Virulence and in planta movement of Xanthomonas hortorum pv. pelargonii are affected by the diffusible signal factor (DSF)‐dependent quorum sensing system. (29th January 2015)

• Record Type: Journal Article
• Authors: Barel, Victoria; Chalupowicz, Laura; Barash, Isaac; Sharabani, Galit; Reuven, Michal; Dror, Orit; Burdman, Saul; Manulis‐Sasson, Shulamit
• Is Part Of: Molecular plant pathology. Volume 16:Number 7(2015:Sep.)
• Page Start: 710
• Page End: 723
• Publication Date: 2015-01-29
• Subjects: Plant diseases -- Molecular aspects -- Periodicals; Plant-pathogen relationships -- Molecular aspects -- Periodicals; 571.936
• DOI: 10.1111/mpp.12230
• Languages: English
• ISSNs: 1464-6722

Abstract

<abstract abstract-type="main"> <title>Summary</title> <p> <italic>Xanthomonas hortorum</italic> pv. <italic>pelargonii</italic> (<italic>Xhp</italic>), 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 <italic>Xhp</italic>, we have disrupted the quorum sensing (QS) genes, which mediate the biosynthesis and sensing of the diffusible signal factor (DSF). Mutations in <italic>rpfF</italic> (encoding the DSF synthase) and <italic>rpfC</italic> (encoding the histidine sensor kinase of the two‐component system RfpC/RpfG) and overexpression of <italic>rpfF</italic> showed a significant reduction in incidence and severity of the disease on pelargonium<italic>.</italic> 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 <italic>rpfF</italic> and <italic>rpfC</italic> knockout mutants, as well as the <italic>rpfF</italic>‐overexpressing strain, remained confined to the vicinity of the inoculation site. The <italic>rpfF</italic> and <italic>rpfC</italic> 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 <italic>in vitro</italic> conditions, whereas the wild‐type strain formed microcolonies. Expression levels of putative virulence genes <italic>in planta</italic> 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 <italic>Xhp</italic> in pelargonium.</p> </abstract>