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: 9204778
• 负责人: Mark O'Brian
• 金额: $ 17万
• 依托单位: SUNY at Buffalo
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-08-01 至 1995-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9204778&HistoricalAwards=false
• 关键词: Heme; Biosynthesis; Bradyrhizobium; japonicum; Soybean

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 the proposed 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. Some data support the hypothesis that the heme prosthetic group of the plant nodule protein leghemoglobin is bacterial in origin, and work from my laboratory indicates that formation of the bacterial heme moeity itself requires the coordinated effort of both symbionts. Three objectives are proposed which address the two aforesaid hypotheses. i) Determine whether the B. japonicum heme synthesis enzyme ferrochelatase is essential for soybean hemoglobin heme formation using a temperature-sensitive mutant. ii) Characterize the B. japonicum uptake mechanism of the heme precursor delta- aminolevulinic acid (ALA), and ascertain its role in nodule heme synthesis. Data indicate that bacterial uptake of plant-derived ALA is a key feature of an inter-organismic heme pathway in nodules. iii) Construct and characterize a B. japonicum mutant in ALA dehydratase, the second step of the heme synthetic pathway, and study the regulation of the ALA dehydratase gene. The mutant will allow us to determine exactly which heme synthesis steps in the inter-organismic pathway must be bacterial.

缓生根瘤菌是大豆（Glycine max）的细菌内共生体，在称为根瘤的特殊植物器官的细胞内起固氮细胞器的作用。这两种共生体之间发生许多相互作用，以产生、发展和维持结核。提出的工作的广泛目标是了解豆科植物如何与其细菌伙伴沟通，以调节共生所必需的代谢过程。特别是，我们正在阐明日本双歧杆菌和大豆之间控制根瘤中血红素合成的相互作用事件。一些数据支持植物结节蛋白豆红蛋白的血红素假体群起源于细菌的假设，我实验室的工作表明，细菌血红素运动本身的形成需要两个共生体的协调努力。提出了三个目标，解决上述两个假设。i)利用温度敏感突变体确定日本芽孢杆菌血红素合成酶铁螯合酶是否对大豆血红素形成至关重要。ii)表征日本血吸虫对血红素前体氨基乙酰丙酸（ALA）的摄取机制，并确定其在结节血红素合成中的作用。数据表明，细菌对植物来源的ALA的吸收是根瘤中生物间血红素途径的一个关键特征。iii)构建并鉴定日本白螺旋藻血红素合成途径第二步ALA脱水酶突变体，研究ALA脱水酶基因的调控。突变体将使我们能够准确地确定生物间途径中哪些血红素合成步骤必须是细菌。