title: The Response regulator HrpY of Dickeya dadantii 3937 regulates virulence genes not linked to the hrp cluster.
abstract: HrpX/Y is a putative two-component system (TCS) encoded within the type III secretion system (T3SS) gene cluster of Dickeya dadantii. A linear regulatory cascade initiated by HrpX/Y that leads to activation of the downstream T3SS genes via HrpS and HrpL was described previously. Therefore, in D. dadantii, HrpX/Y plays an important role in regulation of genes involved in bacteria-plant interactions and bacterial aggregation via the T3SS. HrpX/Y is the only TCS shared among the plant-pathogenic enterobacteria that is not also present in animal-associated enterobacteria. To date, the genes known to be regulated by HrpY are restricted to the hrp and hrc genes and no signal has been identified that triggers HrpY-dependent gene expression. We demonstrated that HrpY interacts with the hrpS promoter in vitro. We then used a transposon-based system to isolate previously unidentified HrpY-dependent genes, including genes previously shown to affect virulence, including kdgM and acsC. HrpY is a dual regulator, positively regulating at least 10 genes in addition to those in the hrp gene cluster and negatively regulating at least 5 genes. The regulatory effect on one gene depended on the culture medium used. Of the 16 HrpY-regulated genes identified in this screen, 14 are not present in Pectobacterium atrosepticum, the nearest relative of D. dadantii with a sequenced genome. None of the newly identified HrpY-regulated genes were required for bacterial aggregation; thus, neither acyl-homoserine lactone-mediated quorum sensing nor the Rcs signal transduction system which regulates colanic acid, a molecule that plays an important role in biofilm formation in other enterobacteria, are required for D. dadantii aggregation.
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison 53706, USA.
authors.forename: Mee-Ngan
authors.initials: MN
authors.lastname: Yap
authors.forename: Ching-Hong
authors.initials: CH
authors.lastname: Yang
authors.forename: Amy O
authors.initials: AO
authors.lastname: Charkowski
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004755:Enterobacteriaceae / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity*; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D014157:Transcription Factors; D037521:Virulence Factors