Regulation of Heme Biosynthesis in the Bradyrhizobium japonicum/Soybean Symbiosis

研究大豆固氮根瘤中血红素生物合成的调控是为了了解细菌共生菌日本慢生根瘤菌如何与植物相互作用来调节共生所必需的代谢过程。细菌血红素被认为是植物根瘤蛋白豆状血红蛋白的辅基，因此在豆状血红蛋白的形成过程中，血红素和脱脂蛋白的合成必须通过各自的有机体来协调。实验将阐明日本双胞菌血红素生物合成途径在豆类血红蛋白形成中的确切作用，并确定血红素合成基因在根瘤发育过程中如何调节。具体目标是(I)分离日本双胞菌血红素合成突变体，(Ii)确定细菌血红素合成损伤对豆类血红蛋白合成的影响，(Iii)分离和鉴定日本血球菌血红素合成基因，以及(Iv)研究根瘤相关因子和细菌调节蛋白对血红素合成基因的调控。最后，细菌血红素合成的调节将与豆类血红蛋白的形成相关。生物固氮很重要，因为它是一种廉价且对环境无害的氮肥来源。在分子水平上了解植物与微生物的相互作用，对于任何试图通过基因工程改善共生或将其扩展到其他植物的尝试都是重要的。对慢生型大豆根瘤菌/大豆相互作用的研究将提供更好的理解，并有助于了解血红素生物合成的知识体系，考虑到这一途径在自然界中的普遍存在，有关血红素生物合成的遗传信息令人惊讶地很少。

The regulation of heme biosynthesis in nitrogen-fixing soybean root nodules is being studied as a means of understanding how the bacterial symbiont Bradyrhizobium japonicum interacts with the plant to regulate metabolic processes essential for symbiosis. Bacterial heme is believed to be the prosthetic group of the plant nodule protein leghemoglobin, hence heme and apoprotein synthesis by the respective orgainism must be coordinated during leghemoglobin formation. Experiments will elucidate the exact role of the B. japonicum heme biosynthetic pathway in leghemoglobin formation, and deterine how heme synthesis genes are regulated during nodule development Specific objectives are to (i) isolate B. japonicum heme synthesis mutants, (ii) determine the effects of the bacterial heme synthesis lesions on leghemoglobin synthesis, (iii) isolate and characterize B. japonicum heme synthesis genes, and (iv) study the regulation of heme synthesis genes by nodule-associated factors and by bacterial regulatory protein. Finally, the regulation of bacterial heme synthesis will be correlated with leghemoglobin formation. Biological nitrogen fixation is important because it is an inexpensive and environmentally-sound source of nitrogen fertilizer. Understanding plant-microbe interactions at the molecular level is important in any attempt to improve the symbiosis or to extend it to other plants by genetic engineering. The study of the Bradyrhizobium japonicum/soybean interaction will provide a better understanding of interkingdom commmunication as well as contribute to the body of knowledge of heme biosynthesis in general, of which there is surprisingly little genetic information considering the ubiquity of this pathway in nature.