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

9507535 VandenBosch固氮根瘤是植物在自然和农业环境中可利用的氮素的主要来源，它在豆科植物根部形成，以应对根瘤科细菌的感染。由于其生态和经济的重要性，这种共生关系激发了许多关于寄主植物和共生体之间相互作用的研究。虽然豆科植物/根瘤菌共生的关键决定事件可能先于细菌侵染，但尚未鉴定出在侵染和根瘤形态发生之前强烈表达的植物基因。我们使用消减杂交来丰富在元宝紫花苜蓿/紫花苜蓿根瘤菌共生的早期、感染前阶段诱导的植物基因。这样发现的一个基因编码一种可能的植物过氧化物酶，名为MtRip1，意为根瘤菌诱导的过氧化物酶。Mtrip1的诱导时机、定位和诱导方式表明，它可能对共生关系的建立至关重要。虽然RIP1蛋白在共生建立过程中的作用尚不确定，但可以推测该酶可能是根瘤形成所必需的，和/或它可能用于阻止根瘤菌的侵染，和/或它可能是过氧化氢的汇。本项目的实验计划是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(S)。这项工作的结果将使我们能够解决结瘤研究中的几个长期存在的问题，包括植物如何调节其共生菌根瘤菌的感染，以及根瘤菌如何避免触发对植物病原体的普遍防御反应。更根本的是，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.