Overexpression of a heterologous sam gene encoding S-adenosylmethionine synthetase in flax (Linum usitatissimum) cells: Consequences on methylation of lignin precursors and pectins

The Arabidopsis thaliana sam1 gene encoding S-adenosylmethionine synthetase (EC 2.5.1.6) was transferred to flax ( Linum usitatissimum ) cells via Agrobacterium tumefaciens . This enzyme catalyses the conversion of methionine to S-adenosylmethionine (SAM), the major methyl group donor in living cells. The aim of this work was to study the consequences of an increased SAM-synthetase (SAM-S) activity in transgenic cell lines on both the production of mono- and dimethoxylated lignin monomers and the degree of methylesterification of pectins. Hypocotyls were cocultivated with Agrobacterium tumefaciens strain GV3101 (pGV2260) harbouring the pO35SSAM binary vector carrying the sam1 gene under the control of the 35S promoter and the nptII gene for selection of putative transformed cells. Most of the transgenic cell lines exhibited a significant (up to 3.2-fold) increase in SAM-S activity compared to the controls. The results showed that for the cell lines analysed this transformation had no effect on caffeic acid O -methyltransferase (COMT, EC 2.1.1.68) in vitro activity, degree of methoxylation of lignin precursors or lignin deposition, pectin methyltransferase (PMT, EC 2.1.1) in vitro activity, but led to an increase of pectin methylesterification in friable and fast-growing transgenic cell lines.     

Cell differentiation,secondary cell-wall formation and transformation of callus tissue of<Emphasis Type="Italic"> Pinus radiata</Emphasis> D. Don

Tracheid and sclereid differentiation was induced in callus cultures of Pinus radiata D. Don by culturing on a basal medium containing activated charcoal but no phytohormones; sclereids differentiated in callus derived from xylem strips, but not in callus derived from hypocotyl segments. The tracheids differentiated in hypocotyl-derived callus had helical, scalariform, reticulated or pitted secondary cell-wall patterns, but those differentiated in xylem-derived callus had a reticulate or pitted pattern. The thickened tracheid and sclereid walls contained lignin as indicated by the red colour reaction given with phloroglucinol-HCl. The presence of lignin in the cell walls of differentiated callus was confirmed using pyrolysis gas chromatography-mass spectrometry by the detection of phenylpropanoid components derived from lignin. Lignin was also detected using solid-state (13)C cross-polarisation/magic-angle spinning nuclear magnetic resonance spectroscopy and quantified as thioglycolic acid lignin. Monosaccharide analyses of the cell walls isolated from differentiated and undifferentiated calli showed that the cell walls of the differentiated calli contained higher proportions of glucose and mannose, consistent with the presence of greater proportions of gluco- and/or galactogluco-mannans in the secondary cell walls of the differentiated cells. A protocol for the stable transformation of undifferentiated, xylem-derived cultures was successfully developed. Transgenic cell lines were established following Biolistic particle bombardment with a plasmid containing the coding region of the nptII gene and the coding region of the cad gene from P. radiata. Expression of the nptII gene in transgenic lines was confirmed by an NPTII-enzyme-linked immunosorbent assay. The overexpression of cad in the transgenic lines resulted in a down-regulation of cinnamyl alcohol dehydrogenase (EC 1.1.1.195) expression.     

Transgenic maize plants by tissue electroporation.

In this paper, we describe the transformation of regenerable maize tissues by electroporation. In many maize lines, immature zygotic embryos can give rise to embryogenic callus cultures from which plants can be regenerated. Immature zygotic embryos or embryogenic type I calli were wounded either enzymatically or mechanically and subsequently electroporated with a chimeric gene encoding neomycin phosphotransferase (neo). Transformed embryogenic calli were selected from electroporated tissues on kanamycin-containing media and fertile transgenic maize plants were regenerated. The neo gene was transmitted to the progeny of kanamycin-resistant transformants in a Mendelian fashion. This showed that all transformants were nonchimeric, suggesting that transformation and regeneration are a single-cell event. The maize transformation procedure presented here does not require the establishment of genotype-dependent embryogenic type II callus or cell suspension cultures and facilitates the engineering of new traits into agronomically relevant maize inbred lines.     

