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

以前的研究表明，只有一小部分的 固氮根瘤菌在豆科植物根部引起的侵染 成功地形成了结节。 由于未知的原因，大多数 启动在整个过程完成之前终止 发展阶段 植物激素乙烯 显示抑制结节形成。 相反， 彼得博士的实验室已经表明，结节的数量 苜蓿根瘤菌在苜蓿根上的形成量显著高于对照 暴露于1-a-氨基-乙氧基乙烯基甘氨酸（AVG）后增加，a 乙烯生物合成的有效抑制剂。 所有这些 结果表明，乙烯生物合成可能具有重要的 调节感染和结节效率的作用 阵 这种可能性与以下事实相一致： 许多慢生根瘤菌菌株合成一种结构 和AVG的功能类似物。 该化合物，称为 根瘤菌毒素也是乙烯的有效抑制剂 植物的生物合成。 PI将检查以下方面的作用： 根瘤菌毒素和乙烯生物合成对根瘤的调控 发展 B的突变体。失去了 合成根瘤菌毒素将被分离并接种到 寄主植物分析根瘤毒素对乙烯的影响 生物合成和根瘤发育。 PI将决定 根瘤菌毒素和AVG是否通过 增加感染总数或减少 感染流产。 根瘤菌毒素合成所需基因 将被分离并鉴定。 虽然所有的植物都需要氮来生长，但只有少数 植物（主要是豆类）可以吸收大气中的氮， 将其转化为可用的氮化合物。 本研究将 研究豆科植物启动氮的机制 固定过程，使这些植物生长没有 与氮有关的经济和环境成本 受精

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.