Population diversity of Pseudomonas syringae subsp. savastanoi on olive and oleander

Abstract

Twenty‐one strains of Pseudomonas syringae subsp. savastanoi, isolated from knots on olive and oleander trees growing in close proximity to or in physical contact with one another, were evaluated for knot induction and for bacteriocin production. In addition, DNA preparations from the bacterial strains were tested for hybridization to probes containing the tryptophan monooxygenase (iaaM) and isopentenyl transferase (ipt) genes, which are involved in indole‐3‐acetic acid and cytokinin biosynthesis, respectively, in P.s. subsp. savastanoi. The strains showed features characteristic of strains usually isolated from their respective host plants. For example, all 10 oleander strains were virulent both to oleander and olive, did not produce bacteriocins and harboured the iaaM gene on plasmids. In contrast, all 11 olive strains were virulent only to olive, 10 strains produced bacteriocins, and nine strains carried the iaaM gene on the chromosome. Two olive strains (OAll, OD21) harboured the gene coding for iaaM on plasmids. Furthermore, strain OD21 carried the iaaM gene on the same plasmid as the ipt gene. This is the first report both of a plasmid‐borne iaaM in typical olive strains (virulent only to olive and bacteriocin producers), and of the presence of the ipt gene on the same plasmid. In olive and oleander strains the ipt gene was located either on plasmids or on the chromosome. These results suggest that under natural conditions the pathogen does not appear to spread from oleander to olive even when trees are growing in close proximity or in physical contact. The location of the phytohormone genes on plasmids or on the chromosome is discussed in relationship to bacteriocin‐production and knot‐induction on the host species.

Abundance and diversity of the phyllosphere bacterial communities of Mediterranean perennial plants that differ in leaf chemistry

“…In consequence, only few papers have been published regarding fungal (Inacio et al 2002;Pereira et al 2002) or bacterial communities (Yadav et al 2004a;Karamanoli et al 2000;Caponero et al 1995;PØrissol et al 1993;Ercolani 1991). The Mediterranean environment, typified by the alternation of a cold and relatively wet period with a hot and dry one, is unique in that factors favouring growth (appropriate temperature regimes and water availability) do not coincide for a considerable part of the year.…”

Global Genomic Analysis of Pseudomonas savastanoi pv. savastanoi Plasmids

“…In fact, in most oleander isolates of P. savastanoi, the genes responsible for the biosynthesis of phytohormones are usually located in plasmids, which have been called pIAA and pCK for the biosynthesis of IAA and CKs, respectively (5,8,25). In contrast, most olive isolates have been reported to carry these genes in the chromosome (5,19). Native plasmids of P. savastanoi pv.…”

Pseudomonas savastanoi pv. savastanoi Contains Two iaaL Paralogs, One of Which Exhibits a Variable Number of a Trinucleotide (TAC) Tandem Repeat

“…nerii, iaaM and iaaH are organized in an operon with the iaaM locus first in the gene cluster (12). The IAA operon and the iaaL gene reside on a plasmid (pIAA) in P. savastanoi strains isolated from oleander galls (5,7,8,14); however, the direction of iaaL transcription has been determined to be opposite to IAA operon transcription (14). In contrast, most olive isolates have been reported to carry all three IAA genes on the chromosome (5,8,32).…”