Iron Is a Triggering Factor for Differential Expression of Erwinia chrysanthemi Strain 3937 Pectate Lyases in Pathogenesis of African Violets. Celine Masclaux. Laboratoire de Pathologie Vegetale, INA P-G / INRA, 16 rue Claude Bernard, F-75 231 Paris, France. Nicole Hugouvieux-Cotte-Pattat(2), and Dominique Expert(1). (1)Laboratoire de Pathologie Vegetale, INA P-G / INRA, 16 rue Claude Bernard, F-75 231 Paris, France; (2) Laboratoire de Genetique Moleculaire des Microorganismes, URA CNRS 1486, Biochimie 406, INSA de Lyon, 20 Avenue Albert Einstein, 69 621 Villeurbanne, France. MPMI 9:198-205. Accepted 21 December 1995, This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1996.

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 pern) 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, pelEr.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; nopelD::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.