title: Virulence and in planta movement of Xanthomonas hortorum pv. pelargonii are affected by the diffusible signal factor (DSF)-dependent quorum sensing system.
abstract: Xanthomonas hortorum pv. pelargonii (Xhp), the causal agent of bacterial blight in pelargonium, is the most threatening bacterial disease of this ornamental worldwide. To gain an insight into the regulation of virulence in Xhp, we have disrupted the quorum sensing (QS) genes, which mediate the biosynthesis and sensing of the diffusible signal factor (DSF). Mutations in rpfF (encoding the DSF synthase) and rpfC (encoding the histidine sensor kinase of the two-component system RfpC/RpfG) and overexpression of rpfF showed a significant reduction in incidence and severity of the disease on pelargonium. Confocal laser scanning microscopy images of inoculated plants with a green fluorescent protein (GFP)-labelled wild-type strain showed that the pathogen is homogeneously dispersed in the lumen of xylem vessels, reaching the apex and invading the intercellular spaces of the leaf mesophyll tissue within 21 days. In contrast, the rpfF and rpfC knockout mutants, as well as the rpfF-overexpressing strain, remained confined to the vicinity of the inoculation site. The rpfF and rpfC mutants formed large incoherent aggregates in the xylem vessels that might interfere with upward movement of the bacterium within the plant. Both mutants also formed extended aggregates under in vitro conditions, whereas the wild-type strain formed microcolonies. Expression levels of putative virulence genes in planta were substantially reduced within 48 h after inoculation with the QS mutants when compared with the wild-type. The results presented indicate that an optimal DSF concentration is crucial for successful colonization and virulence of Xhp in pelargonium.
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.|Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Victoria
authors.initials: V
authors.lastname: Barel
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Laura
authors.initials: L
authors.lastname: Chalupowicz
authors.affiliation: Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, 61390, Israel.
authors.forename: Isaac
authors.initials: I
authors.lastname: Barash
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Galit
authors.initials: G
authors.lastname: Sharabani
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Michal
authors.initials: M
authors.lastname: Reuven
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Orit
authors.initials: O
authors.lastname: Dror
authors.affiliation: Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, 76100, Israel.
authors.forename: Saul
authors.initials: S
authors.lastname: Burdman
authors.affiliation: Department of Plant Pathology and Weed Research, Agricultural Research Organization, The Volcani Center, Bet Dagan, 50250, Israel.
authors.forename: Shulamit
authors.initials: S
authors.lastname: Manulis-Sasson
mesh_terms: D018613:Microscopy, Confocal; D009154:Mutation; D053038:Quorum Sensing / Q000235:genetics*; D014774:Virulence; D014974:Xanthomonas / Q000502:physiology*
keywords: DSF; Pelargonium hortorum; aggregate formation; rpfC; rpfF