In most bacteria, Fur (ferric uptake regulator) is a crucial global regulator known to operate not only in the regulation of iron homeostasis but also in a variety of other cellular processes. In an effort to characterize the role of Fur in the virulence of plant pathogens, a fur homolog was isolated from Pseudomonas syringae pv. tabaci 11528. Phenotype assays showed that a fur deletion mutant (BL33) constitutively produced siderophore(s) and exhibited decreases in swarming motility as well as the synthesis of tabtoxin and N-acyl homoserine lactones. Consistent with the results of TLC, quantitative real-time RT-PCR of the QS associated genes psyR and psyI demonstrated that Fur up-regulates these genes at the transcriptional level. Finally, the effects of a fur mutation on plant virulence indicated that Fur-regulated traits are relevant to plant-pathogen interactions. (C) 2007 Elsevier Inc. All.rights reserved.