Gene stability in transgenic aspen (Populus). I. Flanking DNA sequences and T-DNA structure

The stability of transgenes in the genome of transformed plants depends strongly on their correct physical integration into the host genome as well as on flanking target DNA sequences. For long-lived species like trees, however, no information is available so far concerning inactivation or loss of transgenes due to gene silencing or somatic genome rearrangement events. In this study, four independently transformed 35S-rolC transgenic hybrid aspen plants (Populus tremula L. x tremuloides Michx.), each harbouring one copy of the transgene, were investigated during continuous growth in the greenhouse. In one of these transgenic lines (Esch5:35S-rolC-#1) individuals frequently show phenotypic reversions, while in the remaining three lines (Esch5:35S-rolC-#3, -#5, -#16) the gene was essentially stable. Molecular analysis including PCR, Southern and Northern assays clearly showed that the transgene had been lost in the revertant tissue of the unstable line. Sequencing of T-DNA right and left borders, and flanking DNA regions, in all four transgenic aspen lines revealed no differences either in the type of flanking DNA (G-C to A-T ratio) or with respect to the presence of enhancers or MAR (matrix associated repeats)-like structures. Primers located within the left and right flanking regions in the three stable lines could be used to recover the target sites from the untransformed plants. This was not possible, however, with the unstable line, indicating that at least one flanking sequence does not derive from the plant target DNA but is of unknown origin. PCR using other primer pairs, and inverse PCR analysis, revealed an additional truncated T-DNA copy of 1050 nucleotides adjacent to the left border of the complete copy in this line. Sequencing of this truncated T-DNA revealed that it represented an inverted copy of part of the right half of the original construct. This special feature would allow the inverted repeat to pair with right border sequences of the complete copy. This would explain the frequently observed reversion resulting in transgene loss as due to intrachromosomal base-pairing leading to double-stranded loops of single-stranded DNA during mitotic cell divisions.

Degradation of rutin by Aspergillus flavus. Purification and characterization of rutinase

Aspergillus flavus produces an adaptive glycosidase (rutinase) that hydrolyzes rutin to quercetin and rutinose. Production of rutinase occurs when the mold is grown on the glycosides rutin, hyperosid, and naringin, and on the aglycones quercetin, kaempferol, rhamnetin, 2,4-dihydroxybenzoic acid, and 3,4-dihydroxyphenylacetic acid, but not when grown on glucose, galactose, rhamnose, or rutinose. Rutinase, after partial purification, is relatively stable when stored at −20 °C, and is most stable and most active at pH 5.6. The enzyme is quite specific, hydrolyzing the 5-glucoside of sakuranetin, the 3-rutinoside and 3-galactoside of quercetin, but not the 3-L-rhamnoside nor any of the common glycosides. The hydrolysis of rutin is carried to completion aided by the insolubility of the aglycone quercetin in water.

Fractionation of beta-glucosidases and related extracellular enzymes from Aspergillus niger

Industrial concentrates from Aspergillus niger culture filtrates were fractionated by ion-exchange and adsorption chromatography. Several other types of hydrolases were completely removed. Eight partially purified components were obtained. Using specific activity as an estimate of purification, one aryl-beta-glucosidase was purified 35-fold. Another component showed 147-fold purification using a viscosimetric assay with carboxymethylcellulose as substrate. The aryl-beta-glucosidase was distinctly more thermolabile than the carboxymethylcellulase.

