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Iron is a triggering factor for differential expression of Erwinia chrysanthemi strain 3937 pectate lyases in pathogenesis of African violets

Masclaux, C., Hugouvieux-Cotte-Pattat, N., Expert, D.
Molecular plant-microbe interactions 1996 v.9 no.3 pp. 198-205
Saintpaulia, gene expression, pectate lyase, recombinant DNA, reporter genes, beta-glucuronidase, pathogenesis, iron, structural genes, promoter regions, Saintpaulia ionantha, siderophores, histochemistry
This work was aimed at investigating possible links between pectinolysis and chrysobactin-dependent iron assimilation, two major determinants of the pathogenicity of Erwinia chrysanthemi 3937 on African violets. Transcriptional expression of the relevant pectinase-encoding genes (pelA to pelE and pem) was analyzed during the early stages of pathogenesis by means of GUS fusions. The pelD::uidA fusion was induced 6 h after inoculation, earlier and in higher levels than pelB::uidA, pelC::uidA, pelE::uidA, and pem::uidA; pelA::uidA was not induced. PelD::uidA expression was compared with that of pelE::uidA in different mutants. In a cbr mutant, derepressed for chrysobactin, pelD::uidA was weakly expressed, pelE::uidA expression did not change significantly, and production of the cognate PelD and PelE isoenzymes was reduced. A chrysobactin-deficient pelD::uidA mutant grew poorly; no pelD::uidA expression was recovered. In a kdgR mutant derepressed for pectinolytic functions, pelD::uidA expression was the same until 15 h postinoculation, after which a substantial increase was apparent. The expression of pelD::uidA was stimulated by the presence of iron chelators in the growth medium and the absence of functional chrysobactin-mediated iron uptake. The data provide evidence supporting the central role of iron in plant pathogenesis.