Open AccessA novel transcriptional autoregulatory loop enhances expression of the Pantoea stewartii subsp. stewartii Hrp type III secretion system
Author(s) -
Merighi Massimo,
Majerczak] Doris R.,
Coplin David L.
Publication year - 2005
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1016/j.femsle.2005.01.009
Subject(s) - regulon , pantoea , biology , sigma factor , operon , type three secretion system , genetics , transcription (linguistics) , gene , promoter , regulation of gene expression , gene expression , mutant , linguistics , philosophy , 16s ribosomal rna
The hrp type III secretion regulon of Pantoea stewartii is regulated by a cascade involving the HrpX/HrpY two‐component system, the HrpS enhancer‐binding protein and the HrpL alternate sigma factor. hrpXY is both constitutive and autoregulated; HrpY controls hrpS ; and HrpS activates hrpL . These regulatory genes are arranged in the order hrpL , hrpXY and hrpS and constitute three operons. This study describes a novel autoregulatory loop involving HrpS. Genetic experiments using a chromosomal hrpS ‐ lacZ fusion demonstrated that ectopic expression of HrpS increases hrpS transcription and that this effect is blocked by polar mutations in hrpXY and hrpL and by a nonpolar mutation in hrpY . RT‐PCR and Northern blot analysis revealed a hrpL ‐ hrpXY polycistronic mRNA. These results suggest that HrpS‐mediated autoregulation is due to activation of hrpS by increased levels of HrpY resulting from read‐through transcription of hrpXY from the hrpL promoter. This novel autoregulatory loop may serve to rapidly induce hrp genes during infection and to compensate for negative regulatory mechanisms that keep the regulon off in the insect vector.