Effect of storage time and dietary enzyme on the metabolizable energy and digesta viscosity of barley-based diets for poultry

The effect of barley storage time and dietary enzyme addition on the energy value of barley-based broiler diets was studied in two experiments. A two-rowed winter barley (Beka cultivar) was stored at room temperature for 0, 3, 6, 16, and 32 wk after harvesting. At these dates, diets were formulated using 50% barley with and without the addition of a commercial beta-glucanase-based enzyme product. In Experiment 1, 320 Arbor Acres chickens (eight replicates of three 10-d-old birds and eight replicates of one 30-d-old bird, per treatment) were fed the experimental diets to determine the AMEn following a 2 x 2 x 5 (age by enzyme by barley storage time) factorial design. At the end of the metabolism trial, viscosity of the intestinal contents was determined in 30-d-old broilers. Total beta-glucan, nonstarch polysaccharides (NSP), in vitro viscosity, and endogenous enzyme activity of barley grain decreased with increasing storage time. Dietary AMEn increased with barley storage time (from 2,755 to 2,939 kcal/kg DM, P < 0.001, for 0 and 32 wk of storage, respectively), with enzyme addition (2,861 vs 2,919 kcal/kg DM, P < 0.003), and with the age of animals (2,826 and 2,958 kcal/kg DM for 10- and 30-d-old chickens, respectively, P < 0.001). Interactions of enzyme and age by barley storage time (P < 0.02 and P < 0.001, respectively) were also detected. These data indicate that the minimum time of barley storage before its inclusion in broiler feed depends on the animals' age (more than 6 wk for 10-d-old chickens and 3 wk for 30-d-old chickens), and that the use of enzymes allowed a reduction in the time of barley storage. Digesta viscosity decreased with barley storage time (P < 0.001), and with enzyme addition (P < 0.001), an interaction of storage time by enzyme addition was shown (P < 0.007). Digesta viscosity was also negatively related to the dietary AMEn content (r = -0.68, P < 0.01). In vitro barley viscosity explained 53 and 90% of the variation in gut viscosity produced by unsupplemented and enzyme supplemented diets, respectively. In Experiment 2, the same diets as Experiment 1 and the barley grain were intubated into 120 adult roosters (Hy-Line) to determine TMEn. Dietary and barley TMEn values were not affected by barley storage time or enzyme addition (3,237 and 3,037 kcal TMEn/kg DM for diets and barley, respectively).

Pattern of DNA binding of nuclear proteins to the proximal Agrobacterium rhizogenes rolC promoter is altered during somatic embryogenesis of carrot

Carrot cells cultured in vitro in a medium supplemented with 2,4-D (2,4-dichlorophenoxyacetic acid) proliferate as unorganized cell clusters. Upon removal of 2,4-D from the culture medium, these cells undergo somatic embryo formation through globular, heart, and torpedo stages. Since the proximal -255 bp upstream region of the rolC gene of the Ri plasmid confers somatic embryogenesis-related activation on the uidA gene in transgenic carrot cell culture, we investigated the interaction of nuclear proteins with the proximal -255bp upstream sequences to characterize the mechanism of somatic embryogenesis-related activation. Gel retardation experiments revealed that there were several different profiles of the relative levels of DNA binding activities in nuclear protein extracts from calli, PEMs (proembryogenic masses), globular embryos, and heart/torpedo embryos. The binding activity associated with a fragment (-203 bp to -92 bp) of one protein (BI) was most abundant in globular embryos. Another DNA binding protein (AII) showed the highest DNA binding activity in calli, but had low binding activities in PEMs and globular embryos. Such an altered pattern of DNA binding activities of nuclear proteins may contribute to somatic embryogenesis-related activation of the rolC promoter. Competition experiments with oligonucleotides revealed that the BI protein interacts with AT-rich sequences.

Excision of the maize transposable element Ac in periclinal chimeric leaves of 35S-Ac-rolC transgenic aspen-Populus

The transposable element Ac from maize, in combination with the phenotypic selectable marker rolC, was employed in transformation experiments of a hybrid aspen clone. A number of transgenic clones exhibited light-green sectors on green leaves. In vitro regeneration from leaves showing a high number of light-green spots resulted in R2 plants, which also showed light-green sectored leaves. However, only one out of 385 regenerated plants obtained showed green leaves. Both PCR and northern analysis indicated Ac excision and restoration of rolC expression. In Southern blot analysis of this green plant additional bands were observed as compared to the original R1 plant. The occurrence of these bands and a suggested Ac excision in the non-green L1-epidermal layer leading to periclinal chimerism of this plant is discussed.

