Summary auto-generated
This study identified and characterized two KdgR-like regulatory proteins in Erwinia carotovora, both belonging to the IclR family of transcriptional regulators. The researchers discovered RexZ, a novel regulator that acts as an activator of exoenzyme production (pectate lyases, cellulases, and proteases) essential for bacterial virulence in soft-rot disease. Unlike the KdgR repressor in E. chrysanthemi, RexZ functions as an activator. The rexZ gene was regulated by the cAMP-CRP complex in vitro. Additionally, the authors identified a second KdgR homologue in E. carotovora, distinct from RexZ, that was present across all tested Erwinia species. Both proteins share high sequence identity with KdgR homologues from E. chrysanthemi and E. coli. A rexZ mutant showed significantly reduced production of virulence-associated exoenzymes—cellulase and protease production decreased by 86% and 63% respectively, and pectate lyase activity was reduced fourfold. The study demonstrates that E. carotovora's virulence regulation involves two distinct but highly conserved IclR family proteins with opposing regulatory roles.
Key findings
- E. carotovora contains two KdgR-like proteins: RexZ (an activator) and a separate KdgR homologue (repressor), both IclR family members
- RexZ mutants showed dramatically reduced exoenzyme production, with cellulase reduced 86%, protease 63%, and pectate lyase activity reduced fourfold
- RexZ synthesis is controlled by the cAMP-CRP complex and RexZ levels are not affected by pectic compounds, unlike the classical KdgR repressor
- Both E. carotovora KdgR and RexZ proteins share high sequence identity with E. chrysanthemi and E. coli homologues across multiple Erwinia species
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Abstract
A novel Erwinia carotovora subsp. carotovora mutant designated RexZ, (regulator of exoenzymes) showed reduced production of the degradative exoenzymes. The rexZ gene product shows similarity to the KdgR regulatory protein from Erwinia chrysanthemi, described as the major repressor of the pectin catabolism pathway genes in the latter species. In vitro DNA--protein interaction experiments demonstrated that the synthesis of the RexZ protein is controlled by the cAMP--CRP (cAMP--receptor protein) complex. Western blot analysis also revealed the presence of a second KdgR homologue (distinct from RexZ) which, like RexZ, was present in all species of the genus Erwinia tested. The corresponding KdgR proteins from both E. carotovora subsp. carotovora and E. carotovora subsp. atroseptica share a high level of sequence identity with the KdgR homologues from E. chrysanthemi and Escherichia coli. Although the E. carotovora subsp. carotovora rexZ regulatory region displayed specific interactions with both the purified E. chrysanthemi KdgR repressor and the partially purified E. carotovora subsp. carotovora KdgR, in vivo quantification revealed that the cellular level of RexZ protein was unaffected by the presence of pectic compounds. This study shows that the complex regulatory network governing virulence in the erwinias involves two totally distinct, but highly conserved, members of the IclR class of DNA binding proteins: RexZ and KdgR.