Title: Genome-Enabled Analyses of Natural Populations of Pathogens on Natural Hosts
PI: Amy Charkowski, University of Wisconsin
Co-PIs: Sarah Grant and Jeff Dangl, University of North Carolina;
Nicole Perna and Ching-Hong Yang, University of Wisconsin
Collaborators: Alvin Bussan, University of Wisconsin-Madison;
Jose Caram de Souza and Haiko Enok Sawazaki, Inst. Agr. de Campinas, Brazil
Hamed Mazyad, Agricultural Research Center, Egypt

Intellectual Merit. Little is known about molecular host-pathogen interactions in natural settings. The goals of this project are to examine the presence, expression and function of virulence genes in a pathogen on its natural hosts to determine how they are affected by host and environmental factors. We also will examine the population dynamics of this pathogen in wild relatives of the crop species along the natural range of these hosts. We chose the bacterial plant pathogen, Erwinia carotovora as the model pathogen because: 1) it is one of the most important and common bacterial plant pathogens; 2) two genome sequences are available from different strains of Erwinia, and 3) genetic tools are available for this pathogen. We chose potatoes as the main model host plant because 1) recent epidemiological analyses have provided a variety of different Erwinia isolates that infect potatoes in North America and 2) potato fields are clonal, providing a contrasting environment to populations of natural plants. We intend to compare and contrast a suite of virulence factors present in strains from diverse environments to address how host plants affect virulence gene content, evolution, and expression. The diverse interdisciplinary team assembled for this project includes scientists who specialize in molecular biology, microbiology, plant-microbe interactions, plant genetics, microbial genomics, microbial evolution, plant ecology, global positioning systems, and epidemiology.

The type III protein secretion system (TTSS) of various Gram-negative animal and plant pathogens delivers type III effector proteins into eukaryotic host cells and these proteins are required by many plant pathogens, including Erwinia, for full virulence on plants. In this project, we will identify type III effectors secreted by multiple E. carotovora strains isolated from potatoes and wild hosts to determine if multiple classes of effectors are present. We will use quantitative PCR and microarrays to measure effector content and expression in isolates from North and South America. A highly virulent E. carotovora strain will be used for field studies to determine if TTSS and effector mutants are able to grow and/or survive on potatoes and wild plants under natural conditions. We will also examine naturally-infected plants from North and South America to determine if similar effectors are present and expressed in locations that differ in climate, soil type, wild hosts, and water sources. Finally, wild plant species will be examined to identify disease resistance genes whose function is triggered by the presence of specific E. carotovora type III effector proteins. These will be tested to determine if the plant species with these resistance genes are indeed more resistant to E. carotovora strains carrying the corresponding type III effectors.

Broader Impact. This work will provide a model system, and genomic tools to examine, for the first time, virulence gene expression, population, diversity, and evolution in an important enterobacterial pathogen on multiple natural hosts in multiple environments. All sequence and experimental data generated will be deposited in a web-based database accessible to others in the scientific community for re-analysis and for the development of further research and teaching tools. This project will foster collaborations among a diverse and multidisciplinary group of scientists from five institutions in three countries. We will train undergraduates and graduate students, as well as postdoctoral researchers in this multidisciplinary project from a variety of institutions.

This material is based upon work supported by the National Science Foundation under Grant No. 0412599. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

 

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