Expression patterns of vascular-specific promoters RolC and Sh in transgenic potatoes and their use in engineering PLRV-resistant plants

The expression patterns of GUS fusion constructs driven by the Agrobacterium rhizogenes RolC and the maize Sh (Shrunken; sucrose synthase-1) promoters were examined in transgenic potatoes (cv. Atlantic). RolC drove high-level gene expression in phloem tissue, bundle sheath cells and vascular parenchyma, but not in xylem or non-vascular tissues. Sh expression was exclusively confined to phloem tissue. Potato leafroll luteovirus (PLRV) replicates only in phloem tissues, and we show that when RolC is used to drive expression of the PLRV coat protein gene, virus-resistant lines can be obtained. In contrast, no significant resistance was observed when the Sh promoter was used.

AN INDUCIBLE SYSTEM FOR THE HYDROLYSIS AND TRANSPORT OF BETA-GLUCOSIDES IN YEAST. I. CHARACTERISTICS OF THE BETA-GLUCOSIDASE ACTIVITY OF INTACT AND OF LYSED CELLS

A strain of bakers' yeast was isolated which could utilize cellobiose and other β-D-glucosides quantitatively as carbon and energy sources for growth. Cellobiose-grown cells contained a largely cryptic enzyme active against the chromogenic substrate p-nitrophenyl-β-D-glucoside. The patent (intact cell) activity of such cells was inhibited by azide and, competitively, by cellobiose; neither agent inhibited the β-glucosidase activity of lysed cells or of extracts. The enzyme induced by growth in cellobiose medium had no affinity for cellobiose as either substrate or inhibitor; its substrate specificity classifies it as an aryl-β-glucosidase. It was concluded that growth in cellobiose also induced the formation of a stereospecific and energy-dependent system whose function determined the rate at which intact cells could hydrolyze substrates of the intracellular β-glucosidase.

BETA-GLUCOSIDASE SYSTEM OF NEUROSPORA CRASSA. I. BETA-GLUCOSIDASE AND CELLULASE ACTIVITIES OF MUTANT AND WILD-TYPE STRAINS

Eberhart, Bruce (University of North Carolina, Greensboro), David F. Cross, and Lewis R. Chase. beta-Glucosidase system of Neuspora crassa. I. beta-Glucosidase and cellulose activities of mutant and wild-type strains. J. Bacteriol. 87:761-770. 1964.-A mutant strain, gluc-1, of Neurospora crassa was isolated and characterized by its low level of beta-glucosidase activity. The mutant was selected by testing irradiated colonies for extracellular beta-glucosidase activity. Strains containing the gluc-1 gene were also visibly detected by their reduced ability to destroy esculin in their growth media. The mutant strain grew at wild-type rates with cellobiose or carboxymethylcellulose as carbon sources. This auxotrophic similarity with wild type is explained by the presence of at least two beta-glucosidases (and possibly two cellulases) in Neurospora that act complementarily. The thermolabile beta-glucosidase was destroyed after 1 min of incubation at 60 C. This enzyme was present in mycelia but absent in conidial extracts. A second beta-glucosidase that is comparatively stable at 60 C was present in both mycelia and conidia. A partial separation of these enzymes was achieved with ammonium fractionation of mycelial extracts of gluc-1 and wild-type strains. Thermolabile beta-glucosidase and cellulase activity appear not to be affected by the gluc-1 mutation, whereas the thermostable glucosidase is greatly reduced in gluc-1 strains.

