Molecular genetics of the sinorhizobium meliloti - alfalfa symbiosis

苜蓿中华根瘤菌（Sinorhizobium meliloti）是在苜蓿上形成固氮根瘤的细菌。 我的研究计划涉及理解S. 苜蓿和紫花苜蓿的研究，并扩展到S.苜蓿草木樨作为模式土壤微生物。 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-脱氢酶pSymB巨质粒的生物学作用。 这项工作使我们参与了S.苜蓿基因组和最近的基因组方法的发展，以分析它的基因组。 我们将我们最近的NSERC研究集中在repABC基因簇的分析上，这是pSymB稳定复制所必需的，也扩展了我们在S.苜蓿属植物的许多基因的鉴定，这些基因的表达受PhoB调节以响应磷酸盐（Pi）限制，即Pho调节子。 在这里，我们建议继续我们的分析Pi调节代谢的S。苜蓿草：i）通过研究它们的诱导/抑制的生理学基础和ii）通过研究这些基因是否在不同的生物体（其基因组被测序的生物体）中受到Pi响应性调节。 这项工作将导致识别响应于Pi限制的核心基因组，并推断对Pi限制的生物学响应。 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在土壤和植物根周围的根际中诱导哪些基因。 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，以及如何改善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.