Cellular Responses to Quaternary Ammonium Compounds by Pseudomonas Syringae that Influence its Interactions with Plants

智力优势 植物被多种微生物定殖，包括许多影响植物和环境健康的微生物。 植物产生一类称为季铵化合物（QAC）的化合物，其对植物膜以及植物对干旱和盐胁迫的耐受性很重要。 这些化合物，包括甜菜碱，肉毒碱和胆碱，也可能有利于植物相关的细菌。 例如，甜菜碱可以保护压力，胆碱可以作为一些细菌膜脂质的构建块，胆碱-O-硫酸盐可以帮助储存硫。 大多数植物相关细菌，包括植物病原体假单胞菌，不能合成QAC，因此依赖于宿主的生产。 因此，这些生物可能进化出了输入和利用这些化合物的机制。 为了支持这一点，运输胆碱的能力最近被证明在植物定殖期间为P. dichloringae提供了明显的适应性益处。 此外，表征用于胆碱和甜菜碱摄取的全套P. dichloringae转运蛋白的研究确定了可能参与QAC代谢和调节的额外的新细胞组分。 该项目的目标是表征P. dallingae对特定植物来源的QAC的反应，并评估这些反应如何影响P. dallingae与植物的相互作用。 为了解决这些目标，首先，肉毒碱将被检查作为一种引诱剂和营养源，通过调查的作用，一个新发现的肉毒碱响应趋化蛋白在指导细菌运动发芽幼苗，并确定所需的基因肉毒碱catenase和他们的贡献健身。 第二，胆碱-O-硫酸盐将作为硫和营养物质的来源进行评估，通过表征运输和催化剂的损失如何影响植物上的P. pallingae健身，并通过更广泛地表征参与胆碱-O-硫酸盐吸收的细胞组分。 第三，甜菜碱，胆碱，磷酰胆碱和磷脂酰胆碱将作为细菌的信号分子，通过检查缺乏降解单个化合物的能力，从而能够积累它们的P. lingae突变体中的全局基因表达模式进行评估。 这些研究将显著推进我们对P. dichloringae对这类特殊化合物的感知，信号传导和代谢如何影响这种广泛研究的细菌病原体定殖植物的能力的理解。 与植物相关的P. pallingae种群不仅是植物疾病病原体的储存库，而且也是生物冰核的储存库，可能在导致降雨的大气过程中发挥作用。 深入了解QAC对叶相关细菌种群的影响具有及时的重要性，因为干旱的增加，如全球气候变化模型所预测的那样，以及盐碱化，如在大面积灌溉农田中发生的那样，可能导致植物组织中QAC丰度增加，这是由于自然积累或农业工程提高干旱和盐碱耐受性。 更广泛的影响 该项目将通过为一名研究生提供培训和为至少五名本科生提供重要的研究经验来促进教育，其中一些学生预计将是科学领域代表性不足的群体的成员。 外联活动将通过爱荷华州州立大学的生物学教师既定方案，为两名生物学教师（7 - 12年级）提供实习机会，随后共同开发和实施基于细菌冰核和叶片定植的发现课程。 外联活动还将包括指导至少两个讲习班，通过爱荷华州州立大学的科学约束计划，促进来自科学代表性不足群体的中学生的参与，并共同指导一个针对小学生及其家长的植物病原体讲习班。

Intellectual Merit Plants are colonized by a diversity of microorganisms, including many that influence plant and environmental health. Plants produce a class of compounds called quaternary ammonium compounds (QACs) that are important to plant membranes and to plant tolerance to drought and salinity stress. These compounds, including betaine, carnitine, and choline, may also benefit plant-associated bacteria. For example, betaine can confer protection to stresses, choline can serve as a building block for some bacterial membrane lipids, and choline-O-sulfate may help store sulfur. Most plant-associated bacteria, including the plant pathogen Pseudomonas syringae, cannot synthesize QACs and thus are dependent on production by the host. Consequently, these organisms have likely evolved mechanisms to import and exploit these compounds. In support of this, the ability to transport choline was recently shown to provide a clear fitness benefit to P. syringae during its colonization of plants. Moreover, studies characterizing the full set of P. syringae transporters for choline and betaine uptake identified additional novel cellular components that may be involved in QAC metabolism and regulation. The goals of this project are to characterize the responses of P. syringae to specific plant-derived QACs and evaluate how these responses influence P. syringae interactions with plants. To address these goals, first, carnitine will be examined as an attractant and nutrient source by investigating the role of a newly identified carnitine-responsive chemotaxis protein in directing bacterial movement to germinating seedlings, and by identifying the genes required for carnitine catabolism and their contribution to fitness. Second, choline-O-sulfate will be evaluated as a source of sulfur and nutrients by characterizing how the loss of transport and catabolism impact P. syringae fitness on plants and by more extensively characterizing the cellular components involved in choline-O-sulfate uptake. And third, betaine, choline, phosphorylcholine and phosphatidylcholine will be evaluated as signal molecules for bacteria by examining global gene expression patterns in P. syringae mutants that lack the ability to degrade individual compounds and thus are able to accumulate them. These studies will significantly advance our understanding of how the perception, signaling and metabolism of this special class of compounds by P. syringae influences the ability of this widely studied bacterial pathogen to colonize plants. Plant-associated P. syringae populations are relevant not only as reservoirs of pathogens for plant disease, but also as reservoirs of biological ice nuclei that may have a role in atmospheric processes leading to rain. Insights into the impact of QACs on leaf-associated bacterial populations are of timely importance because increases in drought, as predicted by global climate change models, and salinity, as is occurring in large areas of irrigated agricultural lands, can result in increased QAC abundance in plant tissues, due to either natural accumulation or agricultural engineering to improve drought and salinity tolerance. Broader Impacts This project will contribute to education by providing training for one graduate student and significant research experiences for at least five undergraduate students, several of which are expected to be members of under-represented groups in the sciences. Outreach activities will provide internships for two biology teachers (7th-12th grade) through an established program at Iowa State University for biology teachers, with the subsequent co-development and implementation of discovery-based curricula based on bacterial ice nucleation and leaf colonization. Outreach activities will also include directing at least two workshops to advance the involvement of middle school students from under-represented groups in the sciences through the Science Bound program at Iowa State University, and co-directing a workshop on plant pathogens for elementary students and their parents.