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Browsing by Author "Reynoso, Guadalupe"

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    The in planta role of the global regulator Lrp in the bacterial phytopathogen Pantoea stewartii subsp. stewartii
    Reynoso, Guadalupe (Virginia Tech, 2022-01-19)
    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.
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    The Transcription Factor Lrp of Pantoea stewartii subsp. stewartii Controls Capsule Production, Motility, and Virulence Important for in planta Growth
    Bartholomew, Holly P.; Reynoso, Guadalupe; Thomas, Brandi J.; Mullins, Chase M.; Smith, Chastyn; Gentzel, Irene N.; Giese, Laura A.; Mackey, David; Stevens, Ann M. (Frontiers, 2022-02-14)
    The bacterial phytopathogen Pantoea stewartii subsp. stewartii causes leaf blight and Stewart's wilt disease in susceptible corn varieties. A previous RNA-Seq study examined P. stewartii gene expression patterns during late-stage infection in the xylem, and a Tn-Seq study using a P. stewartii mutant library revealed genes essential for colonization of the xylem. Based on these findings, strains with in-frame chromosomal deletions in the genes encoding seven transcription factors (NsrR, IscR, Nac, Lrp, DSJ_00125, DSJ_03645, and DSJ_18135) and one hypothetical protein (DSJ_21690) were constructed to further evaluate the role of the encoded gene products during in vitro and in planta growth. Assays for capsule production and motility indicate that Lrp plays a role in regulating these two key physiological outputs in vitro. Single infections of each deletion strain into the xylem of corn seedlings determined that Lrp plays a significant role in P. stewartii virulence. In planta xylem competition assays between co-inoculated deletion and the corresponding complementation or wild-type strains as well as in vitro growth curves determined that Lrp controls functions important for P. stewartii colonization and growth in corn plants, whereas IscR may have a more generalized impact on growth. Defining the role of essential transcription factors, such as Lrp, during in planta growth will enable modeling of key components of the P. stewartii regulatory network utilized during growth in corn plants.