Induction of anthraquinone biosynthesis in Rubia cordifolia cells by heterologous expression of a calcium-dependent protein kinase gene

Calcium-dependent protein kinases (CDPKs) play an important role in plant cell responses to stress and pathogenic attack. In this study, we investigated the effect of heterologous expression of the Arabidopsis CDPK gene, AtCPK1, on anthraquinone production in transgenic Rubia cordifolia cells. AtCPK1 variants (a constitutively active, Ca(2+) -independent form and a non-active form used as a negative control) were transferred to callus cells by agrobacterial transformation. Overexpression of the constitutively active, Ca(2+) -independent form in R. cordifolia cells caused a 10-fold increase in anthraquinone content compared with non-transformed control cells, while the non-active form of AtCPK1 had no effect on anthraquinone production. Real-time PCR measurements showed that the activation of anthraquinone biosynthesis in transgenic calli correlated with the activation of isochorismate synthase gene expression. The activator effect of AtCPK1 was stable during prolonged periods of transgenic cell cultivation (more than 3 years) and the transgenic cultures exhibited high growth. Our results provide the first evidence that a CDPK gene can be used for the engineering of secondary metabolism in plant cells.     

Fertile transgenic Brachiaria ruziziensis (ruzigrass) plants by particle bombardment of tetraploidized callus

We have produced transgenic plants of the tropical forage crop Brachiaria ruziziensis (ruzigrass) by particle bombardment-mediated transformation of multiple-shoot clumps and embryogenic calli. Cultures of multiple-shoot clumps and embryogenic calli were induced on solidified MS medium supplemented with 0.5mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) and 2mg/L 6-benzylaminopurine (BAP) or 4mg/L 2,4-D and 0.2mg/L BAP, respectively. Both cultures were bombarded with a vector containing an herbicide resistance gene (bar) as a selectable marker and the β-glucuronidase (GUS) reporter gene. Sixteen hours after bombardment, embryogenic calli showed a significantly higher number of transient GUS expression spots per plate and callus than multiple-shoot clumps, suggesting that embryogenic callus is the more suitable target tissue. Following bombardment and selection with 10mg/L bialaphos, herbicide-resistant embryogenic calli regenerated shoots and roots in vitro, and mature transgenic plants have been raised in the greenhouse. Polymerase chain reaction (PCR) and DNA gel blot analysis verified that the GUS gene was integrated into the genome of the two regenerated lines. In SacI digests, the two transgenic lines showed two or five copies of GUS gene fragments, respectively, and integration at different sites. Histochemical analysis revealed stable expression in roots, shoots and inflorescences. Transgenic plants derived from diploid target callus turned out to be sterile, while transgenics from colchicine-tetraploidized callus were fertile.     

A transgenic apple callus showing reduced polyphenol oxidase activity and lower browning potential

Polyphenol oxidase (PPO) is responsible for enzymatic browning of apples. Apples lacking PPO activity might be useful not only for the food industry but also for studies of the metabolism of polyphenols and the function of PPO. Transgenic apple calli were prepared by using Agrobacterium tumefaciens carrying the kanamycin (KM) resistant gene and antisense PPO gene. Four KM-resistant callus lines were obtained from 356 leaf explants. Among these transgenic calli, three calli grew on the medium containing KM at the same rate as non-transgenic callus on the medium without KM. One callus line had an antisense PPO gene, in which the amount and activity of PPO were reduced to half the amount and activity in non-transgenic callus. The browning potential of this line, which was estimated by adding chlorogenic acid, was also half the browning potential of non-transgenic callus.     

Transformation of Maize Cells and Regeneration of Fertile Transgenic Plants

A reproducible system for the generation of fertile, transgenic maize plants has been developed. Cells from embryogenic maize suspension cultures were transformed with the bacterial gene bar using microprojectile bombardment. Transformed calli were selected from the suspension cultures using the herbicide bialaphos. Integration of bar and activity of the enzyme phosphinothricin acetyltransferase (PAT) encoded by bar were confirmed in all bialaphos-resistant callus lines. Fertile transformed maize plants (R0) were regenerated, and of 53 progeny (R1) tested, 29 had PAT activity. All PAT-positive progeny analyzed contained bar. Localized application of herbicide to leaves of bar-transformed R0 and R1 plants resulted in no necrosis, confirming functional activity of PAT in the transgenic plants. Cotransformation experiments were performed using a mixture of two plasmids, one encoding PAT and one containing the nonselected gene encoding [beta]-glucuronidase. R0 plants regenerated from co-transformed callus expressed both genes. These results describe and confirm the development of a system for introduction of DNA into maize.     

