Gene regulation in bacteria is highly complex and requires the activity of sigma
factors that function as transcriptional regulators. In Pseudomonas syringae pv. syringae
B728a, 14 sigma factors have been identified. One of the more interesting is rpoN,
encoding Sigma 54, which was initially described for its role in nitrogen utilization and
later shown to be involved in regulating adhesion, motility, toxin production, and
pathogenicity. The only commonality identified amongst these genes is that gene
regulation by Sigma 54 is not essential for normal growth and development because
mutational inactivation of rpoN is not lethal. Unlike Sigma 70, which recognizes
promoter sites located at positions -10/-35 upstream of the transcription initiation site,
Sigma 54 recognizes sites located at positions -12/-24. P.s. pv. syringae B728a encodes
an RpoN that shares 80-98% identity with other Pseudomonas species. Promoter scans
were conducted on the B728a genome to look for probable binding sites of RpoN.
Analysis revealed that RpoN may be involved in regulating genes encoding ABC
transporters, drug efflux pumps, flagella proteins, nitrate transporters, and several regulatory proteins. An insertional mutation in the rpoN gene was constructed in the
B728a genome and a phenotypic analysis was initiated. Decreased swarming and
adhesion ability of the rpoN mutant was observed as compared to B728a. The ability to
utilize sole nitrogen sources was also affected. The rpoN mutant showed little or no
growth on sole nitrogen sources such as alanine, histidine, lysine, and serine.
Pathogenicity was shown to require a functional RpoN, as both HR and disease
development was effected by an rpoN mutation. Pseudomonas syringae pv. syringae is
most known for the production of two phytotoxins. Unlike RpoN in other species, in
P.s. pv. syringae B728a it appears to indirectly down regulate toxin production of
syringomycin and syringopeptin. The goal of this study was to characterize some of the
important roles RpoN is known to possess and to understand its role in the plant
pathogenic and epiphytic lifestyle of P. s. pv. syringae B728a.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-308 |
| Date | 2009 May 1900 |
| Creators | Lorge, Amber L. |
| Contributors | Gross, Dennis |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | application/pdf |
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