Plant Physiol. (1995) 108: 841 -842
Plant Gene Register
A Petunia c D N A Encoding S-Adenosylmethionine Syntketase’ Anat Izhaki, Oded Shoseyov, and David Weiss* The Kennedy Leigh Centre for Horticultural Research, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 761 00, Israel The biosynthesis of SAM from ATP and Met is catalyzed by SAM-S (EC 2.5.1.6). SAM has been found to participate in a large number of biological processes. It acts as a methyl group donor in numerous highly specific transmethylations involving various kinds of acceptor macromolecules, such as proteins, lipids, polysaccharides, and nucleic acids. It also serves as a propylamine group donor in the biosynthesis of polyamines (Peleman et al., 1989b).In plants, SAM also functions as a precursor in the biosynthesis of the phytohormone ethylene (Yang and Hoffman, 1984).SAM-S genomic and cDNA clones have been isolated from several plant species, including Arabidopsis tkaliana, carnation, parsley, poplar, and rice (van Breusegem et al., 1994). The saml gene of A . tkaliana is expressed primarily in the vascular tissue (Peleman et al., 1989a).The level of expression of this gene in stems and roots is 10 to 20 times higher than in leaves or flowers (Peleman et al., 1989b).In rice, a s i m i l a r level of sam expression has been found in leaves and roots (van Breusegem et al., 1994). In parsley leaves, a funga1 elicitor induces the expression of the gene (Kawalleck et al., 1992). Here we report the isolation, sequencing, and expression characteristics of a Petunia kybrida cDNA clone coding for SAM-S (Table I). A cDNA library prepared from mRNA isolated from petunia corollas at developmental stage 4 (Weiss and Halevy, 1989) was differentially screened using cDNA probes from corollas at stages 1 and 4. After several rounds of purification and differential hybridization one clone was obtained. Using this clone as a probe on a corolla cDNA library, we obtained several cDNAs. The nucleotide sequence of the longest cDNA was determined. Translation of this sequence revealed an open reading frame of 1173 bp corresponding to a polypeptide of 391 amino acids. The deduced amino acid sequence revealed 88% identity with the saml sequence of A. thaliana and 86% with the sam2 gene from carnation (Larsen and Woodson, 1991). A conserved amino acid sequence involved in ATP binding (GAGDQG;Kamps et al., 1984)is located at positions 119 to 124. An expression study of the sam2 gene in carnation flowers shows a decrease in the steady-state mRNA level during senescence (Woodson et al., 1992). An analysis of sam expression during petunia corolla maturation showed that
Table 1. Characteristics o f a sam cDNA clone from petunia Organism: Petunia hybrida cv VR. Enzyme: SAM-S. Clone, Source: pPSAM1, isolated from a AGEM-4 cDNA library constructed from poly(A)+ RNA of petunia corollas at stage 4 of flower development (Weiss and Halevy, 1989). Clon i ng Tec hn ique : Differential screening using cDNA probes from corollas at stages 1 and 4. Sequencing Techniques: Taq dideoxy terminator cycle sequencing of miniprep plasmid DNA; synthetic oligonucleotides to the known sequence used as primers; sequencing of both strands. cDNA Characteristics: Contains 1565 nucleotides consisting of 60 nucleotides in the 5’ untranslated region, 11 73 nucleotides in an open reading frame, and 332 nucleotides in the 3’ untranslated region followed by 15 b p of poly(A) tail. Structural Features of the Encoded Protein: The deduced amino acid sequence is 88% identical with the Arabidopsis saml gene and 86% identical with the saml gene of carnation. The putative ATP-binding site is at amino acid positions 119 t o 124. Expression Characteristics: Petunia sam gene is highly expressed in young leaves, stems, sepals, and corollas. The steady-state sam mRNA level i s low at the early stages of corolla growth. At stage 3 of flower development, the sam transcript rapidly accumulates and reaches a maximum level just before anthesis. After flower opening, the sam mRNA level starts to decline. Gene Copy Number: Small multigene family (two or three genes).
it is developmentally controlled. At an early stage of flower development (stage l), the transcript level is low. At approximately stage 3 of corolla maturation, the transcript rapidly accumulates, reaching a maximum level just before anthesis. After flower opening, the level of sam mRNA starts to decline. Woodson et al. (1992) related the decline in sam expression during the senescence of carnation flowers to the overall decrease in demand for SAM as a result of decreased inacromolecule synthesis. We suggest that the increase in sam expression during the early stages of petunia corolla growth (stage 3) is related to the rapid growth
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This w o r k was supported by a grants f r o m the European Economic Community (3837). * Corresponding author; e-mail
[email protected]; fax 972-8468263.
Abbreviations: SAM, S-adenosylmethionine; SAM-S, S-adenosylmethionine synthetase. 84 1
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of t h e tissue (Weiss and Halevy, 1989), which is probably accompanied b y an increase in macromolecule synthesis. Analysis of sam expression i n different organs of petunia plants showed a similar transcript leve1 in corollas (stage 5 ) and young leaves, sepals, and stems. Received November 3,1994; accepted December 20,1994. Copyright Clearance Center: 0032-0889/95/l08/0841/02. The EMBL accession number for the sequence reported in this article is X82214. LITERATURE CITED
Kamps MP, Taylor SS, Sefton BM (1984) Direct evidence that oncogenic tyrosin kinases and cyclic AMP-dependent protein kinase have homologous ATP-binding sites. Nature 3 1 0 589-592 Kawalleck P, Plesch G, Hahlbrock K, Somssich IE (1992) Induction by funga1 elicitor of S-adenosyl-L-methionine synthetase and S-adenosyl-L-homocysteine hydrolase mRNAs in cultured cells and leaves of Petraselinum crispum. Proc Natl Acad Sci USA 89: 4713-4717
Plant Physiol. Vol. 108, 1995
Larsen PB, Woodson WR (1991) Cloning and nucleotide sequence of a S-adenosylmethionine synthetase cDNA from carnation. Plant Physiol 9 6 997-999 Peleman J, Boerjan W, Engler G, Seurinck J, Botterman J, Alliotte T, Van Montagu M, Inze D (1989a) Strong cellular preference in the expression of a housekeeping gene of Arabidopsis tkaliana encoding S-adenosylmethionine synthetase. Plant Cell 1: 81-93 Peleman J, Saito K, Cottyn B, Engler G , Seurinck J, Van Montagu M, Inze D (198913) Structure and expression of the S-adenosylmethionine synthetase gene family in Arabidopsis tkaliana. Gene 8 4 359-369
van Breusegem F, Dekeyser R, Gielen J, Van Montagu M, Caplan A (1994) Characterization of a S-adenosylmethionine synthetase gene in rice. Plant Physiol 105: 1463-1464 Weiss D, Halevy AH (1989) Stamens and gibberellin in the regulation of corolla pigmentation and growth in Petunia hybrida. Planta 179: 89-96 Woodson WR, Park KY, Drory A, Larsen PB, Wang H (1992) Expression of ethylene biosynthetic pathway transcripts in senescing carnation flowers. Plant Physiol 99: 526-532 Yang SF, Hoffman NE (1984) Ethylene biosynthesis and its regulation in higher plants. Annu Rev Plant Physiol 35: 155-189