The influence of the rolC gene on isoflavonoid production in callus cultures of Maackia amurensis

The polyphenolic complex of Maackia amurensis, as well as a complex of isoflavonoids from M. amurensis callus cultures, display strong hepatoprotective effects in experimental animal and human studies. To increase the yield of polyphenols in cultures of M. amurensis, calli were transformed with the rolC gene as well as with an empty vector that was used as a control. HPLC analysis revealed that the transgenic cultures produced the same complex of isoflavonoids. The complex consisted of 20 compounds, including isoflavones and their glucosides as well as pterocarpans and their glucosides. The cultures transformed with either the empty vector or the rolC gene construct produced on average 1.22 % dry weight (DW) and 1.39 % DW of isoflavonoids, respectively. Isoflavonoid production in the transformed callus lines carrying the empty vector and the rolC gene construct reached 106 and 146 mg/L, respectively. Moreover, the rolC gene construct promoted cell growth and overall cell productivity. The transgenic callus lines expressing the rolC gene exhibited higher levels of the following six isoflavonoids: daidzein, calycosin, formononetin, 4′-Ο-β-glucopyranosyldaidzin, maackiain and 6′-O-malonyl-3-O-β-D-glucopyranosylmaackiain. However, lower levels of genistin were observed in rolC calli than in those carrying the empty vector.     

转AtNHX1基因玉米的产生及其耐盐性分析

以玉米(ZeamaysL.)骨干自交系DH4866、齐319和鲁原16106的胚性愈伤组织为材料,采用农杆菌介导法将AtNHX1和hpt基因转入玉米培养细胞,经筛选获得了抗潮霉素的愈伤组织并再生植株。经PCR检测和Southernblot验证,确定了22.8%的再生植株为转基因植株。农杆菌液浓度、愈伤组织基因型及共培养时间对转化率均有明显影响。外源基因在转基因植株后代中的分离呈多样性,在部分株系中表现出孟德尔遗传规律。耐盐筛选表明,一些转基因植株及其后代具有很好的耐盐性,部分株系可在0.8%-1.0%NaCl溶液浇灌下萌发和生长。Northern杂交表明,植株耐盐性提高与AtNHX1基因的转录水平相一致。     

Rice salT promoter is activated in Papaver somniferum and Nicotiana tabacum transgenic cells in the absence of exogenous ABA

With the aim of modifying secondary metabolism in Opium poppy (Papaver somniferum) and tobacco (Nicotiana tabacum) cells, gene transfer was performed using the sam1 gene from Arabidopsis thaliana under the control of the salT promoter. This promoter is induced by ABA in rice and in tobacco and we have shown that it is also induced in poppy cells (gus gene). Putatively transformed poppy and tobacco cell lines with the sam1 gene were obtained. In the absence of exogenous inducer we noticed the expression of the transgene resulting in a significant increase of SAM-S activity in all tested transformants of poppy and in half the transgenic tobacco cell lines tested. Addition of ABA to the culture medium failed to enhance the expression of the transgene in both species and resulted in a decrease of the sam1 gene expression in some cell lines. Since the salT promoter is induced by exogenous ABA in both species (gus reporter gene), we suggest a partial sam1 transgene inactivation in certain cell lines. These results show that the efficiency of a regulatory sequence may be different when fused with a reporter gene (gus) compared to fusion with a gene belonging to the housekeeping family (sam1).     

转AtNHX1基因玉米的产生及其耐盐性分析

以玉米(Zea mays L.)骨干自交系DH4866、齐319和鲁原16106的胚性愈伤组织为材料,采用农杆菌介导法将AtNHX1和hpt因转入玉米培养细胞,经筛选获得了抗潮霉素的愈伤组织并再生植株.经PCR检测和Southernblot验证,确定了22.8%的再生植株为转基因植株.农杆菌液浓度、愈伤组织基因型及共培养时间对转化率均有明显影响.外源基因在转基因植株后代中的分离呈多样性,在部分株系中表现出孟德尔遗传规律.耐盐筛选表明,一些转基因植株及其后代具有很好的耐盐性,部分株系可在0.8%-1.0%NaCl溶液浇灌下萌发和生长.Northern杂交表明,植株耐盐性提高与AtNHX1基因的转录水平相一致.     

