The AmyR regulon in Erwinia amylovora

Microarray analysis was used to identify genes that were controlled by AmyR in minimal and on immature pear fruits. Consistent with amylovoran production, an inverse correlation was observed between amyR expression and the expression level of amylovoran biosynthetic genes in liquid media. Interestingly, over-expression of AmyR suppressed the expression of type III secretion system genes including hrpA, hrpN and dspEF after pear fruit infection. Consistent with levan production and swarming motility, levasucrase and flagellar genes were both down-regulated both in the amyR mutant and over-expression strains in liquid media. Together, our results suggest that AmyR plays an important role in regulating bacterial exopolysaccharide production and virulence in E. amylovora. A total of 14 samples were analyzed in two conditions: For the in vitro condition (MBMA medium + 1% sorbitol), Erwinia amylovora wild type strain (2 replicates); E. amylovora amyR mutant strain (3 replicates); E. amylovora amyR over-expression strain (3 replicates); For the in vivo condition (on wounded immature pear fruits), Erwinia amylovora wild type strain (2 replicates); E. amylovora amyR mutant strain (2 replicates); E. amylovora amyR over-expression strain (2 replicates).