Impaired induction and self-catabolite repression of extracellular pectate lyase in Erwinia chrysanthemi mutants deficient in oligogalacturonide lyase

Abstract

The pectate lyase (PL; EC 4.2.2.2) secreted by the plant pathogen Erwinia chrysanthemi is induced and catabolite repressed by different concentrations of its own product, digalacturonic acid 4,5-unsaturated at the nonreducing end [u(GalUA) 2 ]. Both activities of u(GalUA) 2 depend on its cleavage by oligogalacturonide lyase (OGL; EC 4.2.2.6). This intracellular enzyme converts u(GalUA) 2 to the deoxyketuronic acid 4-deoxy-L- threo -5-hexosulose uronic acid, which is then isomerized to 3-deoxy-D- glycero -2,5-hexodiulosonic acid. An OGL-deficient mutant unable to grow on u(GalUA) 2 was poorly induced by u(GalUA) 2 or by D-galacturonan but produced wild-type levels of PL when supplied with 3-deoxy-D- glycero -2,5-hexodiulosonic acid. PL synthesis in the mutant could also be stimulated by 4,5-unsaturated trigalacturonic acid, from which deoxyketuronic acid is released by another intracellular enzyme. An OGL-deficient mutant that grew slowly on u(GalUA) 2 in comparison with the wild-type parent was hyperinduced by u(GalUA) 2 unless catabolite repression was relieved by cyclic AMP or imposed by logarithmic growth on glycerol. PL synthesis is also stimulated by saturated digalacturonic acid, which is released from D-galacturonan by another extracellular enzyme, exo-poly-α-D-galacturonosidase (EC 3.2.1.82). Because these dimers stimulate PL synthesis at concentrations (wt/vol) 1/1000th of the concentration required by D-galacturonan, and because an OGL-deficient mutant uninducible by dimers was also uninducible by D-galacturonan, we postulate that PL induction by pectic polymers entails extracellular formation of dimers and subsequent intracellular conversion to deoxyketuronic acids, the apparent inducers of PL.

Molecular cloning, nucleotide sequence, and marker exchange mutagenesis of the exo-poly-alpha-D-galacturonosidase-encoding pehX gene of Erwinia chrysanthemi EC16

“…Pectate lyase induction appears to be an autocatalytic process in which extracellular degradation of the substrate by basal levels of secreted pectic enzymes results in the release of assimilable oligogalacturonates, which signal the presence of the polymer (6,7). The induction of pectate lyase by the Peh-mutant CUCPB5008 was significantly reduced relative to the wild type.…”

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

“…These mutants are also unable to grow on pectin or PGA as the sole carbon sources (402). Expression of pectinase genes (pemA, pelB, pelC, pelD, and pelE) and of genes of the intracellular part of the pectin degradation pathway (ogl, kdul, and kdgT) is dramatically reduced in crp mutants (84). Similarly, an E. carotovora cya mutant (defective in cAMP production) is defective in Pel synthesis (336).…”

“…Early physiological studies suggested that pectinase production in Erwinia species is subject to catabolite repression (221). Catabolite repression was observed during growth in the presence of glucose and also in the presence of pectin catabolic products (84,491). The cyclic AMP (cAMP) receptor protein (CRP) is essential for this regulation ( Fig.…”

“…Expression of these genes is also inducible by demethylated derivatives, of pectin, polygalactoronate (PGA), or the monomer galacturonate. The analysis of mutants that are deficient in each step of the pectinolytic pathway allowed the identification of the true intracellular inducers, namely, KDG (2-keto-3-deoxygluconate), DKI (5-keto-4-deoxyuronate), and DKII (2,5-diketo-3-deoxygluconate (74,84,88,226,405). These compounds are the breakdown products of the long-chain pectate polymers, presumably generated by the basal level of pectate lyases (490).…”

2-keto-3-deoxygluconate transport system in Erwinia chrysanthemi

“…Pectin degradation by the phytopathogenic enterobacterium Erwinia chrysanthemi has been extensively studied (20 5-Keto-4-deoxyuronate (DKI) is the primary product formed by the catabolism of polygalacturonate by the pectate lyases and oligogalacturonate lyase (6,17,18) (Fig. 1).…”