Production of 8-epi-tomentosin by plant cell culture ofXanthium strumarium

This study was conducted to establish a plant cell culture system for the production of medically important secondary metabolites fromXanthium strumarium. The effects of plant growth regulators including NAA, 2,4-D, kinetin, and ABA were examined in terms of callus induction, maintenance of callus and suspension cultures. It was shown that callus was induced upon treatment with NAA while embryo was induced after treatment with 2,4-D. Callus formation was further improved by treatment with ABA and NAA. The level of callusing increased by 17–29% for the seed case, cotyledon, leaf, and hypocotyl and by 96% in the case of the root. Suspension cell lines were established using calli produced from cotyledon, hypocotyl and root and cultured at 25°C under light conditions. The cells grew up to 15 g/L with NAA 2 ppm, BA 2 ppm, and ABA 1 ppm treatment. Supernatants of suspension cultures of cell lines derived from coyledon and hypocotyl produced some distinctive secondary metabolites, one of which was identified as 8-epi-tomentosin, which belongs to the xanthanolides. The amounts of 8-epi-tomentosin produced by the cotyledon-and hypocotylderived cell lines were 13.4 mg/L and 11.0 mg/L, respectively.     

Effect of mouse calcineurin on induction and growth of rice callus transformed by the calcineurin gene

Calcineurin is a Ca²⁺/calmodulin dependent serine/threonine protein phosphatase, and has multiple functions in animal cells. In this work, mouse calcineurin was introduced into wild-type rice and the expression of calcineurin inhibited the induction and growth of rice calli. Inhibitor analysis showed that untransformed and CNAtr transgenic callus cultures had different sensitivity to cyclosporin A (CsA), a specific inhibitor of protein phosphatase calcineurin. When callus cultures were subject to 1 μM of CsA, the growth of calli induced from untransformed wild-type rice was inhibited. Interestingly, the growth inhibition of CNAtr transgenic calli was not detected in presence of 1 μM of CsA. Our findings showed that the heterologous calcineurin might be involved in the regulation of cell growth in plant cells.     

Development of an efficient plant regeneration system for Russian wildrye (<Emphasis Type="Italic">Psathyrostachys juncea</Emphasis>)

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is a cool-season forage grass with a broad adaptation to semi-arid regions of North America. In order to explore the potential of biotechnology for genetic improvement of this important forage species, we developed an efficient tissue culture system. Embryogenic calli were induced from mature embryos with an induction frequency in the range of 2-7%. The selected highly embryogenic calli allowed the regeneration of dozens of plants from a single callus. Individual embryogenic calli were then used to establish single genotype-derived suspension cultures. Eighteen embryogenic cell suspension lines were established from three cultivars (Bozoisky-Select, Sawki and Tetracan). A relatively high green plant regeneration frequency, up to 70%, was achieved from plated cell clusters of the established suspension cultures. The regenerated plants were fertile after two winters of vernalization in the field. This efficient plant regeneration system provides a solid basis for generating transgenic plants.     

Effective selection of transgenic papaya plants with the PMI/Man selection system

The selectable marker gene phospho-mannose isomerase (pmi), which encodes the enzyme phospho-mannose isomerase (PMI) to enable selection of transformed cell lines on media containing mannose (Man), was evaluated for genetic transformation of papaya (Carica papaya L.). We found that papaya embryogenic calli have little or no PMI activity and cannot utilize Man as a carbon source; however, when calli were transformed with a pmi gene, the PMI activity was greatly increased and they could utilize Man as efficiently as sucrose. Plants regenerated from selected callus lines also exhibited PMI activity but at a lower specific activity level. Our transformation efficiency with Man selection was higher than that reported using antibiotic selection or with a visual marker. For papaya, the PMI/Man selection system for producing transgenic plants is a highly efficient addition to previously published methods for selection and may facilitate the stacking of multiple transgenes of interest. Additionally, since the PMI/Man selection system does not involve antibiotic or herbicide resistance genes, its use might reduce environmental concerns about the potential flow of those genes into related plant populations.     

Generation and properties of ascorbic acid-deficient transgenic tobacco cells expressing antisense RNA for L-galactono-1,4-lactone dehydrogenase

