CAN BACTERIAL PILI AND PLANT HOMOLOGS TO MAMMALIAN PILUS-BINDING PROTEINS BE THE KEY AND LOCK TO SYMBIOTIC NITROGEN FIXATION?-USING NSF-FUNDED GENOME PROJECTS TO FIND NOVEL GENES

该项目的目的是为了更好地了解在与豆科植物发生的固氮共生过程中细菌的附着和感染线的形成。根瘤菌科和豆科植物的细菌之间的固氮共生关系涉及伙伴之间的持续对话，导致细菌附着在植物根部，形成感染线，细菌通过感染线进入根部，以及植物根部结瘤的发育，细菌将大气中的氮转化为易于被植物吸收的氨。淋巴结因子是一种细菌信号分子，对感染丝线的形成和结节的发展至关重要。然而，一些豆科植物与这种模式不同。它们在没有根瘤的情况下与根瘤菌以外的细菌形成固氮缔合。感染丝线的形成和侵袭不需要Nod因子，提示其他细菌因子对感染丝线的形成也很重要，共生关系的建立需要较少的步骤。智力优势：大多数细菌-真核细胞相互作用涉及宿主受体-蛋白质-菌毛相互作用，然后是内吞作用。这种蛋白质-蛋白质相互作用可以介导非结瘤豆科植物的共生。本项目将利用生物化学、遗传学和基因组学方法来评估细菌菌毛的作用，并在结瘤和非结瘤豆科植物共生体中寻找可能的植物菌毛结合蛋白。为了阐明毛在附着和感染线形成中的作用，将在根瘤菌和非根瘤菌物种以及产生的突变体中鉴定参与毛形成的候选基因，以评估共生关系是如何受到影响的。此外，还将在模型豆科植物中鉴定毛丝结合蛋白，并采用基因破坏技术确定其建立关联所需的条件。更广泛的影响：这项研究的结果将为非结瘤豆科植物中固氮共生的早期阶段提供更具体的分析，并将准备在同行评审的期刊上发表，同时也将成为Hirsch博士本科课程“植物与其他生物之间的化学通讯”的讨论主题。一名博士后和一名博士生将直接参与这项研究。此外，一名硕士研究生将协助博士后助理；两人都是亚裔美国女性。

The goal of this project is to better understand attachment and infection thread formation of bacteria during the nitrogen-fixing symbiosis that occurs with legumes. The nitrogen-fixing symbiosis between bacteria of the Rhizobiaceae and legume plants involves a constant dialogue between partners that results in bacterial attachment to plant roots, the formation of infection threads through which the bacteria enter the root, and the development of the nodule on plant roots, in which the bacteria convert atmospheric nitrogen into ammonia that is readily assimilated by the plant. Nod factor, a bacterial signal molecule, is critical for infection thread formation and nodule development. However, some legumes differ from this paradigm. They form nitrogen-fixing associations in the absence of nodules and with bacteria other than rhizobia. Infection thread formation and invasion does not require Nod factor suggesting that other bacterial factors are important for infection thread formation and that fewer steps are required for establishment of the symbiosis. Intellectual Merit: Most bacterial-eukaryotic cell interactions involve host receptor-protein-pili interactions followed by endocytosis. This type of protein-protein interaction could mediate the non-nodulating legume symbiosis. This project will use biochemical, genetic and genomic approaches to assess the role of bacterial pili and to look for putative plant pili-binding proteins in both nodulating and non-nodulating legume symbioses. To elucidate the role of pili in attachment and infection thread formation, candidate genes involved in pili formation will be identified in rhizobial and non-rhizobial species and mutants generated to assess how the symbiosis is affected. Pili-binding proteins also will be identified in model legumes and gene disruption techniques will be employed to determine their requirement for establishment of the association.Broader impacts: The results of this study will provide a more concrete analysis of the earliest stages of the nitrogen-fixing symbiosis in a non-nodulating legume, and will be prepared for publication in peer-reviewed journals as well as being of topic of discussion in Dr. Hirsch's undergraduate course: Chemical Communication between Plants and Other Organisms. A postdoctoral associate will be directly involved in this research as well as a Ph.D. student. In addition, a Masters degree student will be helping the postdoctoral associate; both are female Asian-Americans.