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L-Lysine Synthetase Is Encoded Solely by Open Reading Frame-2

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L-Lysine Synthetase Is Encoded Solely by Open Reading Frame-2 Proc. Nati. Acad. Sci. USA Vol. 87, pp. 5797-5801, August 1990 Biochemistry Expression and fine structure of the gene encoding NE-(indole-3-acety1)-L-Iysine synthetase from Pseudomonas savastanoi (plant hyperplasia/amino acid conjugate) FRANCISCO F. ROBERTO*t, HARRY KLEE*, FRANK WHITE§, RUSSELL NORDEEN*¶, AND TSUNE KOSUGE*II tMonsanto, Chesterfield, MO 63198; §Department of Plant Pathology, Kansas State University, Manhattan, KS 66506; and *Department of Plant Pathology, University of California, Davis, CA 95616 Communicated by Eric E. Conn, May 18, 1990 (receivedfor review March 12, 1990) ABSTRACT The gene encoding NI-(indole-3-acetyl)-L-Iy- MATERIALS AND METHODS sine synthetase, iaaL, from Pseudomonas savastanoi was local- ized within a 4.25-kilobase EcoRI fragment derived from Bacterial Strains, Media, and Plasmids. E. coli HB101 pIAAl of oleander strain EW 2009. Two open reading frames (pLG87) (11), HB101 (pLG87X), E. coli K38 (pMON686), of 606 and 1188 nucleotides were identified upon sequencing, K38 (pMON686ARV), K38 (pMON676), and pLG/SK were which directed the in vitro synthesis ofMr 21,000 andMr 44,000 used for plasmid DNA isolations, DNA sequencing, and proteins. Expression of an open reading frame-2 subclone, enzyme assays. Restriction enzyme sites for these plasmids pMON686, in Escherichia cofi indicates that (indole-3-acetyl)- derived from P. savastanoi pIAA1 and their orientation L-lysine synthetase is encoded solely by open reading frame-2. relative to one another are shown in Fig. 1. Bacteria were Hydrophobicity plots of the deduced open reading frame-1 maintained on LB agar plates incubated at 370C, and cells protein suggest that it may be a membrane-bound protein, used for plasmid isolations were grown in LB liquid medium whereas the predicted iaaL gene product possesses considerable (broth). Plasmids were maintained on medium supplemented hydrophilic character, consistent with the demonstration of with ampicillin (50 ,ug/ml). (indole-3-acetyl)-L-lysine synthetase activity in cell-free aque- Recombinant DNA Techniques. Restriction enzyme diges- ous extracts. No nucleotide or protein homologies were found tions, ligations, plasmid isolation, and purification were between iaaL and any sequences contained within the GenBank performed as described by Maniatis et al. (13). or National Biomedical Research Foundation data bases (April Nucleotide Sequence Determination. Unidirectional exonu- 13, 1989). clease III deletions (14) were performed to produce a set of nested clones derived from pLG87, cloned in both orienta- tions within pUC8. Except where noted, the DNA sequence Infection and colonization ofolive and oleander plants by the was obtained from denatured double-stranded templates us- plant pathogenic bacterium Pseudomonas syringae pv. ing pUC/M13 universal and reverse sequencing primers savastanoi (P. savastano) is manifested by the appearance of (New England Biolabs) and the cloned Klenow fragment of hyperplasias termed "galls" (1-3). The production of indole- DNA polymerase I, as described (15). Other sequence infor- 3-acetic acid (IAA) and cytokinins by the bacterium is mation was obtained from single-stranded templates gener- necessary for the elicitation ofthis response in the plant, and ated from pLG/SK (4.25-kb EcoRI fragment from pLG87 therefore, these bacterially produced compounds are viru- cloned in pBSSK+; Stratagene) and pMON676 using Seque- lence factors in the disease interaction (4, 5). Further me- nase (modified phage 17 DNA polymerase; United States tabolism ofIAA has been observed in P. savastanoi oleander Biochemical) according to the manufacturer's instructions. isolates, and the amino acid conjugate, N6-(indole-3-acetyl)- DNA sequence analysis was performed with the GCG soft- L-lysine (IAA-lysine), and an acetylated derivative, N"- ware package (16) and protein homology searches were acetyl-N6-(indole-3-acetyl)-L-lysine (N-acetyl-IAA-lysine) performed using the FASTA program ofPearson and Lipmann are found in culture filtrates of P. savastanoi (6-8). (17). The genes for synthesis of phytohormones reside on the In Vitro Protein Synthesis. DNA fragments spanning the 52-kilobase (kb) plasmid, pIAA1, in oleander strain EW2009 iaaL locus were cloned into plasmid pT7-7, where they were (9, 10). A 4.25-kb EcoRI fragment was found to confer on placed under the control ofthe phage 17 promoter (18). These Escherichia coli the ability to synthesize IAA-lysine from plasmids were introduced into E. coli K38 containing the IAA, and transposon mutations in the IAA-lysine synthetase plasmid pGP1-2, which directs the production of 17 RNA locus in P. savastanoi were obtained by marker exchange polymerase (18). Proteins were induced in the presence of (11, 12). The mutants showed an