Role of Exopolysaccharides in Sinorhizobium meliloti/Alfalfa Symbiosis.

胞外多糖在苜蓿中华根瘤菌/苜蓿共生中的作用。

• 批准号: 0517162
• 负责人: Juan Gonzalez
• 金额: --
• 依托单位: University of Texas at Dallas
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-09-01 至 2010-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0517162&HistoricalAwards=false
• 关键词: Role; Exopolysaccharides; Sinorhizobium; meliloti; Alfalfa

The symbiotic interaction between the bacterium Sinorhizobium meliloti and its leguminous host plant is a very specific relationship involving metabolic co-operation between the two partners. The end result of this association is the fixation of atmospheric nitrogen by the symbiont for the benefit of the host. This interaction is highly dependent on the release and recognition of signal molecules produced by each partner. The main goal of this project is to determine how production of one of these signal molecules, the bacterially produced exopolysaccharides, is regulated and coordinated during the symbiotic process. S. meliloti produces at least two exopolysaccharides (succinoglycan and EPS II) that serve as invasion signals during the bacterial-plant interaction. Previous research has demonstrated that specific low molecular weight forms of these exopolysaccharides need to be generated by the bacterium to enable their role as signal molecules. More recently the researchers discovered and characterized three quorum-sensing systems (Mel, Sin/ExpR and Tra) in S. meliloti and showed that at least one of these (the Sin/ExpR system) plays an important role in exopolysaccharide production and nodulation. This project will explore how the biosynthesis of the symbiotically important exopolysaccharides of S. meliloti and the production of their active low molecular weight forms are regulated and coordinated. It is increasingly evident that the exopolysaccharides produced by S. meliloti play specific roles in the development of the root nodule symbiosis between the bacteria and legumes, particularly at the level of nodule invasion. Several interesting questions remain to be answered, including: under what environmental conditions are the different forms of the symbiotically active exopolysaccharides produced and how the production of these different forms are regulated and coordinated in the symbiont. The answers to these and related questions will lead to a greater understanding of the signaling mechanisms between symbiotic partners and the use of carbohydrates as signals. Further analyses of the functions of exopolysaccharides in the S. meliloti/Medicago sativa symbiosis may also provide insight into the possible uses of oligosaccharides as signaling molecules in other biological systems.Broader Impacts: The project will continue its multiple outreach activities, including among others, a Sinorhizobium project teaching laboratory, a lecture series to minority students and a collaboration project between the Dallas area science museums and the University of Texas at Dallas.

紫花苜蓿中华根瘤菌与其豆科寄主植物之间的共生相互作用是一种非常特殊的关系，涉及两者之间的代谢合作。这种结合的最终结果是，为了宿主的利益，共生体固定了大气中的氮。这种相互作用高度依赖于每个伴侣产生的信号分子的释放和识别。这个项目的主要目标是确定在共生过程中，这些信号分子之一--细菌产生的胞外多糖--的产生是如何调节和协调的。紫花苜蓿在细菌-植物相互作用过程中至少产生两种胞外多糖(琥珀多糖和EPS II)，作为入侵信号。以前的研究已经证明，这些胞外多糖的特定低分子形式需要由细菌产生，以使它们能够作为信号分子发挥作用。最近，研究人员在苜蓿中发现并鉴定了三个群体感应系统(MEL、Sin/Expr和Tra)，并表明其中至少一个系统(Sin/Expr系统)在胞外多糖的生产和结瘤过程中发挥着重要作用。本项目将探索如何调节和协调苜蓿共生重要胞外多糖的生物合成及其活性低分子形式的生产。越来越明显的是，紫花苜蓿产生的胞外多糖在细菌与豆科植物根瘤共生的发育过程中发挥着特殊的作用，特别是在根瘤入侵水平上。一些有趣的问题仍有待回答，包括：在什么环境条件下产生不同形式的共生活性胞外多糖，以及这些不同形式的胞外多糖的产生是如何在共生体中调节和协调的。对这些问题和相关问题的回答将使我们更好地理解共生伙伴之间的信号机制，并使用碳水化合物作为信号。进一步分析胞外多糖在紫花苜蓿/紫花苜蓿共生中的功能也可能为低聚糖在其他生物系统中作为信号分子的可能用途提供洞察。广泛影响：该项目将继续其多项外展活动，包括中华根瘤菌项目教学实验室，针对少数族裔学生的系列讲座，以及达拉斯地区科学博物馆和德克萨斯大学达拉斯分校的合作项目。