Molecular genetics of the Sinorhizobium meliloti- alfalfa symbiosis

meliloti Sinorhizobium meliloti是一种在苜蓿上形成固氮根瘤的细菌。我的研究项目涉及到了解S. meliloti与苜蓿之间的共生关系的各个方面，并扩展到研究S. meliloti作为一种模式土壤微生物。我们研究了根瘤内细菌的碳代谢途径，并在基因组水平上分析了1,683千碱基的pSymB巨型质粒的生物学作用。这项工作使我们参与了S. meliloti的基因组测序，以及最近对其基因组分析的基因组方法的发展。我们最近的NSERC研究重点是分析pSymB稳定复制所需的repABC基因簇，并扩展了我们对S. meliloti中磷酸盐运输的研究，以鉴定许多受PhoB表达调节的基因，以响应磷酸盐（Pi）限制，即phop调节子。在这里，我们建议继续我们对S. meliloti中pi调节代谢的分析：i)通过研究它们的诱导/抑制的生理基础，ii)通过研究这些基因是否在不同的生物（那些基因组测序的生物）中受到pi响应调节。这项工作将导致识别响应pi限制的核心基因集，并通过推断对pi限制的生物学反应。这代表了一种关键细胞成分的基本信息，这种成分在细胞中含量丰富，但往往限制了土壤环境中的生长。我们将研究结核内细菌的碳代谢，并应用复杂的基因组方法来解决哪些基因在植物根系周围的土壤和根际被诱导。这些信息将有助于了解细菌（包括病原体）如何在土壤环境中生存，以及如何改进农业和经济上重要的固氮过程。

Sinorhizobium meliloti is a bacterium that forms N2-fixing root nodules on alfalfa. My research program has dealt with understanding various aspects of the symbiosis between S. meliloti and alfalfa and also extends to studying S. meliloti as a model soil microorganism. We have investigated the pathway of carbon metabolism employed by the bacteria within root nodules and at the genome level, we have analyzed the biological role(s) of the 1,683-kilobase pSymB megaplasmid. That work led to our involvement in the sequencing of the S. meliloti genome and more recently on the development of genomic approaches to the analysis of the it's genome. We focused our recent NSERC research towards the analysis of the repABC gene cluster which is required for stable replication of pSymB and have also extended our work on phosphate transport in S. meliloti towards the identification of many genes whose expression is regulated by PhoB in response to phosphate (Pi) limitation i.e. the Pho-regulon. Here we propose to continue our analysis of Pi-regulated metabolism in S. meliloti: i) by investigating the physiological bases for their induction/repression and ii) by investigating whether these genes are subject to Pi-responsive regulation in diverse organisms (those whose genomes are sequenced). This work will result in the recognition of a core gene set that responds to Pi-limitation and by inference a biological response to Pi-limitation. This represents fundamental information on a key cellular component that is abundant in cells but often limits growth in soil environments. We will investigate carbon metabolism in the bacteria within nodules and also apply sophisticated genomic approaches towards addressing what genes are induced in the soil and rhizosphere surrounding plant roots. This information will help in understanding how bacteria (including pathogens) survive in soil environments and how the agriculturally and economically important nitrogen fixation process can be improved.