RESEARCH PGR: An interdisciplinary approach to deciphering molecular signaling pathways controlling plant-symbiont associations in legumes and cereals.

农作物的根部含有重要的微生物，这些微生物使植物和微生物能够满足其营养需求。这两种截然不同的生物之间的关系被称为共生关系，因为双方都从中受益。植物将阳光和二氧化碳转化为糖和其他有机化合物，供应给根部的微生物。这些微生物以植物容易吸收的形式为植物提供磷酸盐和氮。这些共生关系允许某些作物在不添加肥料的情况下生长。例如，植物无法将大气中的气态氮转化为可被纳入蛋白质、维生素和其他关键生物分子的还原形式，从而使它们能够发芽、发育和生长。某些作物，如豆科植物（如豆类、豌豆和苜蓿），在其根部的特殊结构中含有转化氮的细菌，这些细菌将这种还原氮提供给植物。大多数作物没有这些细菌，必须依靠氮肥的施用来实现最佳生长。该项目旨在从分子角度理解植物和微生物之间的共生关系，其长期目标是在玉米和小麦等非豆科作物中实现这种关系，这些作物目前需要大量施肥来维持作物产量。该项目的一个更广泛的影响是夏季植物蛋白质组学研讨会，它为整个植物研究界提供蛋白质组学和基因组分析方面的培训。本项目旨在研究模式豆科作物苜蓿（Medicago truncatula）和模式单子叶水稻（moncot）对共生微生物（固氮根瘤菌和丛枝菌根真菌）识别和响应的早期分子事件。这种方法将能够在分子水平上比较这两种作物组识别其有益微生物的机制。对这两个系统中共同的和不同的化学和遗传因素的分析应该提供工具和信息，以便能够在谷类作物（如水稻、玉米、小麦）和固氮根瘤菌之间建立有益的联系。具体目标是(1)在信号接收后的第一个小时内鉴定被磷酸化、乙酰化或泛素化修饰的宿主蛋白，并验证来自本次和之前项目奖励期的潜在活性候选蛋白；(2)利用信息学和计算模型，将蛋白质组学和转录组学反应整合到可以在两个物种中进行比较的网络中。(3)利用新开发的化学基因组芯片系统对共生因子进行高通量筛选。该项目将扩大植物蛋白质组学研讨会，培训最新的大规模蛋白质组学和基因组分析技术。

Part 1: Non-technical abstractThe roots of crop plants contain important microorganisms that allow the plants and microbes to satisfy their nutritional needs. The relationship between these two very different types of organisms is called symbiotic because both partners benefit from the association. The plant converts sunlight and carbon dioxide into sugars and other organic compounds that are supplied to the microbes in the roots. The microbes provide phosphate and nitrogen to the plant in forms that the plant can readily ingest. These symbiotic associations permit the growth of some crops without added fertilizer. For example, plants are unable to convert gaseous nitrogen in the atmosphere into a reduced form that can be incorporated into the proteins, vitamins and other critical biomolecules that allow them to germinate, develop and grow. Certain crops, such as the legumes (e.g., beans, peas and alfalfa) harbor nitrogen-converting bacteria within specialized structures in their roots that provide this reduced nitrogen to the plant. Most crops do not have these bacteria and must rely on the application of nitrogen fertilizer for optimal growth. This project seeks to obtain a molecular understanding of this symbiotic association between plant and microbes, with a long-term goal of enabling such an association in non-leguminous crops like corn and wheat, which currently require extensive fertilization to sustain crop yield. A broader impact of this project is a summer Plant Proteomics Workshop, which provides training in proteomic and genomic profiling to the entire plant research community.Part 2: Technical abstractThis project seeks to profile the early molecular events in the recognition of and response to symbiotic microbes (nitrogen-fixing rhizobia and arbuscular mycorrhizal fungi) by the model legume crop, Medicago truncatula and the model monocot, rice. This approach will enable a comparison at the molecular level of the mechanisms by which these two crop groups recognize their beneficial microbes. The analysis of the shared and distinct chemical and genetic factors in these two systems should provide tools and information to enable the engineering of beneficial associations between cereal crops (e.g., rice, corn, wheat) and nitrogen-fixing rhizobia. The specific aims are (1) the identification of host proteins modified by phosphorylation, acetylation or ubiquitinylation in first hour following signal reception, and validation of potentially active candidates from this and from the previous project award period, (2) the integration of proteomic and transcriptomic responses into networks that can be compared in the two species, using informatics and computational modeling, and (3) a high-throughput screen for symbiosis factors using a newly developed chemical genomics chip system. This project will expand a Plant Proteomics Workshop for training in the latest large-scale proteomic and genomic profiling technologies.