Aromatic aminotransferase activity and indoleacetic acid production in Rhizobium meliloti

Kittell, Barbara L.; Helinski, Donald R.; Ditta, Gary S.

doi:10.1128/jb.171.10.5458-5466.1989

Cited by 60 publications

(42 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…To construct pMK413, the 1.7-kb cos fragment of pRK311 (9) Activity stains in nondenaturing polyacrylamide gels. The protocol of Kittell et al (29) was modified to include stacking and resolving phases in the separation system. Nondenaturing (native) gels contained 10% acrylamide (9.7% acrylamide, 0.3% bisacrylamide) in the resolving phase and 5% acrylamide (4.85% acrylamide, 0.15% bisacrylamide) in the stacking phase.…”

Section: Methodsmentioning

confidence: 99%

Cloning and mutagenesis of the Rhizobium meliloti isocitrate dehydrogenase gene

McDermott

Kahn

1992

J Bacteriol

View full text Add to dashboard Cite

The gene encoding Rhizobium meliloti isocitrate dehydrogenase (ICD) was cloned by complementation of an Escherichia coli icd mutant with an R. meliloti genomic library constructed in pUC18. The complementing DNA was located on a 4.4-kb BamHI fragment. It encoded an ICD that had the same mobility as R. meliloti ICD in nondenaturing polyacrylamide gels. In Western immunoblot analysis, antibodies raised against this protein reacted with R. meliloti ICD but not with E. coli ICD. The complementing DNA fragment was mutated with transposon TnS and then exchanged for the wild-type allele by recombination by a novel method that employed the Bacillus subtilis levansucrase gene. No ICD activity was found in the two R. meliloti icd::Tn5 mutants isolated, and the mutants were also found to be glutamate auxotrophs. The mutants formed nodules, but they were completely ineffective. Faster-growing pseudorevertants were isolated from cultures of both R. melloti icd::Tn5 mutants. In addition to lacking all ICD activity, the pseudorevertants also lacked citrate synthase activity. Nodule formation by these mutants was severely affected, and inoculated plants had only callus structures or small spherical structures.In the symbiosis between legumes and rhizobia, the host plant provides the bacteria with reduced carbon as an energy source. The bacteria use this energy to reduce atmospheric nitrogen to ammonia, which they release to the plant. The qualitative nature of this energy source has been the focus of much research. Sucrose is the major photosynthate transported from the shoot to the nodule (41), but biochemical evidence suggests that neither sucrose nor hexoses obtained from sucrose degradation are important sources of energy for the bacteroids (reviewed in references 7 and 34). In support of this conclusion, mutants of various species of rhizobia with defects in sugar metabolism have been found to be effective in symbiosis (7,34). By contrast, dicarboxylic acids appear to be important carbon sources in the establishment of an effective symbiosis. Succinate and malate are found at high concentrations in nodules (14,45,55), are actively transported across the peribacteroid membrane (20,56), are taken up by bacteroids (11,20,42,50), and are quickly oxidized to CO2 after uptake (47). Dicarboxylic acid transport (dct) mutants of Rhizobium meliloti (5) and R. leguminosarum biovars viciae (3, 12) and trifolii (44) We are interested in how the bacteroid TCA cycle is regulated and have selected ICD for our initial studies because it is a regulated enzyme at a branch point in the TCA cycle (15), because it is regulated by aerobiosis in other gram-negative bacteria (23, 24), and because it is a relatively simple enzyme with a single type of subunit that, in other bacteria, is encoded by a single gene (2). In this study, we report the isolation of the gene that encodes ICD in R meliloti and the symbiotic properties of mutants with defects in this gene. MATERIALS AND METHODSBacterial strains and plasmids. The strains of R. meliloti and Es...

show abstract

Section: Methodsmentioning

confidence: 99%

Cloning and mutagenesis of the Rhizobium meliloti isocitrate dehydrogenase gene

McDermott

Kahn

1992

J Bacteriol

View full text Add to dashboard Cite

show abstract

“…Aromatic amino acid aminotransferases, which can transfer the ␣-amino group of aromatic amino acids to a ketoacid acceptor, have been studied in various microorganisms including E. coli, Klebsiella aerogenes, A. brasilense, Sinorhizobium meliloti, Bacillus brevis, and Pseudomonas aeruginosa; some of them have already been purified (25,33,42,52,63). Generally, two or more enzymes with overlapping specificities are found in the same microorganism (28,44). Aromatic amino acid aminotransferases have already been shown to play a role in IAA and PAA biosynthesis in bacteria and fungi (20,27,28,48).…”

Section: Using Anmentioning

confidence: 99%

“…Generally, two or more enzymes with overlapping specificities are found in the same microorganism (28,44). Aromatic amino acid aminotransferases have already been shown to play a role in IAA and PAA biosynthesis in bacteria and fungi (20,27,28,48).…”

Section: Using Anmentioning

confidence: 99%

Azospirillum brasilense Produces the Auxin-Like Phenylacetic Acid by Using the Key Enzyme for Indole-3-Acetic Acid Biosynthesis

