Phytopathogenic bacteria of the species Pseudomonas, Erwinia and Xanthomonas contain a complex regulatory
network which belongs to the hrp genes (hypersensitive response and pathogenicity) and controls processes
involved in pathogenicity and induction of resistance responses in plants. In Pseudomonas syringae the hrp
regulatory cascade consists of three genes, hrpS, hrpR and hrpL. hrpL encodes an alternate sigma factor, which
recognizes the hrp-box, a sequence found upstream of many target genes of the regulatory cascade in
Pseudomonas. The two genes hrpS and hrpR are highly homologous and control the expression of hrpL. They
belong to the well conserved, enhancer-binding protein (EBP) family. EBPs function together with the alternate
sigma factor E-sigma 54 which recognizes promoters of the -12/-24 type.
Structurally, the EBPs are characterized by a central activator domain and the C-terminal domain, containing a
DNA binding helix-turn-helix motif. Despite the structural and sequence similarities between hrpR and hrpS, the
two genes have different specificities and function at different positions of the hrp regulation cascade.
1n this project it is proposed to analyse the different domains of the two regulatory proteins and to characterize the
specificity determinants, which constitute the basis for the functional differences between hrpR and hrpS, by
mutagenesis and domain switching analysis.