Osmoprotection of Pseudomonas Syringae During its Association with Plants: Role of the BetT and OpuC Transporters

为了应对环境中波动的渗透压，微生物经常产生转运体来吸收渗透保护剂化合物。这些化合物，包括甘氨酸甜菜碱及其前体胆碱，广泛存在于植物中；然而，人们对它们在植物菌群中的可用性知之甚少。通过转运体介导的吸收的渗透适应可能对植物相关细菌的生态学很重要，这是基于植物上微生物栖息地中水分有效性的大幅波动以及植物源性渗透保护剂的可能存在。了解这些化合物在细菌生态中的作用需要了解介导摄取的转运体。在丁香假单胞菌中发现了两种转运蛋白，它们负责高渗胁迫下甘氨酸甜菜碱及其前体胆碱的全部或绝大部分摄取。这种生物是一种叶面病原体，是常见的植物寄生物，是研究细菌与植物相互作用的模式生物。本项目旨在对BetT和OpuC这两种转运体进行表征，并评价它们在丁香假单胞菌渗透适应、生长和存活中的作用。为了实现这一目标，我们将研究BetT和OpuC的功能特征，包括它们的动力学参数和溶质特异性，研究它们在转录和转录后水平的调控，并确定它们在具有不同自然和操纵浓度渗透保护剂的植物上对丁香假单胞菌生态的意义。这一信息将有助于填补假单胞菌物种摄取介导的渗透适应信息的空白，并将为细菌如何如此熟练地利用它们所适应的生态位提供见解。这些研究中产生的知识与改善食品安全和生产有关，包括控制植物和动物病原体的策略，改进植物疾病预测和控制，以及预测转基因植物的非靶标效应，以增强对干旱和盐胁迫的耐受性。本项目将培养一名博士后研究员、一名研究生和四名本科生，其中至少有一名少数民族学生；为中学生和国际农业科学家举办的外展活动；以及微生物学本科课程强化活动。

To cope with fluctuating osmolarity in their environment, microorganisms often produce transporters for the uptake of osmoprotectant compounds. These compounds, including glycine betaine and its precursor choline, occur widely in plants; however, little is known of their availability to the plant microflora. Osmoadaptation via transporter-mediated uptake may be important to the ecology of plant-associated bacteria based on the large fluctuations in water availability in microbial habitats on plants and the likely presence of plant-derived osmoprotectants. Understanding the role of these compounds in bacterial ecology requires knowledge of the transporters that mediate uptake. Two transporters that are responsible for all, or the vast majority, of the uptake of glycine betaine and its precursor choline under hyperosmotic stress have been identified in Pseudomonas syringae. This organism is a foliar pathogen, a common plant resident, and a model organism for studying bacterial-plant interactions. The goal of this project is to characterize these two transporters, designated BetT and OpuC, and evaluate their role in the osmoadaptation, growth and survival of P. syringae in plants. To address this goal, the functional characteristics of BetT and OpuC, including their kinetic parameters and solute specificity, will be characterized, their regulation at the transcriptional and post-transcriptional levels will be examined, and their significance to P. syringae ecology on plants that have various natural and manipulated concentrations of osmoprotectants will be identified. This information will help fill a void of information on uptake-mediated osmoadaptation in Pseudomonas species and will provide insights into how bacteria so expertly exploit the ecological niches to which they are adapted. The knowledge generated in these studies is relevant to improving food safety and production, including strategies for controlling plant and animal pathogens on plants, improving plant disease forecasting and control, and predicting non-target effects of transgenic plants engineered for enhanced tolerance to drought and salinity stress. This project will contribute to education through training a postdoctoral researcher, a graduate student, and four undergraduate students, at least one of which is expected to be a minority student; outreach activities for secondary school students and international agricultural scientists; and curriculum strengthening activities for an undergraduate microbiology program.