Expression of two heterologous promoters, Agrobacterium rhizogenes rolC and cauliflower mosaic virus 35S, in the stem of transgenic hybrid aspen plants during the annual cycle of growth and dormancy

We monitored, for the first time, the activity of two model heterologous promoters, the Agrobacterium rhizogenes rolC and the cauliflower mosaic virus (CaMV) 35S, throughout the annual cycle of growth and dormancy in a perennial species, hybrid aspen. Each promoter was fused to the uidA beta-glucuronidase (GUS) reporter gene and the constructs were introduced into the hybrid aspen genome by Agrobacterium-mediated transformation. Both wild-type and transgenic plants were cultivated under different regimes of photoperiod and temperature to induce passage through one growth-dormancy-reactivation cycle, and at intervals GUS staining was assessed in stem sections. In rolC::uidA transformants, GUS activity in rapidly growing current-year shoots was not only tissue-specific, being localized to the phloem, but also cell-specific at the shoot base, where it was present only in the companion cells. However, during the onset of dormancy induced by short photoperiod, GUS activity shifted laterally from the phloem to include the cortex and pith. After subsequent exposure to chilling temperatures to induce the transition between the dormancy stages of rest and quiescence, GUS activity almost disappeared from all stem tissues, but regained its original phloem specificity and intensity after the shoots were reactivated by exposing them to long photoperiod and high temperatures. In contrast, GUS activity in the stem of 35S::uidA transformants was strong in all tissues except for the vascular cambium and xylem, and did not vary in intensity during the growth-dormancy-reactivation cycle. The lateral shift and increased intensity of GUS activity in the stem of rolC::uidA transformants during dormancy induction was shown to be associated with the accumulation of starch, and to be mimicked by incubating stem sections in sucrose, as well as glucose and fructose, but not sorbitol, prior to the GUS assay. Our results demonstrate that the activities of the rolC and 35S promoters varied in very different, unpredictable ways during the annual cycle of growth and dormancy in a perennial species, and indicate that the spatial and temporal variation in rolC promoter activity that we observed in the stem of transgenic hybrid aspen plants is attributable to cellular and seasonal changes in sucrose content.

Neuritogenic effect of natural iridoid compounds on PC12h cells and its possible relation to signaling protein kinases

We examined effect of iridoid glucosides, aucubin, catalpol, geniposide and gardenoside, and their enzymic hydrolysates on neurite outgrowth of PC12h cells. Except for aucubin, these glucosides induced neurite outgrowth at 0.1 microgram/ml and above in medium after 3 d of treatment. Hydrolysates of the four glucosides all caused neuritogenesis. Geniposide hydrolysate enhanced responses of cells to carbachol and KCl-induced depolarization in terms of cytoplasmic free-calcium concentration. The aglucone of geniposide, genipin, also promoted neurite outgrowth in a dose-dependent manner (ED50 = 0.7 microM). The neuritogenic effect of genipin was partially or considerably inhibited in the presence of H-89 and genistein. All the results presented suggest that certain iridoid compounds can induce neuronal differentiation in PC12h cells through activation of components of the intracellular signal transduction pathway.

Retention of Saccharomyces cerevisiae cell wall proteins through a phosphodiester-linked beta-1,3-/beta-1,6-glucan heteropolymer

Yeast cell wall proteins, including Cwp1p and alpha-agglutinin, could be released by treating the cell wall with either beta-1,3-or beta-1,6-glucanases, indicating that both polymers are involved in anchoring cell wall proteins. It was shown immunologically that both beta-1,3- and beta-1,6-glucan were linked to yeast cell wall proteins, including Cwp1p and alpha-agglutinin. It was further shown that beta-1,3-glucan was linked to the wall protein through a beta-1,6-glucan moiety. The beta-1,6-glucan moiety could be removed from Cwp1p and other cell wall proteins by cleaving phosphodiester bridges either enzymatically using phosphodiesterases or chemically using ice-cold aqueous hydrofluoric acid. These observations are consistent with the notion that cell wall proteins in Saccharomyces cerevisiae are linked to a beta-1,3-/beta-1,6-glucan heteropolymer through a phosphodiester linkage and that this polymer is responsible for anchoring cell wall proteins. It is proposed that this polymer is identical to the alkali-soluble beta-1,3-/beta-1,6-glucan heteropolymer characterized by Fleet and Manners (1976, 1977).

