Nucleotide sequences of the Pseudomonas savastanoi indoleacetic acid genes show homology with Agrobacterium tumefaciens T-DNA

Abstract

We report the nucleotide sequences of iaaM and iaaH, the genetic determinants for, respectively, tryptophan 2-monooxygenase and indoleacetamide hydrolase, the enzymes that catalyze the conversion of L-tryptophan to indoleacetic acid in the tumor-forming bacterium Pseudomonas syringae pv. savastanoi. The sequence analysis indicates that the iaaM locus contains an open reading frame encoding 557 amino acids that would comprise a protein with a molecular weight of 61,783; the iaaH locus contains an open reading frame of 455 amino acids that would comprise a protein with a molecular weight of 48,515. Significant amino acid sequence homology was found between the predicted sequence of the tryptophan monooxygenase of P. savastanoi and the deduced product of the T-DNA tms-) gene of the octopine-type plasmid pTiA6NC from Agrobacteium tumefaciens. Strong homology was found in the 25 amino acid sequence in the putative FAD-binding region of tryptophan monooxygenase. Homology was also found in the amino acid sequences representing the central regions of the putative products of iaaH and tms-2 T-DNA. The results suggest a strong similarity in the pathways for indoleacetic acid synthesis encoded by genes in P. savastanoi and in A. tumefaciens T-DNA.The association of the tumor-forming bacterium Pseudomonas syringae pv. savastanoi (P. savastanoi) and its hosts, oleander and olive plants, provides a system for studying the molecular basis of virulence of a bacterium in plants. Tumor formation by these plants is a response to high concentrations of indoleacetic acid (IAA) introduced into infected tissue by the bacterium (1); thus, production of a tumor is used to assess virulence of the bacterium. The bacterium produces IAA from tryptophan, with indoleacetamide as the intermediate. The enzymes involved are tryptophan 2-monooxygenase [L-tryptophan:oxygen 2-oxidoreductase (decarboxylating), EC 1.13.12.3], which catalyzes the conversion of L-tryptophan to indole-3-acetamide, and indoleacetamide hydrolase, which catalyzes the conversion of indoleacetamide to ammonia and IAA (2).The genes for the two enzymes, iaaM and iaaH, are part of an operon that is borne on a plasmid, pIAA, in oleander strains of the pathogen; in olive strains these genes are on the chromosome. Mutants cured of pIAA are weakly virulent on oleander; when transformed with pIAA,

Ti plasmid conjugation is independent of vir: reconstitution of the tra functions from pTiC58 as a binary system

“…This is an especially interesting possibility considering that the iaaH and iaaM genes of Pseudomonas syringae pv. savastanoi, which code for the synthesis of indol-3-acetic acid by this bacterium, are related at the nucleotide sequence level to those encoded on the T region of octopine-and nopaline-type Ti plasmids (52). That the Ti plasmid may be transmissible to P. syringae pv.…”

Plant Growth Promotion Efficacy of Indole Acetic Acid (IAA) Produced by a Mangrove Associated Fungi-Trichoderma viride VKF3

“…One of the roles suggested for production of IAA by fungus is to mediate fungal-plant interaction. A high concentration of IAA inhibited the hypersensitive response (Robinette and Matthysse, 1990;Jouanneau et al, 1991) and suppressed the expression of plant defense genes (Yamada et al, 1985;Shinshi et al, 1987). The present study focuses on production and characterization of IAA produced by the isolate T. viride VKF3.…”

Molecular cloning and characterization of an amidase from Arabidopsis thaliana capable of converting indole-3-acetamide into the plant growth hormone, indole-3-acetic acid

“…1, the corresponding amino acid sequences of the encoded polypeptides, AtAMIX to AiAMI4, are compared with the prokaryotic sequences and particularly to that of Rhodococcus sp. amidohydrolase (EC 3.5.1.4, GenBank M74531), an enzyme known to hydrolyze IAM into IAA and ammonia (Klee et al, 1984;Yamada et al, 1985), but utilizing also, e.g., fatty acid amides (Cravatt et al, 1996) as substrates. The active site of this enzyme has been analyzed in most detail (Kobayashi et al, 1997) and was shown to include Asp-168 and Ser-173 rather than Cys-181, a residue hitherto assumed to be involved in catalysis (Fig.…”