Diffusible Signal Factor (DSF) Synthase RpfF of Xylella fastidiosa Is a Multifunction Protein Also Required for Response to DSF

Xylella fastidiosa, like related Xanthomonas species, employs an Rpf cell-cell communication system consisting of a diffusible signal factor (DSF) synthase, RpfF, and a DSF sensor, RpfC, to coordinate expression of virulence genes. While phenotypes of a ΔrpfF strain in Xanthomonas campestris could b...

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Bibliographic Details
Published in:Journal of Bacteriology 2013-12, Vol.195 (23), p.5273-5284
Main Authors: Ionescu, Michael, Baccari, Clelia, Da Silva, Aline Maria, Garcia, Angelica, Yokota, Kenji, Lindow, Steven E
Format: Article
Language:English
Subjects:
active sites
alanine
Bacteria
Bacterial Proteins - genetics
Bacterial Proteins - metabolism
Bacteriology
cell communication
Cells
Gene expression
Gene Expression Regulation, Bacterial - physiology
genes
Genotype & phenotype
glutamic acid
grapes
Molecules
mutants
Mutation
phenotype
Plant Diseases - microbiology
Proteins
quorum sensing
virulence
Vitis - microbiology
Xanthomonas campestris
Xylella - genetics
Xylella - metabolism
Xylella - pathogenicity
Xylella fastidiosa
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Summary:Xylella fastidiosa, like related Xanthomonas species, employs an Rpf cell-cell communication system consisting of a diffusible signal factor (DSF) synthase, RpfF, and a DSF sensor, RpfC, to coordinate expression of virulence genes. While phenotypes of a ΔrpfF strain in Xanthomonas campestris could be complemented by its own DSF, the DSF produced by X. fastidiosa (XfDSF) did not restore expression of the XfDSF-dependent genes hxfA and hxfB to a ΔrpfF strain of X. fastidiosa, suggesting that RpfF is involved in XfDSF sensing or XfDSF-dependent signaling. To test this conjecture, rpfC and rpfF of X. campestris were replaced by those of X. fastidiosa, and the contribution of each gene to the induction of a X. campestris DSF-dependent gene was assessed. As in X. fastidiosa, XfDSF-dependent signaling required both X. fastidiosa proteins RpfF and RpfC. RpfF repressed RpfC signaling activity, which in turn was derepressed by XfDSF. A mutated X. fastidiosa RpfF protein with two substitutions of glutamate to alanine in its active site was incapable of XfDSF production yet enabled a response to XfDSF, indicating that XfDSF production and the response to XfDSF are two separate functions in which RpfF is involved. This mutant was also hypervirulent to grape, demonstrating the antivirulence effects of XfDSF itself in X. fastidiosa. The Rpf system of X. fastidiosa is thus a novel example of a quorum-sensing signal synthase that is also involved in the response to the signal molecule that it synthesizes.
ISSN:0021-9193
1098-5530
1067-8832
DOI:10.1128/JB.00713-13