Simultaneous reduction of the activity of two related enzymes, involved in early steps of the polyamine biosynthetic pathway, by a single antisense cDNA in transgenic rice

Spermine facilitates recovery from drought but does not confer drought tolerance in transgenic rice plants expressing Datura stramonium S-adenosylmethionine decarboxylase

Polyamines are known to play important roles in plant stress tolerance but it has been difficult to determine precise functions for each type of polyamine and their interrelationships. To dissect the roles of putrescine from the higher polyamines spermidine and spermine, we generated transgenic rice plants constitutively expressing a heterologous S-adenosylmethionine decarboxylase (SAMDC) gene from Datura stramonium so that spermidine and spermine levels could be investigated while maintaining a constant putrescine pool. Whereas transgenic plants expressing arginine decarboxylase (ADC) produced higher levels of putrescine, spermidine and spermine, and were protected from drought stress, transgenic plants expressing SAMDC produced normal levels of putrescine and showed drought symptoms typical of wild type plants under stress, but the transgenic plants showed a much more robust recovery on return to normal conditions (90% full recovery compared to 25% partial recovery for wild type plants). At the molecular level, both wild type and transgenic plants showed transient reductions in the levels of endogenous ADC1 and SAMDC mRNA, but only wild type plants showed a spike in putrescine levels under stress. In transgenic plants, there was no spike in putrescine but a smooth increase in spermine levels at the expense of spermidine. These results confirm and extend the threshold model for polyamine activity in drought stress, and attribute individual roles to putrescine, spermidine and spermine.

Increased spermine oxidase (SMO) activity as a novel differentiation marker of myogenic C2C12 cells

Spermine oxidase (SMO) is a FAD-containing enzyme involved in animal cell polyamines (PA) homeostasis, selectively active on spermine and producing H(2)O(2), spermidine, and the 3-aminopropanal. In the present study, we have examined the SMO gene expression during the mouse myoblast C2C12 cell differentiation induced with two different stimuli by RT-PCR analysis, polysome-mRNP distribution and enzyme activity. SMO transcript accumulation and enzymatic activity increases during C2C12 cell differentiation and correlates with the decrease of spermine content. Many proteins are highly regulated during the phenotypic conversion of rapidly dividing C2C12 myoblasts into fully differentiated post-mitotic myotubes. The SMO gene induction represents a novel and additional marker of C2C12 cell differentiation. The sub-cellular localization of the SMOalpha and SMOmu splice variants is not involved in the differentiation processes. Nuclear localization of only the SMOmu protein was confirmed.

Characterization of spermidine and spermine synthases in Lotus japonicus: induction and spatial organization of polyamine biosynthesis in nitrogen fixing nodules

The biosynthesis of the polyamines spermidine (Spd) and spermine (Spm) from putrescine (Put) is catalysed by the consequent action of two aminopropyltransferases, spermidine synthase (SPDS EC: 2.5.1.16) and spermine synthase (SPMS EC: 2.5.1.22). Two cDNA clones coding for SPDS and SPMS homologues in the nitrogen-fixing nodules of the model legume Lotus japonicus were identified. Functionality of the encoded polypeptides was confirmed by their ability to complement spermidine and spermine deficiencies in yeast. The temporal and spatial expression pattern of the respective genes was correlated with the accumulation of total polyamines in symbiotic and non-symbiotic organs. Expression of both genes was maximal at early stages of nodule development, while at later stages the levels of both transcripts declined. Both genes were expressed in nodule inner cortical cells, vascular bundles, and central tissue. In contrast to gene expression, increasing amounts of Put, Spd, and Spm were found to accumulate during nodule development and after maturity. Interestingly, nodulated plants exhibited systemic changes in both LjSPDS and LjSPMS transcript levels and polyamine content in roots, stem and leaves, in comparison to uninoculated plants. These results give new insights into the neglected role of polyamines during nodule development and symbiotic nitrogen fixation (SNF).

Expression of an antisense Datura stramonium S-adenosylmethionine decarboxylase cDNA in tobacco: changes in enzyme activity, putrescine-spermidine ratio, rhizogenic potential, and response to methyl jasmonate

S-adenosylmethionine decarboxylase activity (SAMDC; EC 4.1.1.21) leads to spermidine and spermine synthesis through specific synthases which use putrescine, spermidine and decarboxylated S-adenosylmethionine as substrates. In order to better understand the regulation of polyamine (PA), namely spermidine and spermine, biosynthesis, a SAMDC cDNA of Datura stramonium was introduced in tobacco (Nicotiana tabacum L. cv. Xanthi) in antisense orientation under the CaMV 35S promoter, by means of Agrobacterium tumefaciens and leaf disc transformation. The effect of the genetic manipulation on PA metabolism, ethylene production and plant morphology was analysed in primary transformants (R0), and in the transgenic progeny (second generation, R1) of self-fertilised primary transformants, relative to empty vector-transformed (pBin19) and wild-type (WT) controls. All were maintained in vitro by micropropagation. Primary transformants, which were confirmed by Southern and northern analyses, efficiently transcribed the antisense SAMDC gene, but SAMDC activity and PA titres did not change. By contrast, in most transgenic R1 shoots, SAMDC activity was remarkably lower than in controls, and the putrescine-to-spermidine ratio was altered, mainly due to increased putrescine, even though putrescine oxidising activity (diamine oxidase, EC 1.4.3.6) did not change relative to controls. Despite the reduction in SAMDC activity, the production of ethylene, which shares with PAs the common precursor SAM, was not influenced by the foreign gene. Some plants were transferred to pots and acclimatised in a growth chamber. In these in vivo-grown second generation transgenic plants, at the vegetative stage, SAMDC activity was scarcely reduced, and PA titres did not change. Finally, the rhizogenic potential of in vitro-cultured leaf explants excised from antisense plants was significantly diminished as compared with WT ones, and the response to methyl jasmonate, a stress-mimicking compound, in terms of PA conjugation, was higher and differentially affected in transgenic leaf discs relative to WT ones. The effects of SAMDC manipulation are discussed in relation to plant generation, culture conditions and response to stress.