Horizontal gene transfer: regulated expression of a tobacco homologue of the Agrobacterium rhizogenes rolC gene

A tobacco homologue (trolC) of the rolC gene of the Agrobacterium rhizogenes Ri-plasmid was cloned and sequenced from Nicotiana tabacum L. cv. Havana 425. The coding region of trolC is similar in sequence (69-87% for DNA and 54-89% for the deduced amino acid sequence) to rolC genes of the agropine, mannopine, and mikimopine strains of Ri-plasmids and the N. glauca rolC homologue. Southern analyses showed that trolC is encoded by a small gene family derived from the tomentosiformis ancestor of tobacco. This suggests that trolC resulted from an ancient transfer of DNA between A. rhizogenes and a progenitor of modern tobacco. Transcripts of trolC were detected in three morphologically distinct cultivars of tobacco. trolC mRNA accumulated in young leaves and shoot tips, but not in lower leaves and roots of mature plants. Accumulation of trolC mRNA in cultured leaf tissues was strongly down-regulated by auxin and induced by cytokinin. These results are of particular interest because they suggest that a gene of bacterial origin introduced during evolution can have a function in a modern plant.

Cellobiohydrolase B, a second exo-cellobiohydrolase from the cellulolytic bacterium Cellulomonas fimi

The gene cbhB from the cellulolytic bacterium Cellulomonas fimi encodes a polypeptide of 1090 amino acids. Cellobiohydrolase B (CbhB) is 1037 amino acids long, with a calculated molecular mass of 109765 Da. The enzyme comprises five domains: an N-terminal catalytic domain of 643 amino acids, three fibronectin type III repeats of 97 amino acids each, and a C-terminal cellulose-binding domain of 104 amino acids. The catalytic domain belongs to family 48 of glycosyl hydrolases. CbhB has a very low activity on CM-cellulose. Viscometric analysis of CM-cellulose hydrolysis indicates that the enzyme is an exoglucanase. Cellobiose is the major product of hydrolysis of cellulose. In common with two other exoglycanases from C. fimi, CbhB has low but detectable endoglucanase activity. CbhB is the second exo-cellobiohydrolase found in C. fimi. Therefore, the cellulase system of C. fimi resembles those of fungi in comprising multiple endoglucanases and cellobiohydrolases.

The regulatory functions of the rolB and rolC genes of Agrobacterium rhizogenes are conserved in the homologous genes (Ngrol) of Nicotiana glauca in tobacco genetic tumors

To compare patterns of expression between the Ngrol genes of N. glauca and the Rirol genes of Agrobacterium rhizogenes, we performed fluorometric and histochemical analysis of transgenic genetic tumors on the hybrid of Nicotiana glauca x N. langsdorffii (F1) that harbored a beta-glucuronidase (GUS) reporter gene fused to the promoter of NgrolB, NgrolC, RirolB or RirolC. The promoters of NgrolB and NgrolC had 2- to 3-fold lower activity than those of RirolB and RirolC. However, the changes in patterns of GUS activity caused by deletion of NgrolB and NgrolC promoters were similar to those of RirolB and RirolC promoters. This result suggests that the cis-acting sequences that regulate the level of expression of RirolB and RirolC are conserved in the NgrolB and NgrolC promoters. Furthermore, an auxin dependent (NAA-dependent) increase in GUS activity was observed in the case of NgroB-GUS and RirolB-GUS. Histochemical analysis showed GUS activity encoded by both NgrolB-GUS and RirolB-GUS in normal-type F1 transgenic plants was located in meristematic zones, while that encoded by NgrolC-GUS and RirolC-GUS was detected mainly in vascular systems of various organs. Thus, the patterns of expression of the Ngrol genes were the same as those of the Rirol genes in terms of promotion by auxin and tissue-specificity, indicating that regulatory mechanisms for both sets of genes have been conserved during the evolution of the genus Nicotiana after transfer from a progenitor of Agrobacterium to that of Nicotiana.

