Xanthomonas campestris attenuates virulence by sensing light through a bacteriophytochrome photoreceptor

HERNÁN R. BONOMI; LAILA TOUM; GABRIELA SYCZ; RODRIGO SIEIRA; ANDRÉS M. TOSCANI; GUSTAVO E. GUDESBLAT; FEDERICO COLUCCIO LESCOW; FERNANDO A. GOLDBAUM; ADRIÁN A. VOJNOV; FLORENCIA MALAMUD

EMBO REPORTS

NATURE PUBLISHING GROUP

Lugar: Londres; Año: 2016 vol. 17 p. 1565 - 1577

1469-221X

Phytochromes constitute a major photoreceptor family found inplants, algae, fungi, and prokaryotes, including pathogens. Here,we report that Xanthomonas campestris pv. campestris (Xcc), thecausal agent of black rot disease which affects cruciferous cropsworldwide, codes for a functional bacteriophytochrome (XccBphP).XccBphP possesses an N-terminal PAS2-GAF-PHY photosensorydomain triad and a C-terminal PAS9 domain as its output module.Our results show that illumination of Xcc, prior to plant infection,attenuates its virulence in an XccBphP-dependent manner. Moreover,in response to light, XccBphP downregulates xanthanexopolysaccharide production and biofilm formation, two knownXcc virulence factors. Furthermore, the XccbphP null mutantshows enhanced virulence, similar to that of dark-adapted Xcccultures. Stomatal aperture regulation and callose deposition, bothwell-established plant defense mechanisms against bacterialpathogens, are overridden by the XccbphP strain. Additionally, anRNA-Seq analysis reveals that far-red light or XccBphP overexpressionproduces genomewide transcriptional changes, including theinhibition of several Xcc virulence systems. Our findings indicatethat Xcc senses light through XccBphP, eliciting bacterial virulenceattenuation via downregulation of bacterial virulence factors. Thecapacity of XccBphP to respond to light both in vitro and in vivowas abolished by a mutation on the conserved Cys13 residue.These results provide evidence for a novel bacteriophytochromefunction affecting an infectious process.