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Publication Date


Document Type

Honors Project




Pseudomonas syringae, Nicotiana, Pathogenic microorganisms, Virulence (Microbiology), Plants


Pseudomonas is a family of gram-negative bacteria that are pathogenic to many plant species. In the host apoplast, Pseudomonas secretes a host of effector proteins into the plant cell via a type III secretion system, which subvert the host basal immune response and allow the bacteria to proliferate. Of all the catalogued effectors, AvrPto is most extensively studied because some plants appear to have machinery to recognize it, which boosts the plant immune system and combats the infection. AvrPto has several distinct functional domains that are also identification sites for plant recognition machinery. This research focuses on the recent discovery of the C-terminal domain (CTD), a region on AvrPto that is recognized by tobacco. Recognition is dependent upon in vivo phosphorylation of CTD residues S147 and S149, so the putative recognition protein is termed Rpa for Resistance to Phosphorylated AvrPto. The identity of Rpa and the virulence function of the CTD have yet to be determined. To determine the native function of the CTD, site-based mutations of residues 147 and 149 were tested in native tobacco, N. sylvestris, and N. glutinosa, a species that we hypothesized lacks Rpa. We report an idiosyncrasy in the recognition machinery of N. glutinosa, suggesting that anionic character is not as important for CDT-recognition in this species. In the second part of this thesis, we report that N. sylvestris recognizes both glutamic acid and cysteine substitutions at residues 147 and 149., while disease assays suggest that N. glutinosa only recognizes the cysteine substitution. This suggests that anionic character is not essential for CTD recognition in either species since cysteine is not typically charged or phosphorylatable. Determining the modification status of cysteine in vivo will be necessary to confirm this conclusion.




xii, 101 p. : ill. (some col.) Honors project-Smith College, Northampton, Mass., 2012. Includes bibliographical references (p. 93-101)