title: Global regulatory networks control the hrp regulon of the gall-forming bacterium Pantoea agglomerans pv. gypsophilae.
abstract: Gall formation by Pantoea agglomerans pv. gypsophilae is dependent on the hypersensitive response and pathogenicity (hrp) system. Previous studies demonstrated that PagR and PagI, regulators of the quorum-sensing system, induce expression of the hrp regulatory cascade (i.e., hrpXY, hrpS, and hrpL) that activates the HrpL regulon. Here, we isolated the genes of the Gac/Rsm global regulatory pathway (i.e., gacS, gacA, rsmB, and csrD) and of the post-transcriptional regulator rsmA. Our results demonstrate that PagR and PagI also upregulate expression of the Gac/Rsm pathway. PagR acts as a transcriptional activator of each of the hrp regulatory genes and gacA in a N-butanoyl-L-homoserine lactone-dependent manner as shown by gel shift experiments. Mutants of the Gac/Rsm genes or overexpression of rsmA significantly reduced Pantoea agglomerans virulence and colonization of gypsophila. Overexpression of rsmB sRNA abolished gall formation, colonization, and hypersensitive reaction on nonhost plants and prevented transcription of the hrp regulatory cascade, indicating a lack of functional type III secretion system. Expression of rsmB sRNA in the background of the csrD null mutant suggests that CsrD may act as a safeguard for preventing excessive production of rsmB sRNA. Results presented indicate that the hrp regulatory cascade is controlled directly by PagR and indirectly by RsmA, whereas deficiency in RsmA activity is epistatic to PagR induction.
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Tel-Aviv University, Tel-Aviv, Israel.
authors.forename: Mary
authors.initials: M
authors.lastname: Panijel
authors.forename: Laura
authors.initials: L
authors.lastname: Chalupowicz
authors.forename: Guido
authors.initials: G
authors.lastname: Sessa
authors.forename: Shulamit
authors.initials: S
authors.lastname: Manulis-Sasson
authors.forename: Isaac
authors.initials: I
authors.lastname: Barash
mesh_terms: D015107:4-Butyrolactone / Q000031:analogs & derivatives; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D029748:Caryophyllaceae / Q000382:microbiology; D024202:Electrophoretic Mobility Shift Assay; D015964:Gene Expression Regulation, Bacterial; D053263:Gene Regulatory Networks; D054884:Host-Pathogen Interactions; D008958:Models, Molecular; D009154:Mutation; D020636:Pantoea / Q000235:genetics* / Q000472:pathogenicity* / Q000502:physiology; D018515:Plant Leaves / Q000382:microbiology; D010941:Plant Tumors / Q000382:microbiology*; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D053038:Quorum Sensing / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics; D018085:Regulon; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D015533:Transcriptional Activation; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; C092312:N-butyrylhomoserine lactone; D012329:RNA, Bacterial; D014157:Transcription Factors; D015107:4-Butyrolactone