Isolation and characterization of a Tritordeum cDNA encoding S-adenosylmethionine decarboxylase that is circadian-clock-regulated

Molecular cloning, expression analysis and chromosomal mapping of salt-responsive cDNAs in rice (Orym sativa L.)

By using differential display PCR (DD-PCR) technique, two salt-inducible and one salt-repressed cDNA fragments were isolated from rice. The three cDNA fragments were characterized respectively as partial sequence of rice S-adenosylmethionine decarboxylase (SAMDC) gene, a new member of translation elongation factor 1A gene (namedREF1 A), and a novel gene whose function is unknown (namedSRG1). The full-length cDNA of SAMDC gene (namedSAMDC1) was further isolated by RT-PCR approach and the deduced polypeptide was found to be homologous to SAMDC proteins of other plants, yeast and buman. Northern hybridization revealed that expression of SAMDCl and REFlA was induced, while SRGl was dramatically repressed, by salinity stress. Southern blot analysis demonstrated that SAMDCl and SRGl were present as a single copy gene in rice genome, whereas riceREF1 A gene was organized as a gene family. TheREF1 A,SAMDC1, andSRG1 genes were located on chromosome 3,4, and 6 respectively by RFLP mapping approach using ZYQ8/JX17 DH population and RFLP linkage maps.

Tissue-specific expression of olive S-adenosyl methionine decarboxylase and spermidine synthase genes and polyamine metabolism during flower opening and early fruit development

Polyamines (PAs) are required for cell growth and cell division in eukaryotic and prokaryotic organisms. The present study is aimed at understanding the developmental regulation of PA biosynthesis and catabolism during flower opening and early fruit development in relation to fruit size and shape. Two full-length cDNA clones coding for S-adenosyl methionine decarboxylase (SAMDC) and spermidine synthase (SPDS) homologs, key steps in the PA biosynthesis pathway, in the stone-fruit of olive (Olea europaea L.) were identified and the spatial and temporal organization of these genes were described. In olive flowers, OeSAMDC gene transcripts were highly expressed in ovary wall, placenta and ovules, while OeSPDS transcript was confined to the ovules of ovary at anthesis stage. A correlation was detected between the SAMDC enzyme activity/accumulation transcript and spermidine (Spd) and spermine (Spm) levels during flower opening, implying that the synthesis of decarboxylated SAM might be a rate-limiting step in Spd and Spm biosynthesis. OeSAMDC and OeSPDS transcripts were co-expressed in fruit mesocarp and exocarp at all developmental stages analyzed as well as in nucellus, integuments and inner epidermis tissues of fertilized ovules. In contrast, the OeSAMDC and OeSPDS genes had different expression patterns during early fruit development. The results provide novel data about localization of PA biosynthesis gene transcripts, indicating that transcript levels of PA biosynthesis genes are all highly regulated in a developmental and tissue-specific manner. The differences between the two olive cultivars in the fruit size in relation to the differences in the accumulation patterns of PAs are discussed.

BUD2, encoding an S-adenosylmethionine decarboxylase, is required for Arabidopsis growth and development

Polyamines are implicated in regulating various developmental processes in plants, but their exact roles and how they govern these processes still remain elusive. We report here an Arabidopsis bushy and dwarf mutant, bud2, which results from the complete deletion of one member of the small gene family that encodes S-adenosylmethionine decarboxylases (SAMDCs) necessary for the formation of the indispensable intermediate in the polyamine biosynthetic pathway. The bud2 plant has enlarged vascular systems in inflorescences, roots, and petioles, and an altered homeostasis of polyamines. The double mutant of bud2 and samdc1, a knockdown mutant of another SAMDC member, is embryo lethal, demonstrating that SAMDCs are essential for plant embryogenesis. Our results suggest that polyamines are required for the normal growth and development of higher plants.

