Estructura y función del bacteriofitocromo del fitopatógeno Xanthomonas campestris

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

San Miguel de Tucumán

Conferencia; III Reunión de Fotobiólogos Moleculares Argentinos; 2016

GRAFOB

Phytochromes constitute a major superfamily of light-sensing proteins that are reversibly photoconvertedbetween a red-absorbing (Pr) and a far-red-absorbing (Pfr) state. Bacteriophytochromes (BphPs) are foundamong photosynthetic and non-photosynthetic bacteria, including pathogens. To date, several BphPs have beenbiophysically characterized. However, it is still not fully understood how structural changes are propagated fromthe photosensory module to the output module during the signal transduction event. We have solved the crystalstructure of the full-length BphP from the plant pathogen Xanthomonas campestris pv. campestris (XccBphP)bearing its photosensor and its complete output module, a PAS9 domain [1]. In the crystals, the protein wasfound to be in the Pr state whereas diffraction data together with resonance Raman spectroscopic and theoreticalresults indicate a ZZZssa and a ZZEssa chromophore configuration corresponding to a mixture of Pr and MetaRstate, the precursor of Pfr. The XccBphP quaternary assembly reveals a head-to-head dimer in which theoutput module contributes to the helical dimer interface. The photosensor, which is shown to be a bathy-likeBphP, is influenced in its dark reactions by the output module. Our structural analyses suggest that thephotoconversion between the Pr and Pfr states in the full-length XccBphP may involve changes in the relativepositioning of the output module.We then tested the hypothesis that XccBphP plays a role in bacterial pathogenesis. Our findings, show thatillumination of X. campestris, prior to plant infection, attenuates bacterial virulence in an XccBphP-dependentmanner. In response to light, XccBphP down-regulates xanthan exopolysaccharide production and biofilmformation, two known Xcc virulence factors. Furthermore, the XccbphP null-mutant shows enhanced virulence,similar to that of dark-adapted Xcc cultures. Stomatal aperture regulation and callose deposition, both wellestablishedplant defense mechanisms against bacterial pathogens, are overridden by the XccbphP strain.Additionally, an RNA-Seq analysis reveals that far-red light or XccBphP overexpression produce genome-widetranscriptional changes, including the inhibition of several Xcc virulence systems. Our findings show that Xccsenses light through 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 was abolished by amutation on the conserved Cys13 residue.Referencias1- Otero LH, Klinke S, Rinaldi J, Velázquez-Escobar F, Mroginski MA, Fernández López M, Malamud F, VojnovAA, Hildebrandt P, Goldbaum FA, Bonomi HR. J Mol Biol. 2016. doi: 10.1016/j.jmb.2016.04.012