In higher plants, the terminal step of L-ascorbic acid (AsA) biosynthesis is catalyzed by the enzyme L-galactono-1,4-lactone dehydrogenase (EC 1.3.2.3, GalLDH). We generated AsA-deficient transgenic tobacco BY-2 cell lines by antisense expression of the GalLDH cDNA that was amplified from BY-2 cells using PCR. Two transgenic cell-lines, AS1-1 and AS2-2, having a marked expression of antisense RNA were analyzed. Antisense suppression of GalLDH mRNA led to a significant decline in the GalLDH activity. The AsA levels in the transgenic cell lines were found to be 30% lower than the wild-type BY-2 cells. In synchronous cultures, division of AS1-1 and AS2-2 cells was restrained with a concomitant decrease in mitotic index that was probably due to a decline in AsA levels. The rate of cell growth was also found to be less than that of the wild-type cells. Interestingly, there was a significant phenotypic difference between the transgenic and wild-type cells. The calli of AS1-1 and AS2-2 appeared to be sticky and soft. Back extrusion method also showed that AsA-deficient BY-2 callus was rheologically soft. Furthermore, microscopic analysis revealed that AS1-1 and AS2-2 cells were abnormally slender, suggesting a potential for a significant and a uni-axial elongation. Thus, we observed that decline in the AsA levels has an adverse effect on the division, growth and structure of a plant cell.     

Control of the glutathione S-transferase and mas1' promoter-driven GUS activity in auxin heterotrophic and autotrophic tobacco calli by exogenous 2,4-d-induced ethylene

Auxin autotrophic and heterotrophic lines of tobacco calli may differ not only in their indoleacetic acid (IAA) synthetizing abilities and sensitivities to exogenous auxins, but also in their gene expression patterns. Auxin autotrophic callus tissues from the leaf protoplasts of transgenic Nicotiana tabacum SR1 plants involving mas1′::GUS gene fusion were generated and the growth of cultures was compared with that of the heterotrophic lines of the same transgenic tissues on MS medium containing different concentrations of IAA or 2,4‐d . The mas1′::GUS gene fusion expression was investigated, together with the glutathione S‐transferase activities (GST, EC 2.5.1.18) in auxin autotrophic and heterotrophic tobacco calli. Both the mas1′ promoter and GST gene promoters contain ocs or ocs‐like elements, responsible for both auxin and ethylene/wound inducibility. The mas1′ promoter exhibited a much higher expression activity in the heterotrophic cultures growing on IAA than in the autotrophic ones, but in contrast with the natural auxin, the mas1′::GUS activity decreased at elevated 2,4‐d concentrations in the heterotrophic tissues and increased with increasing 2,4‐d concentrations in the autotrophic lines. The induction of GST activity by different exogenous auxin concentrations was much higher in the autotrophic lines, especially in the case of 2,4‐d . Higher concentrations of external 2,4‐d resulted in increased ethylene production, which displayed different kinetics in the two types of calli. The ethylene‐inducing 2,4‐d concentrations increased the growth of the heterotrophic, but decreased that of the autotrophic lines. Blocking the ethylene receptors and hence the signal perception by 2,5‐norbornadiene (NBD) in the heterotrophic tissues increased the 2,4‐d ‐induced mas1′ promoter and GST activities, suggesting that the gaseous hormone counteracted the auxin response pathway. This was not found in the autotrophic tissues, where NBD decreased the mas1′‐driven GUS activity. The GST activities were slightly decreased, or almost independent of the action of ethylene. It is suggested that the cross‐talk between the auxin‐ and ethylene‐induced signal transduction pathways may differ in the auxin autotrophic and heterotrophic lines.     

Effect of hydropriming on Trigonella foenum callus growth,biochemical traits and phytochemical components under PEG treatment

The induction of secondary metabolites under osmotic stress is well documented. However, cell death is probably due to osmotic stress. This work tries to study the synergetic effect of hydropriming and polyethylene glycol (PEG) on enhancing the secondary metabolites production in fenugreek callus cultures without facing cell death. PEG initiates the stress and the hydropriming increase the plant cell response against the stress. Fenugreek calli were initiated from hypocotyl of two groups of seeds, the first was hydroprimed overnight before germination, the second remained dry. Three months old calli of the two groups were subcultured on media containing two different concentration of PEG (5, 10%). The calli growth, biochemical analysis, secondary metabolism keys, and secondary metabolites were determined after 4 weeks. PE induced oxidative stress, which increased the membrane lipid peroxidation and decreased cell viability and growth. Hydropriming enhanced the activity of antioxidant enzymes, regulating the reactive oxygen species level, accumulating the osmolytes and secondary products. Therefore the primed callus can tolerate the osmotic stress initiated with PEG. Consequently, cell biomass increased and not affected by PEG treatment. On the other hand, the calli from non-primed seeds have a significant decrease in fresh weight, and dry weight under the higher PEG treatment. The hydropriming protected the growth of the cells under PEG treatment with a high content of secondary metabolites and high antioxidant machinery. The synergetic effect of hydropriming and PEG can be used as a simple and low-cost way to produce valuable compounds in commercial industrial bioreactors.