Heme Biosynthesis in the Bradyrhizobium japonicum/Soybean Symbiosis

日本慢生根瘤菌/大豆共生中的血红素生物合成

• 批准号: 9404818
• 负责人: Mark O'Brian
• 金额: $ 30万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-08-15 至 1998-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9404818&HistoricalAwards=false
• 关键词: Heme; Biosynthesis; Bradyrhizobium; japonicum; Soybean

9404818 O'Brian Bradyrhizobium japonicum is the bacterial endosymbiont of soybean (Glycine max) that functions as a nitrogen-fixing organelle within cells of a specialized plant organ called a root nodule. Many interactions occur between the two symbionts for the initiation, development and maintenance of nodules. The broad objective of this work is to understand how leguminous plants communicate with their bacterial partners to regulate metabolic processes essential for symbiosis. In particular, we are elucidating the interactive events between B. japonicum and soybean that control heme synthesis in root nodules. The demand for heme increases in both organisms as the respective cell types differentiate in nodules, and the corresponding heme proteins are an essential feature of symbiotic nitrogen fixation. Preliminary work indicates that the plant host is directly involved in bacterial heme synthesis in nodules, and other data have implicated B. japonicum as the source for soybean hemoglobin heme. The two aforesaid hypotheses are being tested by i) Constructing and characterizing B. japonicum mutants defective in uptake of the heme precursor delta-aminolevulinic acid (ALA). It is possible that bacterial heme can be synthesized from soybean-derived ALA in nodules, and the tenability of this mechanism will be tested by the acquisition and characterization of ALA uptake mutants. ii) Bacterial heme synthesis from plant ALA infers that B. japonicum ALA dehydratase is the first essential bacterial enzyme for heme formation in nodules, and analysis of mutants bears out that prediction. Therefore, the regulation of hemB. the gene encoding ALA dehydratase will be examined. iii) Determining whether B. japonicum can provide the heme prosthetic group of soybean leghemoglobin by construction and characterization of a temperature-sensitive ferrochelatase mutant. The mutant will allow normal nodule development at a permissive temperature, but will permit the inactivation of bacterial heme synt hesis in those nodules. %%% This work will increase our understanding of an important step in soybean and other legume growth. ***

9404818 O ′ Brian Bradyrhizobium japonicum是大豆（Glycine max）的细菌内共生体，其在称为根瘤的特化植物器官的细胞内作为固氮细胞器起作用。 两种共生体之间发生许多相互作用，以启动、发展和维持结核。 这项工作的主要目标是了解豆科植物如何与它们的细菌伙伴沟通，以调节共生所必需的代谢过程。 特别地，我们正在阐明B之间的交互事件。大豆和大豆控制根瘤中血红素合成。 两种生物体对血红素的需求随着各自细胞类型在结节中的分化而增加，并且相应的血红素蛋白是共生固氮的基本特征。 初步研究表明，植物宿主直接参与根瘤中细菌血红素的合成，其他数据也暗示了B。大豆血红蛋白血红素的来源。 通过i）构建和表征B来测试上述两个假设。在血红素前体δ-氨基乙酰丙酸（ALA）的摄取中有缺陷的日本根瘤菌突变体。 细菌血红素有可能是由根瘤中的大豆源ALA合成的，这一机制的可持续性将通过ALA摄取突变体的获得和表征来测试。 ii）细菌从植物ALA合成血红素推断出B.日本根瘤菌ALA脱氢酶是根瘤中血红素形成的第一个必需的细菌酶，突变体的分析证实了这一预测。 因此，hemB.将检测编码ALA脱氢酶的基因。 iii）确定B.通过构建和鉴定温度敏感的亚铁螯合酶突变体，可以提供大豆血红蛋白的血红素辅基。 该突变体将允许在允许的温度下正常的结节发育，但将允许在那些结节中的细菌血红素合成失活。 这项工作将增加我们对大豆和其他豆类生长中重要步骤的理解。 ***