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 C. LESKOW; FERNANDO A. GOLDBAUM; ADRIÁN A. VOJNOV; FLORENCIA MALAMUD

EMBO REPORTS

NATURE PUBLISHING GROUP

Lugar: Londres; Año: 2016

1469-221X

p { margin-bottom: 0.1in; direction: ltr; line-height: 120%; text-align: justify; }p.western { font-family: "Times New Roman",serif; font-size: 11pt; }p.cjk { font-size: 11pt; }p.ctl { font-size: 11pt; }a:link { color: rgb(0, 0, 255); }Phytochromes constitute a major photoreceptor family found in plants,algae, fungi, and prokaryotes, including pathogens. Here we reportthat Xanthomonas campestris pv. campestris (Xcc),the causal agent of black rot disease which affects cruciferous cropsworldwide, codes for a functional bacteriophytochrome (XccBphP).XccBphP possesses an N-terminal PAS-GAF-PHY photosensorydomain triad and a C-terminal PAS9 domain as its output module. Ourfindings show that illumination of Xcc, prior to plantinfection, attenuates its virulence in an XccBphP-dependentmanner. Moreover, in response to light, XccBphP down-regulatesxanthan exopolysaccharide production and biofilm formation, two knownXcc virulence factors. Furthermore, the XccbphPnull-mutant shows enhanced virulence, similar to that of dark-adaptedXcc cultures. Stomatal aperture regulation and callosedeposition, both well-established plant defense mechanisms againstbacterial pathogens, are overridden by the XccbphP strain.Also, an RNA-Seq analysis reveals that far-redlight or XccBphPoverexpression produces genome-wide transcriptional changes,including the inhibition of several Xccvirulence systems. Ourfindings show that Xcc senses light through XccBphP,eliciting bacterial virulence attenuation via down-regulationof bacterial virulence factors. To finish, by amutational approach on the conserved Cys13 residue we could abolishedthe capacity of XccBphPto respond to light both in vitroand in vivo. The resultspresented in this work provide evidence for a novelbacteriophytochrome function affecting an infectious process.