Heme Biosynthesis in the Bradyrhizobium Japonicum/Soybean Symbiosis

[9722974] O 'Brian Bradyrhizobium japonicum是大豆的细菌内共生体，它将氮固定在称为根瘤的特殊植物器官的细胞内。研究的广泛目标是了解共生发展和功能所需的过程的调节和协调。固氮是能量密集型的，因此植物和细菌血红素谱的变化伴随着根瘤的发生，以适应这种需求。该项目提出了血红素生物合成是一个受调控的相互作用过程，并与细胞分化和功能协调的假设。此外，该系统对于血红素合成和血红素蛋白功能的研究非常出色，并可作为原核生物和真核生物的范例。(-氨基乙酰丙酸（ALA）是第一个普遍承诺血红素前体，并从P.I.工作的实验室研究表明，寄主来源的ALA可以合成日本刺参血红素。该模型需要一种获取外源ALA的机制，并提示在ALA合成之外或之外的步骤调节细菌血红素生物合成。事实上，数据显示日本芽孢杆菌hemB是一个高度调控的基因。一种名为IRR的新蛋白通过抑制血红素b的表达和间接激活铁转运，直接介导铁对血红素合成的控制；研究hemB和IRR的功能及调控。日本芽孢杆菌的ALA摄取系统已被部分表征，并被证明是由转录调节因子Lrp的同源物控制的。最后，最近的研究结果质疑长期持有的观点，即植物结节血红蛋白血红素是由根瘤菌共生体产生的，这个问题将被重新审视。生活在土壤中的某些细菌可以与大豆和其他农业相关植物形成有益的关系。这种关系赋予植物在没有施用氮肥的情况下在土壤中生长的能力，因此具有经济和环境重要性。此外，共生关系已经成为理解其他生物现象的一个很好的模型，这些现象看起来与正在研究的生物现象不同，但实际上在分子水平上非常相似。本研究的重点是了解日本慢生根瘤菌在与大豆相互作用过程中如何改变以适应其在共生中的作用，以及如何控制能量代谢重要化合物血红素的形成。

9722974 O 'Brian Bradyrhizobium japonicum is the bacterial endosymbiont of soybean that fixes nitrogen within cells of a specialized plant organ called a root nodule. The broad objective of the research is to understand the regulation and coordination of processes necessary for symbiotic development and function. Nitrogen fixation is energy-intensive, and thus changes in the plant and bacterial heme profile are concomitant with nodule ontogeny to accommodate this demand. The project addresses the hypothesis that heme biosynthesis is a regulated, interactive process in B. japonicum, and that it is coordinated with cell differentiation and function. In addition, this system is excellent for studies of heme synthesis and heme protein function, and serves as a paradigm for both prokaryotes and eukaryotes. (-aminolevulinic acid (ALA) is the first universal committed heme precursor, and work from the P.I. 's laboratory indicates that B. japonicum heme can be synthesized by host-derived ALA. This model requires a mechanism for acquiring exogenous ALA, and suggests regulation of bacterial heme biosynthesis at steps other than, or in addition to, ALA synthesis. Indeed, data show that B. japonicum hemB is a highly regulated gene. A novel protein called IRR has been identified that mediates iron control of heme synthesis directly by repressing hemB expression and indirectly by activating iron transport; hemB and IRR function and regulation will be studied. The ALA uptake system of B. japonicum has been partially characterized, and shown to be controlled by a homolog of the transcriptional regulator Lrp. Finally, recent findings question the long-held view that plant nodule hemoglobin heme is derived by the rhizobial symbiont, and that problem will be revisited. Certain bacteria that live in the soil can form a beneficial relationship with soybeans and other related plants of agricultural interest. The relationship confers on the plant the ability to grow in soil in the absence of applied nitrogen fe rtilizer, thus it has economic and environmental importance. In addition, the symbiosis has become a good model for understanding other biological phenomena that appear to differ from the one under study, but in fact are very similar at the molecular level. The research focuses on understanding how the bacterium Bradyrhizobium japonicum changes during its interaction with soybean to adapt to its role in symbiosis, and how formation of heme, a compound important in energy metabolism, is controlled.