Somers

Ptacek

Gysegom

et al. 2005

Appl Environ Microbiol

134

View full text Add to dashboard Cite

An antimicrobial compound was isolated from Azospirillum brasilense culture extracts by high-performance liquid chromatography and further identified by gas chromatography-mass spectrometry as the auxin-like molecule, phenylacetic acid (PAA). PAA synthesis was found to be mediated by the indole-3-pyruvate decarboxylase, previously identified as a key enzyme in indole-3-acetic acid (IAA) production in A. brasilense. In minimal growth medium, PAA biosynthesis by A. brasilense was only observed in the presence of phenylalanine (or precursors thereof). This observation suggests deamination of phenylalanine, decarboxylation of phenylpyruvate, and subsequent oxidation of phenylacetaldehyde as the most likely pathway for PAA synthesis. Expression analysis revealed that transcription of the ipdC gene is upregulated by PAA, as was previously described for IAA and synthetic auxins, indicating a positive feedback regulation. The synthesis of PAA by A. brasilense is discussed in relation to previously reported biocontrol properties of A. brasilense.Azospirillum is a well-studied genus of plant growth-promoting bacteria (PGPB), which colonizes the rhizosphere of numerous crop plants in tropical and subtropical regions (5, 6). Different mechanisms, such as phytohormone production, nitrate reduction, and nitrogen fixation, have been proposed to explain improved plant growth following inoculation with Azospirillum (5,7,9,22,37,38,53). The production of phytohormones, and more specifically the auxin indole-3-acetic acid (IAA), has been recognized as an important factor in direct plant-growth-promoting abilities of A. brasilense (5,18,19,37).Azospirillum sp. are not typical biocontrol agents of soilborne plant pathogens (5). Apart from some reports on bacteriocins and siderophores, no other antibacterial substances in Azospirillum sp. have been identified so far (39,40,50,55,60). However, there have been reports of moderate biocontrol capabilities of Azospirillum brasilense against crown gall disease, bacterial leaf blight of mulberry, and bacterial leaf and/or vascular diseases of tomato (1,3,4,46,54). In addition, A. brasilense can restrict the proliferation of other nonpathogenic rhizosphere bacteria (21). Nevertheless, the exact mechanisms involved in Azospirillum acting as a putative biocontrol agent are not yet known. Some reports therefore indicate that the protective mechanism may be indirectly explained by the plant growth promotion effect or by outcompeting other bacteria hosted by the same plant (3,46).In the present study, we attempted to further screen A. brasilense supernatant (extracts) for the presence of metabolites (besides IAA), which may be involved in the persistence of Azospirillum in the rhizosphere. This screening led to the identification of phenylacetic acid (PAA), an auxin-like molecule with antimicrobial activity. MATERIALS AND METHODSStrains, plasmids, media, and culture conditions. Strains and plasmids used in this study are listed in Table 1. A. brasilense was grown at 30°C in Luria-Bertani (LB) med...

show abstract

“…Nevertheless, B. japonicum with mutated nodA, nodB, nodC, or nodD genes still produce cytokinins. Genes involved in auxin biosynthesis have been cloned from B. japonicum (Sekine, Watanabe & Syono, 1989) and R. meliloti (Kittell, Helinski & Ditta, 1989). However, the effects of mutations in these genes on establishing the symbiosis have not been studied.…”

Section: The Second Signal For Nodule Morphogenesis: Role For Thementioning

confidence: 99%

Developmental biology of legume nodulation

1992

View full text Add to dashboard Cite

SUMMARY Many legumes respond to Rhizobium inoculation by developing unique structures known as nodules on their roots. The development of a legume nodule in which rhizobia convert atmospheric N2 into ammonia is a finely tuned process. Gene expression from both partners of the symbiosis must be temporally and spatially coordinated. Exactly how this coordination takes place is an area of intense study. Nodule morphogenesis appears to be elicited by at least two distinct signals: one from Rhizobium, a product of the nod genes (Nod factor), and a second signal, which is generated within plant tissues after treatment with Nod factor. The identity of the second signal is unknown but changes in the balance of endogenous plant hormones or the sensitivity of plant tissues to these hormones are likely to be involved. These hormonal changes may be triggered by endogenous flavonoids produced by the root in response to inoculation with Rhizobium. There is some controversy as to whether the legume nodule is an organ sui generis or a highly derived lateral root. A resolution of this question may become more critical as attempts to induce nodules on non‐legume hosts, such as rice or maize, increase in number and scope.

show abstract

Aromatic aminotransferase activity and indoleacetic acid production in Rhizobium meliloti

Cited by 60 publications

References 43 publications

Cloning and mutagenesis of the Rhizobium meliloti isocitrate dehydrogenase gene

Cloning and mutagenesis of the Rhizobium meliloti isocitrate dehydrogenase gene

Azospirillum brasilense Produces the Auxin-Like Phenylacetic Acid by Using the Key Enzyme for Indole-3-Acetic Acid Biosynthesis

Developmental biology of legume nodulation

Contact Info

Product

Resources

About