increase in IAA accumu- [35S]methionine and analyzed by electrophoresis on a 12.5% lation and were attenuated in virulence and in their ability to polyacrylamide gel containing SDS as described (18). grow within the plant (12). Therefore, the IAA-lysine syn- Enzyme Assay. Bacterial cells were grown overnight in 2 ml thetase gene represents an additional bacterial locus that of LB broth supplemented with and kanamycin influences microbial-plant interactions. ampicillin The locus for IAA-lysine synthesis has not been fully Abbreviations: IAA, indole-3-acetic acid; IAA-lysine, N'-(indole-3- characterized, and the number of genes involved is not acetyl)-L-lysine; N-acetyl-IAA-lysine, N"-acetyl-N'-(indole-3-ace- known. We report here the determination of the nucleotide tyl)-L-lysine. sequence** of the IAA-lysine synthetase gene iaaL and tPresent address: Biotechnology, Idaho National Engineering Lab- demonstrate that iaaL is sufficient for IAA-lysine production oratory, Idaho Falls, ID 83415-2203. in E. coli. VPresent address: U.S. Department of Agriculture, Beltsville Agri- cultural Research Center West, Plant Molecular Biology Labora- tory, Beltsville, MD 20705. The publication costs of this article were defrayed in part by page charge "Deceased, March 13, 1988. payment. This article must therefore be hereby marked "advertisement" **The sequence reported in this paper has been deposited in the in accordance with 18 U.S.C. §1734 solely to indicate this fact. GenBank data base (accession no. M35373). 5797 Downloaded by guest on October 1, 2021 5798 Biochemistry: Roberto et al. Proc. Natl. Acad Sci. USA 87 (1990) A R V ,0tT v vc R pLG87 111 11I orfl orf2 I 1k N L pMON686 p7z N C pTI7_ pMON686ARV B R V x V VC R I I II ~~-~ ~ ~ - ~ ~ - ~~- - -- --~ FIG. 1. Maps of clones used, TnS insertions, and sequencing strategy. (A) pLG87 is shown. R, EcoRI; V, EcoRV; X, Xba I; C, Cla I; N, Nde I. Other subclones are shown oriented to pLG87. Inserts in pMON686 and pMON686ARV are under the control of the bacteriophage T7 promoter. Tn5 insertions are depicted above the map. Solid circles indicate that the TnS insertion inactivates iaaL. Open circles indicate that the TnS insertion has no effect on iaaL. (B) DNA sequencing strategy. Sequence information obtained from double-stranded templates (pLG87 deletions) is depicted by solid arrows, with arrowheads indicating the direction and extent of the sequencing reaction away from primer; dashed arrows indicate sequences obtained from single-stranded templates (generated from pLG/SK) and oligonucleotide primers. (required for maintenance of pGP1-2) at 28°C. A 0.4-ml was eluted with two 1.5-ml volumes of methanol. The eluate sample from the overnight culture was inoculated into 40 ml was dried in a vacuum centrifuge and resuspended in 0.05 ml of LB broth containing antibiotics and incubated for 5 hr at of distilled H20. A 6-Al sample was applied to a precoated 28°C in 125-ml flasks. The cultures were heated to 42°C in a silica gel 60 plate (HPTLC; EM Science). [3H]IAA (4 pul at 10 water bath with gentle shaking and then incubated at 37°C for ,uCi/ml) and IAA-lysine (6 p.l at 10 mg/ml) were applied as 1 hr. The bacteria were harvested by centrifugation and standards. The chromatogram was developed in butanol/ resuspended in 10 ml of0.05 M Tris'HCl/0.02 M 2-mercapto- acetic acid/water, 4:1:4 (vol/vol). After drying, the chro- ethanol, pH 8.0. The samples were chilled on ice for 15 min matogram was sprayed with 0.2% ninhydrin. After visualiz- and lysed by sonication. Sonication was performed for two ing the amino acid-positive spots, the treated plate was 30-sec pulses with a 1-min interval at 100 W by using the fluorographed. standard probe on a Braun Sonic 2000 sonicator. Each lysate was centrifuged for 20 min at 17,000 rpm in a Ti 70 (Beckman RESULTS Instruments) rotor at 4°C. The lysate was kept on ice and a sample was removed for measurement of IAA-lysine synthe- DNA Sequence Determination. A previous study (11) de- tase activity. scribed TnS insertions in the left halfofpLG87 that prevented Activity was assayed in a total reaction volume of 0.6 ml expression of IAA-lysine synthetase, whereas two insertions for each lysate in a 1.5-ml Eppendorf tube. The reaction farther downstream had no effect (Fig. LA). Exonuclease mixture consisted of 28 mM K2HPO4 (pH 7.8), 0.5 mM III-generated deletion subclones were produced from pLG87 MnCl2, 0.5 mM MgCl2, 16.7 mM L-lysine, 1.3 mM ATP, 55 and sequenced through the second EcoRV site (solid arrows, ,uM IAA, to which 4 ul of [3H]IAA (specific activity, 21.7 Fig. 1B) revealing two open reading frames (ORFs). The first Ci/mmol, 1 Ci/ml; 1 Ci = 37 GBq; Amersham) and 0.28 ml ORF (ORF1) contained 606 nucleotides and is predicted to of lysate were added. The reaction mixtures were incubated encode a polypeptide containing 202 amino acids with a for 2 hr at 28°C at which time 0.3 ml of 10% (wt/vol) molecular weight of 21,000 (Fig.
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