Plasmid Biology of Rhizobium leguminosarum

根瘤菌是以其在豆科植物如豌豆、菜豆、扁豆和苜蓿的根部形成固氮根瘤的能力而闻名的细菌。 它们能够使这些植物在不添加合成含氮肥料的情况下生长，其生产和应用在化石燃料消耗和温室气体排放方面具有很高的成本，这使得它们在可持续农业中非常重要。 生产更有效和更有竞争力的根瘤菌菌株用作豆类接种剂是生物技术的主要目标。 然而，引入的根瘤菌菌株的相互作用，并在环境中的菌株之间的遗传转移的潜力，没有得到很好的理解。 根瘤菌在细菌中相对不寻常，因为它们具有大而复杂的基因组，通常由一条染色体和几个非常大的染色体外遗传元件（称为质粒）组成。 质粒往往非常稳定，其中一些质粒的性质介于质粒和染色体之间。 该建议将集中在豌豆根瘤菌生物变种viciae菌株VF 39的质粒上，VF 39是豌豆、小扁豆、蚕豆、野豌豆和各种山豌豆属物种的共生体。重点将放在基因，决定细菌菌株之间的接合转移的机制和后果，以及质粒编码的基因在细菌的生存能力和茁壮成长的土壤，根际和结核环境中的其他作用。这项研究建立在实验室研究大质粒的先前专业知识的基础上，以及细菌和感染它的多种噬菌体的基因组序列的可用性。主要主题将是1）详细分析质粒pRleVF 39 b和pRleVF 39 a上编码的新型质粒转移和IV型分泌系统; 2）鉴定调节质粒转移基因的因子; 3）鉴定蛋白质-与质粒转移有关的蛋白质相互作用4）继续探索质粒编码的分解代谢基因在根瘤菌生态成功中的作用，和5）鉴定与限制噬菌体感染有关的质粒编码的基因座。根瘤菌水平基因转移的信息是至关重要的了解未来的优化菌株（包括遗传增强菌株）作为豆科接种剂释放的后果。 了解属性，包括噬菌体抗性和分解代谢能力，使个别菌株坚持在土壤中，成功地殖民根区，并与其他菌株竞争，是非常重要的选择和设计更好的接种菌株。

Rhizobia are bacteria that are notable for their ability to form nitrogen-fixing nodules on the roots of legume plants, such as peas, beans, lentils and alfalfa. Their ability to allow these plants to grow without addition of synthetic nitrogen-containing fertilizers, whose production and application has a high cost in fossil fuel consumption and greenhouse gas emissions, makes them extremely important in sustainable agriculture. Production of more efficient and more competitive rhizobial strains for use as legume inoculants is a major goal in biotechnology. However, the interactions of introduced rhizobial strains, and the potential for genetic transfer between strains in the environment, are not well understood. Rhizobia are relatively unusual among bacteria in that they have large and complex genomes that usually consist of one chromosome and several very large extrachromosomal genetic elements known as plasmids. The plasmids tend to be very stable, and some of them exhibit properties intermediate between those expected of a plasmid and those of a chromosome. This proposal will focus on the plasmids of Rhizobium leguminosarum biovar viciae strain VF39, a symbiont of peas, lentils, faba beans, vetches, and various Lathyrus species. The emphasis will be on the genes that determine the mechanisms and consequences of transfer by conjugation between bacterial strains, and other roles of plasmid-encoded genes in the ability of the bacterium to survive and thrive in the soil, rhizosphere, and nodule environments. The research builds on previous expertise in the lab studying large plasmids, and the availability of genome sequences of the bacterium and multiple bacteriophages that infect it. The main themes will be 1) detailed analysis of the novel plasmid transfer and type IV secretion systems encoded on plasmids pRleVF39b and pRleVF39a and 2) identification of factors regulating plasmid transfer genes 3) identification of the protein-protein interactions involved in plasmid transfer 4) continued exploration of the role of plasmid-encoded catabolic genes in the ecological success of rhizobia, and 5) identification of plasmid-encoded loci that are involved in limiting phage infections. Information on horizontal gene transfer in rhizobia is vital to understanding the consequences of release of any future optimized strains (included genetically enhanced strains) as legume inoculants. Understanding the attributes, including phage resistance and catabolic capacity, that allow individual strains to persist in soil, successfully colonize the root region, and compete with other strains, is of great importance in selecting and designing better inoculant strains.