A mutation in the indole-3-acetic acid biosynthesis pathway of Pseudomonas syringae pv. syringae affects growth in Phaseolus vulgaris and syringomycin production

Abstract

Homologs of the genes for indole-3-acetic acid (IAA) biosynthesis from Pseudomonas syringae pv. savastanoi were retrieved from a genomic library of P. syringae pv. syringae, and their nucleotide sequences were determined. Sequence relatedness between the P. syringae pv. syringae and P. syringae pv. savastanoi iaa operons is greater than 901% within the iaaM and iaaH loci but declines dramatically at a position approximately 200 bp 5' of the iaaM translation initiation codon. A third open reading frame was detected downstream of iaaH. Production of LIA was undetectable in mutant strain Y30-53.29, which was generated by transposition of TnS into the iaaM gene of P. syringae pv. syringae Y30. The IAA-deficient (LA-) mutant retained the ability to colonize the bean phylloplane and induced disease symptoms on bean which were similar to those produced by the parental strain. However, the population dynamics of the IAA-strain during the parasitic phase in leaves differed from those of both the parental strain and the mutant genetically restored for IAA biosynthesis. The mutant was capable of inducing disease symptoms when established in bean tissues at a lower initial cell density than either LIA-producing strain. Syringomycin biosynthesis by the IAA-strain was diminished in comparison with the parental strain or the mutant genetically restored for LIA production. The results indicate that bacterially derived IAA, or its biosynthesis, is involved in the regulation of in planta growth and in the expression of other factors that affect the host-pathogen interaction.The ability to produce indole-3-acetic acid (IAA) is widespread among soil and plant-associated microorganisms (17,25). Among phytopathogenic bacteria, production of IAA has been shown to play a causal role in the development of hyperplastic disease symptoms that are induced by certain species of bacteria. Production of IAA by plant cells after transformation with Agrobacterium tumefaciens and Agrobacterium rhizogenes is directed by the T-DNA genes and was shown to be a determinant for induction of hypertrophic plant growth after incorporation and expression within the host cells (1,51,55). These transformed plant cells produce IAA from L-tryptophan via the intermediate indole-3-acetamide (IAM). In this pathway, the enzyme tryptophan-2-monooxygenase catalyzes the conversion of tryptophan to IAM, and the conversion of IAM to IAA is catalyzed by the enzyme indoleacetamide hydrolase. Pseudomonas syringae pv. savastanoi also induces hyperplasia on its plant host, with symptoms varying from knots on oleander and olive to bark blisters and wart-like formations on ash (19). Induction of tumor formation by P. syringae pv. savastanoi on olive and oleander requires bacterial production of IAA (12, 49). As observed for crown gall cells, P. syringae pv. savastanoi produces IAA via the IAM pathway, and the genetic determinants for tryptophan-2-monooxygenase and indoleacetamide hydrolase (iaaM and iaaH, respectively) are part of an operon with iaaM promoter proximal (59). E...

Comparison of the complete genome sequences of Pseudomonas syringae pv. syringae B728a and pv. tomato DC3000

“…savastanoi (49). The genes in the operon are Ͼ90% identical to those in the IAA operon of Pss Y30 (47). Although Pst DC3000 has no orthologs of iaaM and iaaH, it produces IAA (8), possibly due to PSPTO0517 and PSPTO0518, which have low sequence similarity to tryptophan monooxygenase and indoleacetamide hydrolase, respectively.…”

“…Auxin. Bacterial indole-3-acetic acid (IAA) can have either a stimulatory or inhibitory effect on plant growth depending on its concentration and the plant tissue exposed (47). Most pathovars of P. syringae produce IAA (48), but the amounts produced vary greatly between strains.…”

“…Most pathovars of P. syringae produce IAA (48), but the amounts produced vary greatly between strains. Pss B728a produces substantially higher levels of IAA than Pst DC3000 in most culture media (T. Powell, personal communication), and IAA production is known to contribute to virulence and epiphytic fitness of Pss B728a (47). Pss B728a has an operon for biosynthesis of IAA, which includes tryptophan monooxygenase, iaaM (Psyr1536) and indoleacetamide hydrolase iaaH (Psyr1537), and genes first described in P. syringae pv.…”

The complete genome sequence of the Arabidopsis and tomato pathogen Pseudomonas syringae pv. tomato DC3000

“…However, DC3000 does contain five nonribosomal peptide synthases in three separate gene clusters (PSPTO2829, -2830, -4518, -4519, and -4699) that may direct the biosynthesis of undescribed peptide or lipodepsipeptide products. Production of the phytohormone indole-3-acetic acid (IAA) by certain P. syringae pathovars has been shown to influence bacterial growth in planta and the expression of other virulence factors (47,48). The two genes required for IAA production, iaaH and iaaM, are present in DC3000.…”

Activation of the Indole-3-Acetic Acid–Amido Synthetase GH3-8 Suppresses Expansin Expression and Promotes Salicylate- and Jasmonate-Independent Basal Immunity in Rice

“…In addition, R gene-mediated Xoo resistance accompanies the suppression of auxin signaling. A search of the amino acid sequences of Pseudomonas syringae pv syringae iaaH and iaaM (Mazzola and White, 1994) against the putative encoding products of the Xoo (strains KACC10331 and MAFF311018) whole genome sequence (Lee et al, 2005;Ochiai et al, 2005) did not reveal any homologous sequence. We then searched databases and found that Xoo carries NIT proteins (National Center for Biotechnology Information protein database accession numbers AAW74756, AAW74754, and YP_200139), which may contribute to the accumulation of IAA.…”