Effects of Ethylene on Nodule Development and Cloning of the Rhizobitoxine Genes

以前的研究表明，只有一小部分由固氮根瘤菌在豆科植物根部引发的感染成功地发展成根瘤。由于未知的原因，大多数启动在开发的所有阶段完成之前就终止了。植物激素乙烯已被证明能抑制根瘤的形成。相反，Peter博士实验室的研究表明，暴露于1-a-氨基-乙氧基乙烯甘氨酸（AVG）（一种有效的乙烯生物合成抑制剂）后，苜蓿根部由meliloti根瘤菌形成的根瘤数量显著增加。总之，这些结果表明乙烯生物合成可能在调节感染效率和结核形成方面发挥重要作用。这种可能性与许多日本慢生根瘤菌在结构和功能上合成AVG类似物的事实是一致的，这种化合物被称为根瘤菌毒素，也是植物中乙烯生物合成的有效抑制剂。该项目将研究根瘤素和乙烯生物合成在调节根瘤发育中的作用。本研究将分离失去合成根瘤素能力的突变体，并将其接种到寄主植物上，分析根瘤素对乙烯生物合成和根瘤素发育的影响。PI将确定根瘤素和AVG是否通过增加感染总数或减少感染流产来促进结节形成。根霉毒素合成所需的基因将被分离和鉴定。虽然所有植物的生长都需要氮，但只有少数植物（主要是豆科植物）能吸收大气中的氮并将其转化为可用的氮化合物。本研究将探讨豆科植物启动固氮过程的机制，使这些植物在没有与氮肥相关的经济和环境成本的情况下生长。

Previous studies have shown that only a small fraction of the infections initiated in legume roots by nitrogen-fixing rhizobia successfully develop into nodules. For unknown reasons, most initiations terminate prior to completion of the process at all stages of development. The plant hormone ethylene has been demonstrated to inhibit nodule formation. Conversely, studies in Dr. Peter's laboratory have shown that the number of nodules formed on alfalfa roots by Rhizobium meliloti is significantly increased by exposure to 1-a-amino-ethoxyvinylglycine (AVG), a potent inhibitor of ethylene biosynthesis. Together, these results suggest that ethylene biosynthesis may have an important role in regulating the efficiency of infection and nodule formation. This possibility is consistent with the fact that many strains of Bradyrhizobium japonicum synthesize a structural and functional analog of AVG. This compund, called rhizobitoxine, is also a potent inhibitor of ethylene biosynthesis in plants. The PI will examine the role of rhizobitoxine and ethylene biosynthesis in regulation of nodule development. Mutants of B. japonicum that have lost the ability to synthesize rhizobitoxine will be isolated and inoculated onto host plants to analyze the effects of rhizobitoxine on ethylene biosynthesis and nodule development. The PI will determine whether rhizobitoxine and AVG enhance nodule formation by increasing the total number of infections or by reducing infection abortion. Genes required for rhizobitoxine synthesis will be isolated and characterized. Although all plants require nitrogen for growth, only a few plants (legumes mostly) can take atmospheric nitrogen and convert it to useable nitrogen compounds. The present research will examine the mechanism by which legumes initiate the nitrogen fixation process, allowing those plants to grow without the economic and environmental cost associated with nitrogen fertilization.