In this communication, we examine the fate of iron during soft rot pathogenesis caused by Erwinia chrysanthemi on its host, Saintpaulia ionantha. l h e spread of soft rot caused by this enterobacterium was previously shown to depend on a functional genetic locus encoding a high-affinity iron assimilation system involving the catechol-type siderophore chrysobactin. Leaf intercellular fluid from healthy plants was analyzed with regard to the iron content and its availability for bacterial growth. It was compared to the fluid from diseased plants for the presence of strong iron ligands, using a new approach based on the iron-binding property of an ion-exchange resin. Further characterization allowed the identification of chrysobactin in diseased tissues, thus providing the first evidence for the externa1 release of a microbial siderophore during pathogenesis. Competition for nutritional iron was also studied through a plant-bacterial cell system: iron incorporated into plant ferritin appeared to be considerably reduced in bacteria-treated suspension soybean cells. l h e same effect was visualized during treatment of soybean cells with axenic leaf intercellular fluid from E. chrysanthemi-inoculated saintpaulia leaves or with chrysobactin.

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Finding sustainable plant protection strategies is a major challenge for agriculture. Taking advantage of the plant natural immune system by using plant defence elicitors is an interesting avenue to explore. However, transfer to field application is often difficult, mostly due to the complexity of interactions between plants and their environment, involving biotic and abiotic stresses. The protection efficacy against gray mold and the modes of action of potential elicitors were studied on tomato. Modulation of plant defense was studied using both global and targeted metabolic profiling. We identified seven potential elicitors showing good plant protection efficacy and able to trigger the oxylipin pathway, including jasmonic acid production, after inoculation with . Following preliminary assays, seven elicitors including two well-studied elicitors (Bion 50WG® and BABA) showing good plant protection efficacy and low fungitoxic effect were selected to assay the effect of abiotic stresses (wounding, water stress and nitrogen deficiency) on their protection efficacy. Our results showed that the protection efficacy of all products was reduced when plants were exposed to abiotic stresses, suggesting an antagonistic interaction between the tomato responses to abiotic stresses and product treatments. We found that responses to leaf cuttings and product treatments induced metabolic changes in a time-dependent manner, and that both of which mainly activated the oxylipin and JA pathway. However, the negative effects of wounding on tomato protection efficacy of defence elicitors suggest that interplay with other antagonistic signalling pathways is also involved in the tomato responses to this combination of stress.

To incite a systemic disease on its specific host, Saintpaulia ionantha, the soft-rot Erwinia chrysanthemi strain 3937 requires a functional high affinity iron transport system. Under iron starvation, strain 3937 produces chrysobactin, a novel catechol-type siderophore. Recent advances in the biochemistry and genetics of iron assimilation in E. chrysanthemi are reported. Analysis of leaf intercellular fluid from healthy and infected plants suggests: (i) leaf vessels in which the bacteria develop during infection would be low in free iron and (ii) chrysobactin could be produced in planta.

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