Dissertation Research: The Evolution of the Actinorhizal Symbiosis in Cercocarpus H.B.K. (Rosaceae)

北美西部发现的蔷薇科(蔷薇科)灌木或乔木Cercocarpus属与固氮丝状细菌Frankia之间的互惠共生(光生共生)可能经历了共种。我们建议使用DNA序列和叶绿体限制位点数据来生成Cercocarpus的假想进化史，并使用DNA序列数据来生成Cercocarpus上感染的Frankia菌株的假想进化历史。我们还将测试这些Frankia菌株对Cercocarpus物种和其他有能力与Frankia相互作用的植物的宿主特异性。此外，我们将测试Cercocarpus和Frankia的进化史是否显示出共种模式。Cercocarpus的系统发育将有助于澄清该属令人困惑的分类学、物种边界和物种之间的关系。我们的研究将是对参与放线菌共生的群体中可能的共种的第一次全面检查之一。目前还没有对放线菌属的Frankia感染菌株进行比较广泛的调查，也没有对感染玫瑰家族成员的菌株进行如此广泛的鉴定和描述。有关玫瑰科成员感染Frankia的菌株的信息可用于与其他已知的放线菌群进行比较，我们对Frankia多样性的记录可能会鉴定出可用于农业的菌株。

The mutualism (actinorhizal symbiosis) between the genus Cercocarpus, a shrub or tree in the rose family (Rosaceae) found in western North America, and Frankia, a nitrogen-fixing filamentous bacterium, is a system that may have experienced cospeciation. We propose to generate hypothesized evolutionary histories for Cercocarpus using DNA sequence and chloroplast restriction site data, and strains of Frankia infective on Cercocarpus using DNA sequence data. We will also test the host-specificity of these Frankia strains towards Cercocarpus species and other plants that have the ability to interact with Frankia. In addition, we will test whether the evolutionary histories of Cercocarpus and Frankia exhibit a pattern of cospeciation. The phylogeny produced for Cercocarpus will help clarify the confusing taxonomy, species boundaries, and relationships among species in this genus. Our study will be one of the first comprehensive examinations of possible cospeciation in groups involved in actinorhizal symbiosis. No comparably broad surveys of infective strains of Frankia exist for an actinorhizal genus, nor such broad scale identification and description of strains infective on members of the rose family. Information on the strains of Frankia infective on the members of the rose family can be used in comparisons with other known actinorhizal groups and our documentation of the diversity of Frankia may identify strains that can be used in agriculture.