New hypotheses about the origin of Pseudomonas syringae crop pathogens

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dc.contributor.authorCai, Rongmanen
dc.contributor.committeechairVinatzer, Boris A.en
dc.contributor.committeememberKim, Inyoungen
dc.contributor.committeememberJelesko, John G.en
dc.contributor.committeememberLeman, Scotland C.en
dc.contributor.departmentPlant Pathology, Physiology, and Weed Scienceen
dc.date.accessioned2014-03-14T21:11:03Zen
dc.date.adate2012-05-31en
dc.date.available2014-03-14T21:11:03Zen
dc.date.issued2012-05-02en
dc.date.rdate2012-05-31en
dc.date.sdate2012-05-13en
dc.description.abstractPseudomonas syringae is a common foliar plant pathogenic bacterium that causes diseases on many crop plants. We hypothesized that today's highly virulent P. syringae crop pathogens with narrow host range might have evolved after the advent of agriculture from ancestral P. syringae strains with wide host range that were adapted to mixed plant communities. The model tomato and Arabidopsis pathogen P. syringae pv. tomato (Pto) DC3000 and its close relatives isolated from crop plants were thus selected to unravel basic principles of host range evolution by applying molecular evolutionary analysis and comparative genomics approaches. Phylogenetic analysis was combined with host range tests to reconstruct the host range of the most recent common ancestor of all analyzed strains isolated from crop plants. Even though reconstruction of host range of the most recent common ancestor of all analyzed strains was not conclusive, support for this hypothesis was found in some sub-groups of strains. The focus of my studies then turned to Pto T1, which was found to represent the most common P. syringae lineage causing bacterial speck disease on tomato world-wide. Five genomes were sequenced and compared to each other. Identical genotypes were found in North America and Europe suggesting frequent pathogen movement between these continents. Moreover, the type III-secreted effector gene hopM1 was found to be under strong selection for loss of function and non-synonymous mutations in the fliC gene allowed to identify a region that triggers plant immunity. Finally, Pto T1 was compared to closely related bacteria isolated from snow pack and surface water in the French Alps. Recombination between alpine strains and crop strains was inferred and virulence gene repertoires of alpine strains and crop strains were found to overlap. Alpine strains cause disease on tomato and have relatively wider host ranges than Pto T1. The conclusion from these studies is that Pto T1 and other crop pathogens may have evolved from ancestors similar to the characterized environmental strains isolated in the French Alps by adapting their effector repertoire to individual crops becoming more virulent on these crops but losing virulence on other plants.en
dc.description.degreePh. D.en
dc.identifier.otheretd-05132012-234836en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-05132012-234836/en
dc.identifier.urihttp://hdl.handle.net/10919/37806en
dc.publisherVirginia Techen
dc.relation.haspartCAI_R_D_2012.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectancestral state reconstructionen
dc.subjectfliCen
dc.subjecthost range evolutionen
dc.subjectPseudomonas syringaeen
dc.subjectmolecular evolutionen
dc.subjectHopM1en
dc.subjectrecombinationen
dc.subjectphylogeographyen
dc.subjectmicroevolutionen
dc.subjectmost recent common ancestoren
dc.subjectphylogenetic treeen
dc.subjectpopulation geneticsen
dc.titleNew hypotheses about the origin of Pseudomonas syringae crop pathogensen
dc.typeDissertationen
thesis.degree.disciplinePlant Pathology, Physiology, and Weed Scienceen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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