A leader intron and 115-bp promoter region necessary for expression of the carnation S-adenosylmethionine decarboxylase gene in the pollen of transgenic tobacco

The expression of CSDC9 encoding S-adenosylmethionine decarboxylase (SAMDC) is developmentally and spatially regulated in carnation. To examine the regulation of the SAMDC gene, we analyzed the spatial expression of CSDC9 with a 5'-flanking beta-glucuronidase fusion in transgenic tobacco plants. GUS was strongly expressed in flower, pollen, stem and vein of cotyledons. Expression in both anther and stigma was under developmental control; analysis of a series of mutants with deletions of the 5'-flanking region demonstrated differential activation in petal, anther, stigma and pollen grains. All the major cis-regulatory elements required for pollen-specific transcription were located in the upstream region between -273 and -158. This region contains four putative elements related to gibberellin induction (pyrimidine boxes, TTTTTTCC and CCTTTT) and pollen-specific expression (GTGA and AGAAA). In addition, the first 5'-leader intron was necessary for tissue-specific expression.

Isolation of a novel barley cDNA encoding a nuclear protein involved in stress response and leaf senescence

In order to isolate genes involved in the early acclimation of winter barley (Hordeum vulgare L. cv. Trixi) to a combined cold and light stress of 2 degrees C and 600 micromol m(-2) s(-1) restriction fragment differential display-polymerase chain reaction was performed. Impact of the cold-treatment on the leaves was characterized by measuring chlorophyll content and photosystem II efficiency. By this approach several cDNAs of genes that quickly and transiently up-regulated during early stages of the stress were identified. One of these genes (HvFP1) includes sequence motifs representing a heavy metal associated domain (HMA), nuclear localization signals (NLS) and a farnesylation motif. This gene is also induced at drought stress, during leaf senescence and after exposure to abscisic acid. Analysis of its spatial expression patterns in barley plants either grown at 21 or 2 degrees C showed that in contrast to the situation in leaves transcript level of this gene is high not only in cold-treated plants but also in controls kept at 21 degrees C in plant compartments enriched in meristematic tissues. The nuclear localization of the protein was confirmed by confocal laser scanning microscopy of epidermal onion cells after particle bombardment with chimeric HVFP1-GFP constructs. Using a construct with a modified farnesylation motif yielded a different pattern of nuclear distribution of the chimeric protein.

Genomic characterization of the S-adenosylmethionine decarboxylase genes from soybean

A full-length gene GmSAMDC1, encoding the S-adenosylmethionine decarboxylase (SAMDC), a key enzyme involved in polyamine biosynthesis, was identified from soybean expressed sequence tags and was characterized. GmSAMDC1 encoded a peptide of 355 amino acids. When compared with other plant SAMDCs, the GmSAMDC1 protein had several highly conserved regions including a putative pro-enzyme cleavage site and a PEST sequence. The 5' leader sequence of the the GmSAMDC1 mRNA contained two additional open reading frames (ORFs), which may regulate the translational process. The genomic sequence of the GmSAMDC1 gene contained three introns in the 5' leader sequence, but no intron in the 3'-UTR or the main pro-enzyme ORF. A simple sequence repeat (SSR) was found in intron 2, and the GmSAMDC1 gene was mapped to linkage group D1 using this SSR. The genomic organization of the GmSAMDC1 gene in the subgenus Glycine and the subgenus Soja was found to be different by Southern-blot and PCR analysis. A pseudogene, GmSAMDC2, was also identified. This gene contained no intron and lost its two uORFs. Northern-blot analysis showed that the GmSAMDC1 gene expression was induced by salt, drought and cold, but not induced by wounding; suggesting that the gene was implicated in response to multiple-stress conditions.

Suppression of S-adenosylmethionine decarboxylase activity is a major cause for high-temperature inhibition of pollen germination and tube growth in tomato (Lycopersicon esculentum Mill.)

