Elucidating genetic and molecular mechanisms underlying symbiotic specificity in the Medicago-Sinorhizobium mutualism

阐明苜蓿-中华根瘤菌互利共生特异性的遗传和分子机制

• 批准号: 1758037
• 负责人: Hongyan Zhu
• 金额: $ 75.07万
• 依托单位: University of Kentucky Research Foundation
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1758037&HistoricalAwards=false
• 关键词: Elucidating; genetic; molecular; mechanisms; underlying

The availability of nitrogen in the soil is a major limiting factor for agricultural production. Although the use of industrial fertilizers has contributed substantially to feeding the world, the production of nitrogen fertilizers requires fossil fuels and excessive fertilizers cause serious environmental pollution. In contrast, plants of the legume family can make their own nitrogen fertilizer by forming symbiosis with nitrogen-fixing soil bacteria, called rhizobia. This symbiosis culminates in the formation of specialized root organs, called nodules, within which the bacteria convert atmospheric nitrogen into ammonia for use by the plant. One important property of the legume-rhizobial symbiosis is its high level of specificity. Such specificity can take place at various stages of the interaction, ranging from initial bacterial infection and nodulation (nodulation specificity) to late nodule development associated with nitrogen fixation efficiency (nitrogen fixation specificity). This project aims to elucidate genetic and molecular mechanisms that regulate symbiotic specificity in the legume-rhizobia interaction. Such knowledge will facilitate development of novel strategies to enhance the benefits of symbiotic nitrogen fixation for sustainable agriculture. This project will contribute to the training of students at graduate, undergraduate and high school levels. The research group will particularly encourage the participation of members of under-represented undergraduates to join the project.Despite recent advances in our understanding of the signaling pathways leading to root nodule development, the molecular mechanisms underlying natural variation in nodulation capacity and nitrogen fixation efficiency are still not well understood. In the Medicago truncatula- Sinorhizobium meliloti interaction, the Zhu laboratory recently cloned two host genes, NFS1 and NFS2 that regulate nitrogen fixation specificity concerning S. meliloti Rm41 and an NS1 locus containing two receptor-like kinases that restricts infection and nodulation by Rm41. The polymorphic NFS genes encode nodule-specific cysteine-rich (NCR) peptides. In contrast to the predominant notion of NCR peptides as effectors of endosymbionts' differentiation to nitrogen-fixing bacteroids, this finding demonstrated that specific NCRs negatively regulate symbiotic persistence. NFS1 and NFS2 provoke bacterial cell death and early nodule senescence in an allele-specific and rhizobial strain-specific manner, and their function is dependent on the host's genetic background. This project addresses how NCR peptides, on one hand, can induce terminal bacteroid differentiation needed for nitrogen fixation, and on the other hand, some NCR variants result in lysis of bacteroids. Specifically, the project will determine whether the pro- and anti-symbiotic peptides interact with the same bacterial targets, how amino-acids of the peptides affect their function, and how the functions of these peptides are affected by the genetic background. The specific objectives of the research include: (1) characterization of the NFS1 and NFS2 genes and their roles in negative regulation of symbiotic development with Rm41; (2) cloning and characterization of a suppressor of NFS1; and (3) characterization of the NS1 locus that restricts nodulation by Rm41.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

土壤中氮的有效性是农业生产的主要限制因素。虽然工业肥料的使用为养活世界做出了巨大贡献，但氮肥的生产需要化石燃料，过量的肥料会造成严重的环境污染。相比之下，豆科植物可以通过与土壤固氮细菌（称为根瘤菌）形成共生关系来制造自己的氮肥。这种共生关系最终形成专门的根器官，称为结节，其中细菌将大气中的氮转化为氨供植物使用。豆类-根瘤菌共生的一个重要特性是其高度特异性。这种特异性可以发生在相互作用的各个阶段，从最初的细菌感染和结瘤（结瘤特异性）到与固氮效率相关的晚期根瘤发育（固氮特异性）。本项目旨在阐明豆科植物-根瘤菌相互作用中调节共生特异性的遗传和分子机制。这些知识将有助于发展新的战略，以提高共生固氮的可持续农业的好处。该项目将有助于培养研究生、本科生和高中生。研究小组将特别鼓励代表性不足的本科生成员参与该项目。尽管我们对导致根瘤发育的信号通路的理解最近取得了进展，但对促进能力和固氮效率的自然变异的分子机制仍然没有很好的了解。在蒺藜苜蓿与苜蓿中华根瘤菌的互作中，朱氏实验室最近克隆了两个调节根瘤菌固氮特异性的宿主基因NFS 1和NFS 2。苜蓿属Rm 41和NS 1基因座，所述NS 1基因座含有两个限制Rm 41的感染和诱导的受体样激酶。多态性NFS基因编码结节特异性富含半胱氨酸（NCR）的肽。与NCR肽作为内共生体分化为固氮类细菌的效应物的主导概念相反，这一发现表明特定NCR负调节共生持久性。NFS 1和NFS 2以等位基因特异性和根瘤菌株特异性的方式引起细菌细胞死亡和早期根瘤衰老，并且它们的功能依赖于宿主的遗传背景。该项目解决了NCR肽如何一方面诱导固氮所需的终末类菌体分化，另一方面，一些NCR变体导致类菌体裂解。 具体来说，该项目将确定亲和抗共生肽是否与相同的细菌靶标相互作用，肽的氨基酸如何影响其功能，以及这些肽的功能如何受到遗传背景的影响。本研究的具体目标包括：（1）NFS 1和NFS 2基因的鉴定及其在与Rm 41共生发育负调控中的作用：（2）NFS 1抑制基因的克隆和鉴定;以及（3）该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的学术价值和更广泛的影响审查标准。