Role of indoleacetic acid-lysine synthetase in regulation of indoleacetic acid pool size and virulence of Pseudomonas syringae subsp. savastanoi

Abstract

The phytopathogen Pseudomonas syringae subsp. savastanoi incites the production of galls on olive and oleander plants. Gall formation is dependent upon the bacterial synthesis of the phytohormone indole-3-acetic acid (IAA). Strains isolated from oleander galls are capable of further metabolizing IAA to an amino acid conjugate, 3-indoleacetyl-e-L-lysine (IAA-lysine); bacterial olive gall isolates lack this activity. In this study, the cloned gene for IAA-lysine synthetase (iaaL+) was introduced into strains isolated from olive and oleander galls to determine its effect on the regulation of IAA pool size and virulence. IAA-lysine was synthesized by isolates from olive galls when iaaL+ was introduced by conjugation, but the amount of IAA which accumulated in culture by the transconjugant was reduced by one-third. When the iaaL+ locus of an oleander gall isolate was inactivated by TnS mutagenesis, the resulting mutant did not convert IAA to IAA-lysine; however, it accumulated fivefold more IAA in culture than the wild type did. When inoculated into oleander plants, the iaaL mutant did not cause typical gall symptoms, nor did it replicate within host tissue similarly to the wild type.Pseudomonas syringae subsp. savastanoi (Smith 1908) Stevens incites the formation of tumorous outgrowths on olive (Olea europa L.) and oleander (Nerium oleander L.

Utilization of the Plant Hormone Indole-3-Acetic Acid for Growth by Pseudomonas putida Strain 1290

“…Symbiotic nitrogen fixation by nodules of B. japonicum on soybean apparently requires a carefully balanced level of IAA (41), which depends on the ability of the bacterium to degrade IAA (10,17,31). For optimal infection and colonization of olive and oleander, P. savastanoi requires a functional synthetase that converts IAA into the inactive IAA-lysine (15,39); knockout mutants showed accumulation of IAA, attenuation of virulence, and reduced growth in planta (11). P. putida 1290 most likely would exist in a nearly commensalistic association with plants since its ability to degrade IAA may function in homeostasis, i.e., balancing IAA-based interactions away from extremes that might lead to a parasitic relationship, but one that would benefit the bacterium.…”

Global Genomic Analysis of Pseudomonas savastanoi pv. savastanoi Plasmids

“…Previous analyses of the genetic content of P. savastanoi pv. savastanoi plasmids have demonstrated that they can carry virulence genes related to the biosynthesis of the phytohormones indole-3-acetic acid (iaaM, iaaH, and iaaL genes) (17,33,41) and cytokinins (25,30). Southern hybridization analysis 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

“…In the olive, the disease is considered to reduce both olive yield and productivity (41, 42); however, quantitative data on the impact of the disease on crop yield or crop quality are not available (19). Nevertheless, losses can be caused directly by localized infections that inhibit flowering and affect fruit development, as well as taste, and can be caused indirectly by weakening immature main leader branches that result in later damage to the tree frame (48).Currently, the only molecular P. savastanoi determinants known to be involved in knot development are the phytohormones indoleacetic acid (IAA) and cytokinins (1,15,33,38,45), as well as biosynthesis of a functional type III secretion system, encoded by the hrp-hrc gene clusters (43,44). Recently, a global genomic analysis of P. savastanoi pv.…”

“…Currently, the only molecular P. savastanoi determinants known to be involved in knot development are the phytohormones indoleacetic acid (IAA) and cytokinins (1,15,33,38,45), as well as biosynthesis of a functional type III secretion system, encoded by the hrp-hrc gene clusters (43,44). Recently, a global genomic analysis of P. savastanoi pv.…”