title: New insights into the role of indole-3-acetic acid in the virulence of Pseudomonas savastanoi pv. savastanoi.
abstract: Indole-3-acetic acid (IAA) is a widespread phytohormone among plant-associated bacteria, including the tumour-inducing pathogen of woody hosts, Pseudomonas savastanoi pv. savastanoi. A phylogenetic analysis of the iaaM/iaaH operon, which is involved in the biosynthesis of IAA, showed that one of the two operons encoded by Pseudomonas savastanoi pv. savastanoi NCPPB 3335, iaaM-1/iaaH-1, is horizontally transferred among bacteria belonging to the Pseudomonas syringae complex. We also show that biosynthesis of the phytohormone, virulence and full fitness of this olive pathogen depend only on the functionality of the iaaM-1/iaaH-1 operon. In contrast, the iaaM-2/iaaH-2 operon, which carries a 22-nt insertion in the iaaM-2 gene, does not contribute to the production of IAA by this bacterium. A residual amount of IAA was detected in the culture supernatants of a double mutant affected in both iaaM/iaaH operons, suggesting that a different pathway might also contribute to the total pool of the phytohormone produced by this pathogen. Additionally, we show that exogenously added IAA negatively and positively regulates the expression of genes related to the type III and type VI secretion systems, respectively. Together, these results suggest a role of IAA as a signalling molecule in this pathogen.
authors.affiliation: Área de Genética, Facultad de Ciencias, Instituto de Hortofruticultura Subtropical y Mediterrnea "La Mayora", Universidad de Málaga-CSIC (IHSM-UMA-CSIC), Málaga, Spain.
authors.forename: Isabel M
authors.initials: IM
authors.lastname: Aragón
authors.forename: Isabel
authors.initials: I
authors.lastname: Pérez-Martínez
authors.forename: Alba
authors.initials: A
authors.lastname: Moreno-Pérez
authors.forename: Miguel
authors.initials: M
authors.lastname: Cerezo
authors.forename: Cayo
authors.initials: C
authors.lastname: Ramos
mesh_terms: D053898:Biosynthetic Pathways / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D007210:Indoleacetic Acids / Q000378:metabolism*; D009876:Operon; D011549:Pseudomonas / Q000235:genetics* / Q000254:growth & development*; D014774:Virulence
chemical_list: D007210:Indoleacetic Acids; C030737:indoleacetic acid
keywords: T3SS; T6SS; auxin; indole-3-acetic acid; olive knot disease