SEP 13, 2018 10:30 AM PDT

Studying Environmental Sensing and Response in a Bacterial Plant Pathogen - Inside Out

Speaker
  • Professor of Microbiology, Department of Biological Sciences, Virginia Tech
    Biography
      Dr. Ann Stevens is a Professor of Molecular Microbiology at Virginia Tech in Blacksburg, VA. She earned her Ph.D. in 1993 from the Dept. of Microbiology at the University of Illinois at Urbana-Champaign in the laboratory of Dr. Abigail Salyers. For the next four years, she served as a postdoctoral research associate at the University of Iowa under the supervision of Dr. E. Peter Greenberg. In 1997, she began a faculty position at Virginia Tech in the Department of Biological Sciences as an assistant professor and was promoted with tenure to associate professor in 2004 and full professor in 2010. Research in her laboratory is focused on environmental sensing and response as it relates to bacterial quorum-sensing systems and bacterial-host interactions. Model organisms under investigation include the plant pathogen Pantoea stewartii and the human/animal pathogen Vibrio parahaemolyticus. Dr. Stevens was a National Science Foundation CAREER award recipient. She has received the Virginia Tech Alumni and Wine Teaching Awards and is a member of the Virginia Tech Academies of Teaching Excellence and of Faculty Service.

    Abstract

    The bacterium Pantoea stewartii subsp. stewartii causes Stewart’s wilt disease in corn and serves as a model for other xylem-dwelling phytopathogens. P. stewartii is transmitted to plants via corn flea beetles where it first colonizes the apoplast causing water-soaked lesions, then migrates to the xylem and forms a biofilm that blocks water transport. P. stewartii uses quorum sensing to insure the exopolysaccharide production necessary for biofilm formation occurs only at high cell density during growth in the xylem. To gain broader insights into what genes are important for plant pathogens like P. stewartii during in planta growth, the bacteria were grown inside the xylem followed by genomic-level analyses in vitro.  RNA purified from in planta grown P. stewartii was used to determine the most highly expressed genes via RNA-Seq through Next-generation Illumina sequencing of cDNA. Analysis of the transcriptome data via gene ontology revealed that bacterial transporters and systems important for oxidation-reduction processes are highly expressed in response to the environment inside the plant.  A subsequent genomic-level Tn-Seq analysis was performed to identify bacterial genes essential for survival in planta. A mariner transposon library of approximately 40,000 mutants was constructed and used to inoculate corn seedlings through a xylem infection model. The Tn-Seq analysis suggested that over 400 genes are important for xylem survival. In planta competition assays and virulence assays have so far revealed important roles for outer membrane proteins and Lon protease in bacterial colonization, growth and/or virulence in the corn plant. These studies are giving us new insights into the lifestyle of a pathogenic plant bacterium when living inside its plant host.
     

    Learning Objectives: 

    1. Explain the role of quorum sensing during plant disease caused by the phytopathogen Pantoea stewartii subsp. stewartii.
    2. Design genome-levels experiments to study the expression and role in survival of bacterial genes during in planta growth.


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    SEP 13, 2018 10:30 AM PDT

    Studying Environmental Sensing and Response in a Bacterial Plant Pathogen - Inside Out


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