Possible involvement of impaired polyamine biosynthesis in the poor performance of tomato pollen (Lycopersicon esculentum Mill.) at high temperatures was investigated. Incubation of pollen at 38 degrees C suppressed the increase of S-adenosylmethionine decarboxylase (SAMDC) activity in germinating pollen with little influence on arginine decarboxylase activity. Consequently, spermidine and spermine content in the pollen did not increase at 38 degrees C, while putrescine content increased at both 25 degrees C and 38 degrees C. High-temperature inhibition of pollen germination was alleviated by the addition of spermidine or spermine but not of putrescine to the germination medium. Cycloheximide inhibited SAMDC activity in parallel with pollen germination at 25 degrees C, whereas actinomycin D had no effect on either of them, indicating that enhanced SAMDC activity is associated with de novo protein synthesis. Incubation of crude enzyme extracts at 40 degrees C for 1 h did not affect SAMDC. In addition, high temperatures did not enhance protease activity in germinating pollen. These results indicate that low activity of SAMDC, probably due to impaired protein synthesis or functional enzyme formation, is a major cause for the poor performance of tomato pollen at high temperatures.

Structural roles of cysteine 50 and cysteine 230 residues in Arabidopsis thaliana S-adenosylmethionine decarboxylase

The Arabidopsis thaliana S-Adenosylmethionine decarboxylase (AdoMetDC) cDNA (GenBank U63633) was cloned. Site-specific mutagenesis was performed to introduce mutations at the conserved cysteine Cys(50), Cys(83), and Cys(230), and lys(81) residues. In accordance with the human AdoMetDC, the C50A and C230A mutagenesis had minimal effect on catalytic activity, which was further supported by DTNB-mediated inactivation and reactivation. However, unlike the human AdoMetDC, the Cys(50) and Cys(230) mutants were much more thermally unstable than the wild type and other mutant AdoMetDC, suggesting the structural significance of cysteines. Furthermore, according to a circular dichroism spectrum analysis, the Cys(50) and Cys(230) mutants show a higher a-helix content and lower coiled-coil content when compared to that of wild type and the other mutant AdoMetDC. Also, the three-dimensional structure of Arabidopsis thaliana AdoMetDC could further support all of the data presented here. Summarily, we suggest that the Cys(50) and Cys(230) residues are structurally important.

Procedures allowing the transformation of a range of European elite wheat (Triticum aestivum L.) varieties via particle bombardment

Ten current European wheat varieties were transformed at efficiencies ranging from 1-17% (mean 4% across varieties) following modifications in particle bombardment and tissue culture procedures. All plants surviving phosphinothricin selection were screened for uidA and bar gene activity, and for the presence of marker gene sequences by PCR analysis. A minimum of 35% plant 'escape' frequency was achieved with selection on 4 mg l(-1) gluphosinate ammonium after shoot initiation. Mean co-transformation frequency with various genes-of-interest was 66%. The estimated number of insertions of the uidA gene in 25 lines were; 1-2 in 32%, 3-5 in 52%, and 6-8 in 16% of lines. In T(1) progenies, marker genes segregated in a Mendelian fashion in 50% of 39 lines analysed, as determined by transgene activity assays. Based on PCR analysis, it appeared that in some lines the occurrence of distorted segregation was due to poor transmission of the transgenes.

Characterization of monocot and dicot plant S-adenosyl-l-methionine decarboxylase gene families including identification in the mRNA of a highly conserved pair of upstream overlapping open reading frames

