Pantoea stewartii subsp. stewartii is a bacterial phytopathogen that causes the disease Stewart's wilt in corn. The insect vector Chaetocnema pulicaria, the corn flea beetle, transmits P. stewartii into corn plants through wounds in the leaves. The bacteria can then move to the xylem of the plant where they form a biofilm that inhibits the flow of water. A previous in planta RNA-Seq study resulted in the selection of lrp as a gene of interest for further analyses. A reverse genetics approach was used for the creation of a strain containing the in-frame deletion of lrp, as well as a revertant strain. The strain with the deletion of the lrp gene showed reduced motility and capsule formation when in vitro assays were conducted. It has previously been demonstrated that these characteristics are both important for the bacteria's ability to form a biofilm in the xylem of corn plants and produce disease symptoms. The in planta virulence and competition assays demonstrated that the lrp gene deletion also results in reduced disease symptoms in infected corn plants, as well as an inability to outcompete wildtype P. stewartii in xylem colonization.
In a bioinformatics approach, the transcriptional regulator Lrp of P. stewartii was present in the same node of the phylogeny as homologues from other closely related phytopathogens. This demonstrates that Lrp from P. stewartii and such homologues have evolved from a recent common ancestral gene. Examining the genomic islands present in P. stewartii, it is possible to begin to predict where some of the genes which have functions involved in plant colonization may have originated.
Overall, the results collected from the studies in this thesis contribute to improving understanding of how P. stewartii is successful at colonizing the xylem of corn plants and cause disease. This research could result in the development of methods to decrease crop susceptibility to infection with P. stewartii. / Master of Science / Stewart's wilt is a disease of corn plants caused by the bacterium Pantoea stewartii subsp. stewartii via the insect vector Chaetocnema pulicaria, the corn flea beetle. This infection has proven to be costly as it impacts the health of corn crops and impedes the export of corn seeds from varieties that are susceptible to infection by P. stewartii. The focus of the research conducted for this thesis has been on learning more about how specific P. stewartii genes impact the ability of the bacterium to colonize corn plants and cause Stewart's wilt disease symptoms. The information collected from this study is important for developing a better understanding of how wilt disease-causing pathogens are able to successfully infect plants, as well as for developing future treatments to prevent further infection of corn plants. In addition, preliminary bioinformatics work has shown that some of the P. stewartii genes of interest share a common ancestor with select genes from other known plant pathogens. Additional preliminary bioinformatics work on regions of the DNA called genomic islands has revealed where some genes of importance to the bacterium's ability to colonize plants may have originated. Overall, the work presented in this thesis contributes to improving our understanding of the roles that different parts of the P. stewartii genome have in allowing the bacterium to successfully colonize and cause disease in corn plants.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/107806 |
| Date | 19 January 2022 |
| Creators | Reynoso, Guadalupe |
| Contributors | Biological Sciences, Stevens, Ann M., Popham, David L., Aylward, Frank O., Vinatzer, Boris A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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