Immunomodulation of polyamine biosynthesis in tobacco plants has a significant impact on polyamine levels and generates a dwarf phenotype

Ornithine decarboxylase (ODC) is a cytosolic enzyme that catalyses the direct decarboxylation of l-ornithine to putrescine, one of the rate-limiting steps of polyamine biosynthesis in plants. In the present study, an ODC-specific murine single-chain antibody fragment (scFvODC1) was generated by phage display technology. To evaluate the effect of the recombinant antibody fragment on ODC activity and polyamine levels, we produced transgenic tobacco plants that accumulated scFvODC1 in the cytosol. Expression levels of up to 4% total soluble protein (TSP) were achieved, resulting in the inhibition of up to 90% of endogenous ODC activity. A significant reduction in putrescine, spermidine and spermine levels was observed in transgenic lines producing high levels of scFvODC1. Furthermore, these lines showed developmental abnormalities and a dwarf phenotype. We show that the immunomodulation of enzyme activity is a powerful approach that can be used to alter complex and tightly controlled metabolic pathways, allowing specific steps in the pathway to be blocked and the resulting physiological effects to be investigated.

Induction and spatial organization of polyamine biosynthesis during nodule development in Lotus japonicus

Putrescine and other polyamines are produced by two alternative pathways in plants. One pathway starts with the enzyme arginine decarboxylase (ADC; EC 4.1.1.19), the other with ornithine decarboxylase (ODC; EC 4.1.1.17). Metabolite profiling of nitrogen-fixing Lotus japonicus nodules, using gas chromatography coupled to mass spectrometry, revealed a two- to sixfold increase in putrescine levels in mature nodules compared with other organs. Genes involved in polyamine biosynthesis in L japonicus nodules were identified by isolating cDNA clones encoding ADC (LjADC1) and ODC (LjODC) from a nodule library. Searches of the public expressed sequence tag databases revealed the presence of a second gene encoding ADC (LjADC2). Real-time reverse-transcription-polymerase chain reaction analysis showed that LjADC1 and LjADC2 were expressed throughout the plant, while LjODC transcripts were detected only in nodules and roots. Induction of LjODC and LjADC gene expression during nodule development preceded symbiotic nitrogen fixation. Transcripts accumulation was maximal at 10 days postinfection, when a 6.5-fold increase in the transcript levels of LjODC was observed in comparison with the uninfected roots, while a twofold increase in the transcript levels of LjADC1 and LjADC2 was detected. At later stages of nodule development, transcripts for ADC drastically declined, while in the case of ODC, transcript accumulation was higher than that in roots until after 21 days postinfection. The expression profile of genes involved in putrescine biosynthesis correlated well with the expression patterns of genes involved in cell division and expansion, including a L. japonicus Cyclin D3 and an alpha-expansin gene. Spatial localization of LjODC and LjADC1 gene transcripts in developing nodules revealed that both transcripts were expressed in nodule inner cortical cells and in the central tissue. High levels of LjADC1 transcripts were also observed in both nodule and connecting root vascular tissue, suggesting that putrescine and other polyamines may be subject to long-distance transport. Our results indicate that polyamines are primarily involved in physiological and cellular processes involved in nodule development, rather than in processes that support directly symbiotic nitrogen fixation and assimilation.

Ornithine decarboxylase, polyamines and CD11b expression in HL-60 cells during differentiation induced by retinoic acid

Polyamines (PA) and retinoic acid affect mammalian cell growth, differentiation and apoptosis. Retinoic acid induces granulocytic differentiation of mieloid cell lines and, during this process, is responsible for the expression of CD11b, a surface antigen. In this study we investigate the effects of retinoic acid on HL-60 cells, monitoring ornithine decarboxylase (ODC) activity (enzyme rate of PA), putrescine (PUT), spermidine (SPD), spermine (SPM) levels, CD11b myeloid surface marker differentiation, cell cycle, and apoptosis. ODC activity and PUT levels are correlated with mieloid cell differentiation induced by retinoic acid treatment. Only the ODC/PUT ratio is connected with retinoic acid treated HL-60 cells. Treated cultures show a decrease of proliferation and a cell block in the G0/G1 phase, with consequent diminished S phase. The G0/G1 and S phases are significantly related to ODC activity and to PUT and SPD behavior, whereas in differentiating condition only the decrease of PUT is related to the S phase. CD11b expression, stimulated by retinoic acid treatment, is associated with the SPM trend. Total PA behavior agrees with apoptotic cell increase after 96 h of stimulation. Our data show that retinoic acid treatment modifies ODC activity and the turnover of PA. PUT, SPD and SPM, therefore, have a different role, and may be involved in the differentiative/apoptotic program of retinoic acid treated HL-60 cells.