S-Adenosyl-L-methionine decarboxylase (AdoMetDC; EC 4.1.1.50) is one of the key regulatory enzymes in the biosynthesis of polyamines. Isolation of genomic and cDNA sequences from rice and Arabidopsis had indicated that this enzyme is encoded by a small multigene family in monocot and dicot plants. Analysis of rice, maize and Arabidopsis AdoMetDC cDNA species revealed that the monocot enzyme possesses an extended C-terminus relative to dicot and human enzymes. Interestingly, we discovered that all expressed plant AdoMetDC mRNA 5' leader sequences contain a highly conserved pair of overlapping upstream open reading frames (uORFs) that overlap by one base. The 5' tiny uORF consists of two or three codons and the 3' small uORF encodes 50-54 residues. Sequences of the small uORFs are highly conserved between monocot, dicot and gymnosperm AdoMetDC mRNA species and the C-terminus of the plant small uORFs is conserved with the C-terminus of nematode AdoMetDC uORFs; such a conserved arrangement is strongly suggestive of a translational regulatory mechanism. No introns were found in the main AdoMetDC proenzyme ORF from any of the plant genes encoding AdoMetDC, whereas introns were found in conserved positions flanking the overlapping uORFs. The absence of the furthest 3' intron from the Arabidopsis gene encoding AdoMetDC2 suggests that this intron was lost recently. Reverse-transcriptase-mediated PCR analysis of the two Arabidopsis genes for AdoMetDC indicated that AdoMetDC1 is abundant and ubiquitous, whereas the gene for AdoMetDC2 is expressed preferentially in leaves and inflorescences. Investigation of recently released Arabidopsis genome sequences has revealed that in addition to the two genes encoding AdoMetDC isolated as part of the present work, four additional genes are present in Arabidopsis but they are probably not expressed.

Poliaminas: Biosíntesis, metabolismo y su papel en la maduración y manipulación postrecolección de frutos / Polyamines: Biosynthesis, metabolism, and their role in ripening and postharvest handling of fruits

Plant polyamines (PAs) are involved in many growth and developmental processes, including several organs such as flowers, leaves and roots. However, behavior of PAs is different in fruits compared with other plant organs. Thus, the concentrations of PAs have been observed to change during development and ripening, though their changing patterns depend on the fruit and the maturity stage. PAs have been related to several types of stress, including, among others, chilling injury, saline stress, modified atmospheres, and mechanical stress. However, whether increased putz-esane concentration is a protective mechanism or whether it is the cause of the stress-induced injury remains unclear. Mechanical stress can be observed in fruits when they are exposed to compression, impact and/or vibration during handling and packaging lines. There is some evidence to support the hypothesis that PAs could also play an important role in this stress; however, there is a lack of information about changes in concentration of endogenous PAs. This paper reviews the role of PAs during some physiological processes affecting fruit ripening and postharvest life. The effects of PAs on the mechanical damages suffered by the fruits during handling, packaging and processing lines are discussed.

Processing of mammalian and plant S-adenosylmethionine decarboxylase proenzymes

S-Adenosylmethionine decarboxylase (AdoMetDC) is a pyruvoyl enzyme, and the pyruvate is formed in an intramolecular reaction that cleaves a proenzyme precursor and converts a serine residue into pyruvate. The wild type potato AdoMetDC proenzyme processed much faster than the human proenzyme and did not require putrescine for an optimal rate of processing despite the presence of three acidic residues (equivalent to Glu11, Glu178, and Glu256) that were demonstrated in previous studies to be required for the putrescine activation of human AdoMetDC proenzyme processing (Stanley, B. A., Shantz, L. M., and Pegg, A. E. (1994) J. Biol. Chem. 269, 7901-7907). A fourth residue that is also needed for the putrescine stimulation of human AdoMetDC proenzyme processing was identified in the present studies, and this residue (Asp174) is not present in the potato sequence. The site of potato AdoMetDC proenzyme processing was found to be Ser73 in the conserved sequence, YVLSESS, which is the equivalent of Ser68 in the human sequence. Replacement of the serine precursor with threonine or cysteine by site-directed mutagenesis in either the potato or the human AdoMetDC proenzyme did not prevent processing but caused a significant reduction in the rate. Although the COOH-terminal regions of the known eukaryotic AdoMetDCs are not conserved, only relatively small truncations of 8 residues from the human protein and 25 residues from the potato proenzyme were compatible with processing. The maximally truncated proteins show no similarity in COOH-terminal amino acid sequence but each contained 46 amino acid residues after the last conserved sequence, suggesting that the length of this section of the protein is essential for maintaining the proenzyme conformation needed for autocatalytic processing.