Roles of a Rhizobium-induced Plant Peroxidase in Infection and Nodulation

9507535 VandenBosch固氮根瘤是在根瘤菌科细菌的感染下在豆科植物根部形成的，是植物在自然和农业环境中可利用的氮的关键来源。 由于其生态和经济的重要性，这种共生刺激了许多研究寄主植物和共生体之间的相互作用。 虽然关键的决定性事件的豆科植物/根瘤菌共生可能先于细菌感染，没有植物基因已被确定之前，强烈表达的感染和根瘤形态建成。 我们已经使用消减杂交，以丰富的植物基因诱导在此早期，感染前阶段的蒺藜苜蓿/苜蓿根瘤菌共生。 这样鉴定的一个基因编码假定的植物过氧化物酶，命名为MtRip 1，用于根瘤菌诱导的过氧化物酶。 Mtrip 1的诱导时间、定位和方式表明它可能对共生体的建立起关键作用。 虽然Rip 1蛋白在共生建立过程中的作用是不确定的，据推测，该酶可能是需要根瘤形态发生，和/或它可能是在逮捕根瘤菌感染，和/或它可能是一个水槽过氧化氢。 本项目的实验计划旨在使用几种互补的方法来研究根瘤菌诱导的过氧化物酶的功能。 这项工作的结果将使我们能够解决几个长期存在的问题，包括植物如何调节其共生根瘤菌的感染，以及根瘤菌如何避免引发植物病原体的广义防御反应。 更重要的是，这项研究将促进我们对发育过程中细胞壁变化的功能后果的理解。

9507535 VandenBosch Nitrogen-fixing root nodules, which form on legume roots in response to infection with bacteria in the family Rhizobiaceae, are a key source of nitrogen available to plants in both natural and agricultural environments. Because of its ecological and economic importance, this symbiosis has stimulated many studies into the interactions between host plant and symbiont. Although key determinative events of the legume/Rhizobium symbiosis are likely to precede bacterial infection, no plant genes have been identified previously that are expressed strongly prior to infection and nodule morphogenesis. We have used subtractive hybridization to enrich for plant genes induced during this early, pre-infection phase of the Medicago truncatula /Rhizobium meliloti symbiosis. One gene so identified encodes a putative plant peroxidase, named MtRip1 for Rhizobium-induced peroxidase. The timing, localization and manner of induction of Mtrip1 indicate that it may be of key importance to symbiotic establishment. Although the role of the Rip1 protein during symbiotic establishment is uncertain, it is hypothesized that the enzyme may be required for nodule morphogenesis, and/or it may be used during arrest of rhizobial infection, and/or it may be a sink for hydrogen peroxide. The experimental plan of this project is designed to investigate the function(s) of the Rhizobium-induced peroxidase using several complementary approaches. The outcome of this work will allow us to address several long-standing questions in nodulation research, including how the plant regulates infection by its symbiont Rhizobium, and how Rhizobium avoids triggering a generalized defense response as occurs in response to plant pathogens. More fundamentally, the research will advance our understanding of the functional consequences of changes in cell walls during development.