Chapter 19
Methods to Study Quorum Sensing-Dependent Virulence
and Movement of Phytopathogens In Planta
Shulamit Manulis-Sasson and Laura Chalupowicz
Abstract
Cell-to-cell communication mediated by the diffusible signal factor (DSF) is a common form of gene
regulation and plays an important role in virulence of many plant pathogenic bacteria includingXantho-
monasspp. Here we describe several approaches to study the involvement of DSF-dependent QS system of
the plant pathogenic bacteriaXanthomonas campestrispv.pelargonii(Xhp) as an example of theXantho-
monasspp. The methods described include detection and measurement of DSF, movement in planta,
colonization, and aggregate formation.
Key wordsDSF,Xanthomonas campestris, GFP, Quorum sensing, Plant pathogen,rpfF,rpfC1 Introduction
The Quorum Sensing (QS) system plays a significant role in viru-
lence of plant pathogenic bacteria. Two major classes of QS-signals
used by Gram-negative bacteria are acylated homoserine lactones
(AHLs) and diffusible signal factor (DSF) composed ofα,β-unsat-
urated fatty acids [1–3]. DSFs act as the main QS signal inXantho-
monasspp. and in other genera of the Xanthomonadaceae family
likeXylella fastidiosaandStenotrophomonasspp., and are found
together with AHLs in bacteria belonging to other families such
asBurkholderia cenocepaciaorPseudomonas aeruginosa[4]. Several
species and pathovars of Xanthomonas contain the cluster of
pathogenicity-associated genes designated as rpf(regulation of
pathogenicity factors) [4] (Fig.1). InXanthomonas campestrispv.
campestrisDSF, which is cis-11-methyl-2-dodecenoic acid (Fig.2)
[5], is synthetized by RpfF [1, 6]. The DSF sensing mechanism
involves RpfC, which encodes the histidine sensor kinase of the
two-component system RpFC/RpfG.
Genetic and gene expression analyses showed that the DSF
QS-signaling pathway regulates diverse biological functions related
to virulence, including biosynthesis of polysaccharides (xanthan),Livia Leoni and Giordano Rampioni (eds.),Quorum Sensing: Methods and Protocols, Methods in Molecular Biology,
vol. 1673,https://doi.org/10.1007/978-1-4939-7309-5_19,©Springer Science+Business Media LLC 2018
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