The full-length bacteriophytochrome from the plant pathogen Xanthomonas campestris: insights into its struture and function

OTERO LH; VELÁZQUEZ-ESCOBAR F; GUDESBLAT G; HILDEBRANDT P; BONOMI HR; MALAMUD F; TOUM L; TOSCANI AM; MROGINSKI MA; GOLDBAUM FA; KLINKE S; FERNÁNDEZ LÓPEZ M; COLUCCIO LESKOW F; VOJNOV AA

Galveston, Texas

Conferencia; Photosensory Receptors & Signal Transduction; 2016

Gordon Research Conference

Phytochromes constitute a major superfamily of light-sensing proteins that are reversibly photoconverted between a red-absorbing (Pr) and a far-red-absorbing (Pfr) state. These photorecepetors are found in plants, algae, fungi, and prokaryotes, 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 a functional bacteriophytochrome (XccBphP). To date, although several BphPs have been biophysically characterized in detail, it is not fully understood yet how structural changes are propagated from the photosensory module to the output module during the signal transduction event. Additionally, most biological bacteriophytochrome functions remain elusive. Here we present the crystal structure of the full-length XccBphP bearing its photosensor (PAS2-GAF-PHY domain triad) and its complete output module, a PAS9 domain. Spectroscopic and theoretical calculations on XccBphP were performed to elucidate its photocycle and chromophore configuration. Moreover, our findings show that in vivo Xcc senses light through XccBphP, eliciting bacterial virulence attenuation via down-regulation of bacterial virulence factors. This work contributes to understand the light-induced structural changes propagated from the photosensor to the output modules in phytochrome signaling and provide evidence for a novel bacteriophytochrome function affecting an infectious process.