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

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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.