Trehalose as a possible precursor of the sulfated L-galactan in the ascidian tunic

Among sulfated polysaccharides, those in the tunic of ascidians are unique: their major constituent sugar is galactose, which occurs exclusively in the L-enantiomeric form. Incorporation of D-[14C]glucose into tunic slices in vitro revealed that the cells epimerize D-glucose into L-galactose during biosynthesis of the sulfated polysaccharides. The interconversion of these two sugars involves exchange of hydrogen atoms at the epimerization sites with protons of the medium. Tunic cells also synthesize trehalose, although this disaccharide is not a prominent constituent of the tissue. Pulse-chase experiments using D-[14C]glucose reveal that incorporation of label into trehalose precedes the synthesis of the sulfated L-galactan. In addition, the loss of label from trehalose coincides with the appearance of label in the sulfated L-galactan. Based on these results, we speculate that trehalose in the ascidian tunic may be a precursor of the sulfated L-galactan.

Identification of the Agrobacterium tumefaciens C58 T-DNA genes e and f and their impact on crown gall tumour formation

DNA sequence analysis of the 4.4 kilobases (kb) Eco RI fragment 14 from T-DNA of Agrobacterium tumefaciens C58 revealed three open reading frames. One of them (945 bp) was supposed to encode the transcript e, the function of which has not been identified to date. Furthermore, a so far undescribed open reading frame (1035 bp) was identified, located in the centre of the Eco RI fragment 14 and termed gene f. The third open reading frame encoded the carboxy-terminal part of the agrocinopine synthase (Acs). The gene e-encoded protein showed significant homologies to the gene products of the Agrobacterium rhizogenes rolB gene and the Agrobacterium tumefaciens gene 5. Both gene products are supposed to regulate the plant's reaction on auxin. Depending on the plant species tested, Agrobacterium strains carrying mutations in gene e induced only small or almost no detectable crown gall tumours. According to these mutational studies and the protein homologies observed, the gene e product is suggested to be involved in tumour formation. Infection of several plant species with Agrobacterium carrying a mutated gene f, as well as expression of the gene f in transgenic tobacco plants did not lead to visible morphological changes. Therefore, in contrast to gene e, the gene f seems not to be essential for tumour formation. In order to study whether gene f is an active gene, its expression in agrobacteria and plants was monitored by translational lacZ fusion. In planta, the putative gene f-promoter mediates a tissue-specific expression pattern. Although gene f was expressed in free-living agrobacteria as well as in transgenic plants, the function of the f locus remained unclear. DNA homology studies with the f gene region revealed a mosaic-like DNA structure, indicating that this locus might be the result of genetic exchanges between different Agrobacterium strains during evolution.

The rolC promoter of Agrobacterium rhizogenes Ri plasmid is activated by sucrose in transgenic tobacco plants

The 5'-upstream region of the rolC gene of the Ri plasmid is expressed specifically in phloem cells of transgenic higher plants. In this study, we demonstrated that the rolC promoter is activated by sucrose in phloem cells of transgenic tobacco seedlings bearing rolC promoter-uidA chimeric fusion gene. Since the rolC promoter is not activated by sorbitol, sucrose metabolism rather than osmotic pressure exerted by the disaccharide may be responsible for induction. Thus, experiments using 5'-upstream deletion mutants, internal deletion mutants, and chimeric constructs with a heterologous promoter (-90 region of the cauliflower mosaic virus 35S promoter) were conducted to define the region of the rolC promoter involved in sucrose activation. The results indicated that a cis-acting sucrose responsive region of the rolC promoter is located between -135 and -94 bp with respect to the transcription initiation site. In phloem cells, high concentrations of sucrose are encountered owing to ongoing translocation of photosynthates from source to sink tissues. Therefore, sucrose as a signal molecule may regulate the phloem-specific expression of the rolC promoter.