Xanthomonas campestris attenuates virulence by sensing light through a bacteriophytochrome photoreceptor

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

EMBO REPORTS

NATURE PUBLISHING GROUP

Lugar: Heidelberg; Año: 2016

1469-221X

AbstractPhytochromes constitute a major photoreceptor family found in plants, algae, fungi, andprokaryotes, including pathogens. Here we report that Xanthomonas campestris pv. campestris(Xcc), the causal agent of black rot disease which affects cruciferous crops worldwide, codes for afunctional bacteriophytochrome (XccBphP). XccBphP possesses an N-terminal PAS2-GAF-PHYphotosensory domain triad and a C-terminal PAS9 domain as its output module. Our findings showthat illumination of Xcc, prior to plant infection, attenuates its virulence in an XccBphP-dependentmanner. Moreover, in response to light, XccBphP down-regulates xanthan exopolysaccharideproduction and biofilm formation, two known Xcc virulence factors. Furthermore, the XccbphPnull-mutant shows enhanced virulence, similar to that of dark-adapted Xcc cultures. Stomatalaperture regulation and callose deposition, both well-established plant defense mechanisms againstbacterial pathogens, are overridden by the XccbphP strain. Additionally, an RNA-Seq analysisreveals that far-red light or XccBphP overexpression produce genome-wide transcriptional changes,including the inhibition of several Xcc virulence systems. Our findings show that Xcc senses lightthrough XccBphP, eliciting bacterial virulence attenuation via down-regulation of bacterialvirulence factors. The capacity of XccBphP to respond to light both in vitro and in vivo wasabolished by a mutation on the conserved Cys13 residue. These results provide evidence for a novelbacteriophytochrome function affecting an infectious process.