DISSERTATION RESEARCH: The Genomic Basis of Adaptation in Experimentally Evolved Rhizobia

高通量测序技术将用于鉴定影响根瘤菌适应性的突变，根瘤菌是豆科植物的共生伙伴，为根瘤菌适应共生生活方式的方式提供了一个窗口。利用从模型根瘤菌“Sinorhizobium meliloti”衍生的根瘤菌实验进化群体，通过询问赋予更高根瘤菌适应性的突变是否对宿主性能有积极或消极的影响，将能够直接测量宿主-共生体冲突的程度。突变体的鉴定将导致可测试的机制假设和宏观进化预测的发展，将实验室结果与自然种群联系起来。豆科植物和根瘤菌（形成根瘤并固定大气氮的细菌）之间的共生关系是理解共同进化的最佳模式系统之一。虽然人们普遍认为这种相互作用是互利的，但关于根瘤菌在多大程度上可以欺骗宿主植物，通过接收植物资源而不提供固定氮作为回报，目前还存在争议。根瘤菌与豆科植物的共生关系是可持续农业的关键组成部分，因为豆科植物可以在没有油类肥料的情况下生长，在作物轮作中长期使用可以提高土壤肥力。豆类包括经济上重要的作物品种大豆、苜蓿、豌豆、豆类、鹰嘴豆和花生，它们为人类和动物的营养提供植物性蛋白质。因此，增加对本研究中涉及的根瘤菌基因的了解可能对农业设计更有效的豆科植物-根瘤菌共生有用。

High-throughput sequencing technology will be used to identify mutations that influence the fitness of rhizobia that are symbiotic partners of legumes, providing a window into the ways that rhizobia adapt to the symbiotic lifestyle. Use of experimentally evolved populations of rhizobia derived from the model rhizobium 'Sinorhizobium meliloti' will enable direct measurement of the extent of host-symbiont conflict by asking whether mutations that confer higher rhizobia fitness have positive or negative effects on host performance. Identification of mutants will lead to development of testable mechanistic hypotheses and macro-evolutionary predictions, connecting laboratory results to natural populations.The symbiosis between legumes and rhizobia, bacteria that form root nodules and fix atmospheric nitrogen, is among the best model systems for understanding coevolution. While the interaction is widely assumed to be mutually beneficial, there is ongoing debate over the extent to which rhizobia can cheat their host plants by receiving plant resources without providing fixed nitrogen in return. The rhizobia-legume symbiosis is a key component of sustainable agriculture, as legumes can grow without oil-derived fertilizers and enrich soil fertility over the long-term when used in crop rotations. Legumes include the economically important crop species soy, alfalfa, pea, bean, chickpea, and peanut that provide plant-based protein for human and animal nutrition. Thus, increased understanding of the rhizobia genes implicated in this study may prove useful to agriculture for designing more efficient legume-rhizobia symbioses.