Signaling Dynamics in Pseudomonas syringae pv. tomato DC3000
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Fishman, Max Robert
Pseudomonas syringae pv. tomato DC3000 (Pto) is thought to encounter disparate environments during epiphytic and endophytic growth. In order to be successful during pathogenesis, Pto must recognize when it enters the leaf apoplast and then regulate the appropriate genes. In bacteria, two-component systems (TCSs) commonly sense environmental changes and modulate gene regulation to suit that environment. The leaf apoplast is relatively abundant in Ca2+ in comparison to the leaf surface. The TCS, CvsSR, in Pto is a regulatory system that is induced by Ca2+ and regulates virulence of Pto in tomato and Arabidopsis. The global virulence regulators hrpR, hrpS, and hrpL are among the genes that CvsSR regulate. Its role in virulence is partially explained through its regulation of these genes and also through its regulation of the gene PSPTO_5255, which encodes a carbonic anhydrase. Deletion of PSPTO_5255 reduces virulence of Pto on tomato and also delays the hypersensitive response caused by Pto on Nicotiana benthamiana. PSPTO_5255 was a previously uncharacterized virulence gene in Pto and the mechanism by which it affects virulence is still unclear. Bacteria may induce precipitation of calcium upon exposure to increases in external Ca2+ concentration. Several Pseudomonas species and strains induce precipitation of calcium phosphate in the external environment surrounding the bacterial colony. Calcium phosphate precipitation on the surface of bacterial cells was variable among Pseudomonas strains. Pto is among the strains that does not normally precipitate calcium phosphate on the surface of cells. Multiple genes are involved in Pto calcium phosphate precipitation, including ones that suppress surface-associated calcium phosphate precipitation in Pto. The genes cvsS and cvsR are among the genes that suppress surface-associated calcium phosphate precipitation in Pto. In the ∆cvsS and ∆cvsR strains, this process is partially dependent on the CvsSR regulated genes PSPTO_5255 and PSPTO_5256. Constitutive expression of PSPTO_5255 and PSPTO_5256 in the ∆cvsS and ∆cvsR strains suppress surface-associated calcium phosphate precipitation. This suggests that Pto utilizes secretion of bicarbonate or carbonic acid to keep calcium phosphate from accumulating on the surface of cells.
Supplemental file(s) description: Table 6.1, Table 6.16, Table 6.19, Table 7.1
Plant pathology; calcium precipitation; carbonic anhydrase; pathogen; Pseudomonas; two component system; virulence
Filiatrault, Melanie J.
Helmann, John D.; Collmer, Alan Raymond; Kochian, Leon V.
Plant Pathology and Plant-Microbe Biology
Ph. D., Plant Pathology and Plant-Microbe Biology
Doctor of Philosophy
dissertation or thesis