Heme Biosynthesis in the Bradyrhizobium japonicum/Soybean Symbiosis

大豆慢生根瘤菌（Bradyrhizobium japonicum）是大豆的细菌内共生体 （Glycine max）作为一种固氮细胞器， 一种叫做根瘤的特殊植物器官的细胞。 许多 在两个共生体之间发生相互作用用于启动， 结核的形成和维持。 的广泛目标 计划中的工作是了解豆科植物是如何交流的 与它们的细菌伴侣一起调节代谢过程 是共生的必要条件 特别是，我们正在阐明 B之间的交互事件。大豆和大豆 根瘤中血红素的合成。 一些数据支持这一假设 植物根瘤蛋白的血红素辅基 豆血红蛋白是由细菌产生的， 表明细菌血红素部分本身的形成 需要两个共生体的协同努力 三 提出了解决上述两个假设的目标。 i）确定B.血红素合成酶 亚铁螯合酶是大豆血红蛋白血红素形成所必需的 使用一种对温度敏感的突变体 ii）表征B。 日本血吸虫对血红素前体δ- 氨基乙酰丙酸（ALA），并确定其在结节血红素中的作用 合成. 数据表明，细菌吸收植物来源的 ALA是一个关键特征的一个器官间血红素途径， 结节 iii）构造和表征B。突变体 ALA脱水酶，血红素合成途径的第二步，以及 研究ALA脱氢酶基因的调控。 变种人会 使我们能够准确地确定血红素的合成步骤， 器官间途径必须是细菌性的。

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.