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

高通量测序技术将用于识别影响根瘤菌适应性的突变，这些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。使用实验进化的根瘤菌种群来自模式根瘤菌'苜蓿中华根瘤菌'将能够直接测量的程度，宿主共生体的冲突，询问是否突变，赋予更高的根瘤菌健身主机性能有积极或消极的影响。突变体的鉴定将导致可检验的机制假说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型系统之一。虽然这种相互作用被广泛认为是互利的，但关于根瘤菌在多大程度上可以通过接受植物资源而不提供固定氮作为回报来欺骗宿主植物的争论正在进行中。根瘤菌-豆类共生是可持续农业的一个关键组成部分，因为豆类可以在没有油源肥料的情况下生长，并且在作物轮作中使用时长期增加土壤肥力。豆类包括经济上重要的作物物种大豆、苜蓿、豌豆、菜豆、鹰嘴豆和花生，其为人类和动物营养提供植物基蛋白。因此，在这项研究中所涉及的根瘤菌基因的了解增加，可能会被证明是有用的农业设计更有效的豆类根瘤菌共生。

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.