Erwinia carotovora has two KdgR-like proteins belonging to the IcIR family of transcriptional regulators: identification and characterization of the RexZ activator and the KdgR repressor of pathogenesis

Abstract

A novel Erwinia carotovora subsp. carotovora mutant designated RexZ, begulator of Eoenzymes) showed reduced production of the degradative exoenzymes. The mxZ gene product shows similarity to the KdgR regulatory protein from fmvinia 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 Rex2 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 Em carotovora subsp. carotovora and E carotovora subsp. afroseptica share a high level of sequence identity with the KdgR homologues from E. chrysantherni 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 cetlular levet of Rex2 protein was unaffected by the presence of pectic compounds. This study shows that the complex regulatory network governing virulence in the erwinias involves two total ty distinct, but highly conserved, members of the IclR class of DNA binding proteins: RexZ and KdgR. INTRODUCTIONThe phytopathogenicity of several Erwinia species is correlated with the ability to produce and secrete plant cell wall degrading enzymes such as pectinases, cellulases (Cel) and proteases (Prt) (Collmer & Keen, 1986;Barras et al., 1994). The crucial role of these enzymes, particularly the pectate lyases (Pel), in the Abbreviations: CRP, cyclic AMP receptor protein; KDG, 2-keto-3-deoxygluconate; OHHL, N-(3-oxohexanoyt)-~-homoserine lactone; PGA, polygalacturonate.The GenBank accession numbers for the sequences reported in this paper are given in the text.virulence of soft-rot Erwinia has been confirmed by the isolation of mutants exhibiting reduced virulence that are defective for production or secretion of these enzymes (Boccara et al., 1988;Hinton et al., 1989; Pirhonen st al., 1991). Exoenzyme production by softrot Erwinia species responds to several environmental conditions (Hugouvieux-Cotte-Pattat et af., 1996) ; presence of pectin-degradative products or plant extract, anaerobiosis, temperature, nitrogen starvation, osmolarity, catabolite repression, iron availability and growth phase.In Erwinia chrysanthemi 3937, attention has been focused on the pectin degradation pathway, and the different steps of this metabolic pathway have been characterized. The degradation of the pectic compounds is initiated by extracellular pectinases, including two pectin methylesterases (encoded by pernA and pemB) (Laurent et al., 1993;Shevchik et al., 1996), five major isoenzymes of pectate lyases (encoded by pelA, pel& pelC, pelD and pelE) and a set of secondary pectate lyases which generate u...

Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

“…A KdgR homolog, RexZ, has also been identified and characterized in E. carotovora. Unlike KdgR, RexZ is an activator of exoenzyme production (483). RexZ orthologs were also identified in all species of Erwinia tested, including E. chysanthemi EC16 and 3937, E. carotovora subsp.…”

“…Studies of KdgR have been done mostly with E. chrysanthemi, but E. carotovora KdgR has been shown to act similarly (313,483). A KdgR homolog, RexZ, has also been identified and characterized in E. carotovora.…”

Elevated Temperature Enhances Virulence ofErwinia carotovorasubsp.carotovoraStrain EC153 to Plants and Stimulates Production of the Quorum Sensing Signal,N-Acyl Homoserine Lactone, and Extracellular Proteins

“…carotovora uses the type III secretion system to produce effector proteins, including harpin, that determine the outcomes of bacterial interactions with certain plant hosts (1,5,19,28,39). Genetic and physiological data indicate that production of these enzymes and effector proteins is coregulated by the quorumsensing signal AHL (reference 52 and references therein), plant signals (7, 33), and various transcriptional factors (9,11,12,13,16,24,25,30,31,42,47). In addition, extracellular protein/enzyme production is also subject to posttranscriptional regulation by RsmA, an RNA binding protein, and rsmB RNA (Rsm is the regulator of secondary metabolites) (6, 10,…”

KdgR, an IClR Family Transcriptional Regulator, Inhibits Virulence Mainly by Repression of hrp Genes in Xanthomonas oryzae pv. oryzae

“…Erwinia chrysanthemi 3937) (28,29,40,42,43,48). In vitro analysis demonstrated that KdgR binds directly to the promoter regions of the in vivo-controlled genes (51). KdgR was also found in other plant-pathogenic enterobacteria: Erwinia carotovora (syn.…”

“…KdgR was also found in other plant-pathogenic enterobacteria: Erwinia carotovora (syn. Pectobacterium carotovorum) and Erwinia amylovora (28,51). Furthermore, KdgR was reported to have a wider range of targets, and its role may not be restricted to pectinolysis (15,23).…”