Affiliation:
1. Laboratoire Interactions Plantes-Microorganismes, CNRS-INRA, UMR2594, BP27, 31326 Castanet-Tolosan, France
Abstract
ABSTRACT
The ability of
Ralstonia solanacearum
to cause disease on plants depends on its type III secretion system (TTSS) encoded by
hrp
genes. The expression of
hrp
genes and known TTSS substrates is coordinately regulated by HrpB, a member of the AraC family of transcriptional regulators. Two HrpB-regulated promoters (
hrpY
and
popABC
) were characterized by deletion analysis, and the HrpB-dependent activation of these promoters was found to be conferred by a 25-nucleotide DNA element, the
hrp
II
box (TTCGn16TTCG), which is present in other
hrp
promoters. The
hrp
II
box element is an imperfect plant inducible promoter box, an element which was originally found in
hrp
promoters of
Xanthomonas campestris
(S. Fenselau and U. Bonas, Mol. Plant-Microbe Interact. 8:845-854, 1995) but which was not characterized at the molecular level. Site-directed mutagenesis showed that the
hrp
II
box is essential for
hrpY
promoter activation in vivo. Functional analysis of the
hrp
II
box element identified critical parameters that are required for HrpB-dependent activity. Further mapping analyses of several other
hrpB
-dependent promoters also indicated that the position of the
hrp
II
box is conserved, at −70 to −47 bp from the transcriptional start. As a first step toward identifying novel TTSS effectors, we used the
hrp
II
box consensus sequence to search for potential HrpB-regulated promoters in the complete genome sequence of
R. solanacearum
strain GMI1000. Among the 114 genes identified, a subset of promoters was found to have a structural relationship with
hrp
promoters, thus providing a pool of candidate genes encoding TTSS effectors.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
102 articles.
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