Effect of reduced arginine decarboxylase activity on salt tolerance and on polyamine formation during salt stress in Arabidopsis thaliana

Polyamines have been suggested to play an important role in stress protection. However, attempts to determine the function of polyamines have been complicated by the fact that, dependent on the conditions, polyamine contents increase or decrease during stress. To determine the importance of polyamine formation during salt stress, we analysed polyamine contents and salt tolerance in two Arabidopsis thaliana mutants, spe1-1 and spe2-1 (Watson et al. Plant J 13: 231-239, 1998), with reduced activity of arginine decarboxylase (EC 4.1.1.19), an important enzyme in polyamine synthesis. Polyamines accumulated in wild-type plants (Col-0 and Ler-0) that were pre-treated with 100 mM NaCl before transfer to 125 mM NaCl, but not in plants that were directly transferred to 125 mM NaCl without prior treatment with 100 mM NaCl. This shows that polyamine accumulation depends on acclimation to salinity. The salt treatment that induced polyamine accumulation in wild-type plants did not lead to polyamine accumulation in the spe1-1 and spe2-1 mutants. Decreased fresh weight, chlorophyll content and photosynthetic efficiency indicated that the spe1-1 mutant was more severely affected by salt stress than its wild type, Col-0. In the spe2-1 mutant decreased salt tolerance compared to its wild type, Ler-0, became apparent as bleaching under severe salt stress. The present results demonstrate that decreased polyamine formation due to lower arginine decarboxylase activity leads to reduced salt tolerance.

Ectopic expression of maize polyamine oxidase and pea copper amine oxidase in the cell wall of tobacco plants

To test the feasibility of altering polyamine levels by influencing their catabolic pathway, we obtained transgenic tobacco (Nicotiana tabacum) plants constitutively expressing either maize (Zea mays) polyamine oxidase (MPAO) or pea (Pisum sativum) copper amine oxidase (PCuAO), two extracellular and H(2)O(2)-producing enzymes. Despite the high expression levels of the transgenes in the extracellular space, the amount of free polyamines in the homozygous transgenic plants was similar to that in the wild-type ones, suggesting either a tight regulation of polyamine levels or a different compartmentalization of the two recombinant proteins and the bulk amount of endogenous polyamines. Furthermore, no change in lignification levels and plant morphology was observed in the transgenic plants compared to untransformed plants, while a small but significant change in reactive oxygen species-scavenging capacity was verified. Both the MPAO and the PCuAO tobacco transgenic plants produced high amounts of H(2)O(2) only in the presence of exogenously added enzyme substrates. These observations provided evidence for the limiting amount of freely available polyamines in the extracellular space in tobacco plants under physiological conditions, which was further confirmed for untransformed maize and pea plants. The amount of H(2)O(2) produced by exogenously added polyamines in cell suspensions from the MPAO transgenic plants was sufficient to induce programmed cell death, which was sensitive to catalase treatment and required gene expression and caspase-like activity. The MPAO and PCuAO transgenic plants represent excellent tools to study polyamine secretion and conjugation in the extracellular space, as well as to determine when and how polyamine catabolism actually intervenes both in cell wall development and in response to stress.

Expression of a heterologous S-adenosylmethionine decarboxylase cDNA in plants demonstrates that changes in S-adenosyl-L-methionine decarboxylase activity determine levels of the higher polyamines spermidine and spermine

We posed the question of whether steady-state levels of the higher polyamines spermidine and spermine in plants can be influenced by overexpression of a heterologous cDNA involved in the later steps of the pathway, in the absence of any further manipulation of the two synthases that are also involved in their biosynthesis. Transgenic rice (Oryza sativa) plants engineered with the heterologous Datura stramonium S-adenosylmethionine decarboxylase (samdc) cDNA exhibited accumulation of the transgene steady-state mRNA. Transgene expression did not affect expression of the orthologous samdc gene. Significant increases in SAMDC activity translated to a direct increase in the level of spermidine, but not spermine, in leaves. Seeds recovered from a number of plants exhibited significant increases in spermidine and spermine levels. We demonstrate that overexpression of the D. stramonium samdc cDNA in transgenic rice is sufficient for accumulation of spermidine in leaves and spermidine and spermine in seeds. These findings suggest that increases in enzyme activity in one of the two components of the later parts of the pathway leading to the higher polyamines is sufficient to alter their levels mostly in seeds and, to some extent, in vegetative tissue such as leaves. Implications of our results on the design of rational approaches for the modulation of the polyamine pathway in plants are discussed in the general framework of metabolic pathway engineering.