互惠共生的植物基因通常会导致共生专化的差异：一些植物只能与有限数量的根瘤菌菌株成功地相互作用，而另一些植物则与广泛的细菌伙伴成功共生。由于根瘤菌通过提供一种重要的营养物质使植物受益，共生能力有限的植物应该处于不利地位。然而，导致共生专门化的基因在豆科植物种群中普遍存在，这表明还有其他进化过程来补偿任何针对它们的自然选择。这种过程的性质目前尚不清楚，因此这项研究的主要目标是通过实验测试一系列假设，即为什么共生专门化在豆科植物的自然种群中进化得如此普遍。这项研究的主要意义在于，它将揭示豆科植物对细菌共生体的专化或混杂所带来的适应性收益和成本。影响根瘤菌专一性的基因也对提高具有农业意义的豆科植物(如大豆、豌豆、豆类、紫花苜蓿等)的生产力感兴趣。因此，该项目的结果也应该为更好地理解农业生态系统中豆科植物-根瘤菌的相互作用提供一个重要的比较视角。

9707697 Parker The symbiosis between legume plants and bacteria that form nodules on their roots (rhizobia) is globally important in providing a key nutrient (nitrogen) for both natural ecosystems and agriculture. However, the ecology and evolution of legume-rhizobial interactions remain very poorly understood. In particular, legumes are commonly found to be genetically variable in their capacity to interact with different bacterial genotypes. The plant genes affecting this mutualism typically cause differences in symbiotic specialization: some plants can only interact successfully with a limited number of rhizobial strains, while other plants achieve successful symbiosis with a wide range of bacterial partners. Because rhizobia benefit plants by providing an important nutrient, plants with restricted symbiotic abilities should be at a disadvantage. Nevertheless, genes that cause symbiotic specialization are widely prevalent in legume populations, suggesting that there are other evolutionary processes that compensate for any natural selection against them. The nature of such processes is currently unknown, so the primary objective of this research is to experimentally test a series of hypotheses about why symbiotic specialization has evolved to be common in natural populations of legumes. The main significance of this research is that it will reveal the fitness benefits and costs for legume plants associated with being specialized or promiscuous toward bacterial symbionts. Genes that affect rhizobial specificity are also of interest in efforts to improve the productivity of agriculturally-significant legumes (such as soybeans, peas, beans, alfalfa, etc.). Thus, the results of this project should also provide an important comparative perspective for an improved understanding of legume-rhizobial interactions in agroecosystems as well.