Regulation of amylovoran biosynthesis in Erwinia amylovora

Fire blight, caused by the gram-negative bacterium Erwinia amylovora, is one of the most devastating bacterial diseases for the apple and pear industry. Two pathogenicity factors strictly required for E. amylovora to cause disease are the exopolysaccharide amylovoran and the type III secretion system. In bacteria, the two-component signal transduction (TCST) system is the major paradigm to sense environmental stimuli and usually respond by regulating gene expression. One of the extensively studied TCSTs in enteric bacteria is the Rcs phosphorelay system (RcsCDB), which regulates numerous phenotypes such as exopolysaccharide production, swarming motility and bacterial virulence. Orphan genes (ORFans) are annotated genes that exclusively exist in a particular genome, strain, species or lineage. One of the enterobacteria-specific orphan genes is annotated as ybjN gene. So far, our knowledge about the function of ybjN gene is very limited. First, four wild-type strains (Ea1189, Ea273, Ea110, and CFBP1430), widely used in studies of E. amylovora pathogenesis, have been analyzed and compared to determine if there is a correlation between bacterial virulence and levels of virulence gene expression. Virulence tests on Golden Delicious apples and root stock plants revealed that American strains caused more severe disease than those caused by European strains. Further molecular analyses revealed that the ability to cause disease on apple leaves was positively correlated with the level of amylovoran production and T3SS gene expression. Second, systemic studies were carried out on the Rcs phosphorelay system and have revealed its essential roles in E. amylovora virulence and survival: 1) The Rcs phosphorelay was essential for bacterial virulence and amylovoran production; 2) Comparative characterization of RcsC sensor kinase showed that the sensor domain of RcsC was important for the regulation of bacterial virulence; 3) novel genes regulated by RcsB and RcsC were identified by microarray assays. Third, a conserved hypothetical gene amyR from E. amylovora and its homolog ybjN from E. coli were functionally characterized. AmyR negatively controlled bacterial virulence by regulating the expression of both amylovoran and T3SS genes in E. amylovora; whereas YbjN conveyed pleiotropic effects on stress responses and survival in E. coli. Furthermore, global gene expression profilings for amyR and ybjN in E. amylovora and E. coli were performed, respectively.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Wang, Dongping

Contributors dc:contributor

• Zhao, Youfu
• Korban, Schuyler S.
• Clough, Steven J.
• Caetano-Anollés, Gustavo

• Erwinia
• regulation
• two component signal transduction systems
• virulence

Statement dc:rights

• Copyright 2011 Dongping Wang

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/24468

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/24468