Assessment of the efficiency of cotransformation of the T-DNA of disarmed binary vectors derived from Agrobacterium tumefaciens and the T-DNA of A. rhizogenes

Role of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase 1 in nodule development of soybean

Autoregulation of nodulation (AON) plays a central role in nodulation by inhibiting the formation of excess number of legume root nodules. In this study, the effect of hydroxymethylglutaryl-coenzyme A reductase 1 (GmHMGR1) gene expression on nodulation and the AON system in Glycine max (L.) Merr was investigated. Wild-type soybean (cultivar Bragg) and its near-isogenic supernodulating mutant (nitrate tolerant symbiotic) nts1007 were selected to identify the expression pattern of this gene in rootlets after inoculation by its microsymbiont Bradyrhizobium. For further analysis, the full length of GmHMGR1 and its promoter were cloned after amplification by inverse-PCR and BAC library screening. Also, we constructed an intron hairpin RNA interference (ihpRNAi) and a GmHMGR1 promoter: β-glucuronidase fusion constructs, consequently for suppression of GmHMGR1 and histochemical analysis in transgenic soybean hairy roots induced by Agrobacterium rhizogenes strain K599. The GmHMGR1 gene was functional during the early stages of nodulation with the AON system having a negative effect on GmHMGR1 expression and nodule formation in wild-type rootlets. GmHMGR1 was particularly expressed in the developing phloem within the root, nodules and nodule lenticels. Expression of GmHMGR1 in transgenic hairy roots was suppressed by RNAi silencing approximately 85% as compared to empty vector controls. This suggests that the GmHMGR1 gene has an important role in triggering nodule formation as its suppression caused a reduction of nodule formation in nts mutant lines with a deficient AON system.

Establishment of in vitro culture system for Codonopsis pilosula transgenic hairy roots

The aim of the study was to establish a reliable system of transgenic hairy roots in Codonopsis pilosula through Agrobacterium-mediated genetic transformation. For this, we optimized several steps in the process of A. rhizogenes strain C58C1 mediated hairy root induction, including the most appropriate medium, explant type, time for infection and co-cultivation. We achieved an induction rate of up to 100% when the roots of C. pilosula seedlings were used as explants, infected with A. rhizogenes C58C1 harboring pCAMBIA1305 for 5 min, followed by induction on 1/2MS supplemented with 0.2 mg/L naphthylacetic acid and 200 mg/L cefotaxime sodium. The co-transformed hairy roots were confirmed by PCR amplification of hygromycin phosphotransferase II gene and histochemical GUS assay, and the efficiency of transformation was 70% and 68.3%, respectively, when no hygromycin selection pressure was exerted. To increase biomass production, we excised and self-propagated the transformed hairy roots, which produce saponins. Our successful establishment of an in vitro culture system of transgenic hairy root for this species lays the foundation not only for assessing gene expression and function but also for obtaining high levels of secondary metabolites through genetic engineering technology.

Plant hairy root cultures as plasmodium modulators of the slime mold emergent computing substrate Physarum polycephalum

Roots of the medicinal plant Valeriana officinalis are well-studied for their various biological activities. We applied genetically transformed V. officinalis root biomass to exert control of Physarum polycephalum, an amoeba-based emergent computing substrate. The plasmodial stage of the P. polycephalum life cycle constitutes a single, multinucleate cell visible by unaided eye. The plasmodium modifies its network of oscillating protoplasm in response to spatial configurations of attractants and repellents, a behavior that is interpreted as biological computation. To program the computing behavior of P. polycephalum, a diverse and sustainable library of plasmodium modulators is required. Hairy roots produced by genetic transformation with Agrobacterium rhizogenes are a metabolically stable source of bioactive compounds. Adventitious roots were induced on in vitro V. officinalis plants following infection with A. rhizogenes. A single hairy root clone was selected for massive propagation and the biomass was characterized in P. polycephalum chemotaxis, maze-solving, and electrical activity assays. The Agrobacterium-derived roots of V. officinalis elicited a positive chemotactic response and augmented maze-solving behavior. In a simple plasmodium circuit, introduction of hairy root biomass stimulated the oscillation patterns of slime mold's surface electrical activity. We propose that manipulation of P. polycephalum with the plant root culture platform can be applied to the development of slime mold microfluidic devices as well as future models for engineering the plant rhizosphere.

RNAi-mediated down-regulation of ornithine decarboxylase (ODC) leads to reduced nicotine and increased anatabine levels in transgenic Nicotiana tabacum L

In leaf and root tissues of Nicotiana tabacum L. (common tobacco), nicotine is by far the predominant pyridine alkaloid, with anatabine representing only a minor component of the total alkaloid fraction. The pyrrolidine ring of nicotine is derived from the diamine putrescine, which can be synthesized either directly from ornithine via the action of ODC, or from arginine via a three enzymatic step process, initiated by ADC. Previous studies in this laboratory have shown that antisense-mediated down-regulation of ADC transcript levels has only a minor effect upon the alkaloid profile of transgenic N. tabacum. In the present study, RNAi methodology was used to down-regulate ODC transcript levels in N. tabacum, using both the Agrobacterium rhizogenes-derived hairy root culture system, and also disarmed Agrobacterium tumefaciens to generate intact transgenic plants. We observed a marked effect upon the alkaloid profile of transgenic tissues, with ODC transcript down-regulation leading to reduced nicotine and increased anatabine levels in both cultured hairy roots and intact greenhouse-grown plants. Treatment of ODC-RNAi hairy roots with low levels of the wound-associated hormone methyl jasmonate, or wounding of transgenic plants by removal of apices - both treatments which normally stimulate nicotine synthesis in tobacco - did not restore capacity for normal nicotine synthesis in transgenic tissue but did lead to markedly increased levels of anatabine. We conclude that the ODC mediated route to putrescine plays an important role in determining the normal nicotine:anatabine profile in N. tabacum and is essential in allowing N. tabacum to increase nicotine levels in response to wound-associated stress.

Development of a transgenic hairy root system in jute (Corchorus capsularis L.) with gusA reporter gene through Agrobacterium rhizogenes mediated co-transformation

Transgenic hairy root system is important in several recalcitrant plants, where Agrobacterium tumefaciens-mediated plant transformation and generation of transgenic plants are problematic. Jute (Corchorus spp.), the major fibre crop in Indian subcontinent, is one of those recalcitrant plants where in vitro tissue culture has provided a little success, and hence, Agrobacterium-mediated genetic transformation remains to be a challenging proposition in this crop. In the present work, a system of transgenic hairy roots in Corchorus capsularis L. has been developed through genetic transformation by Agrobacterium rhizogenes harbouring two plasmids, i.e. the natural Ri plasmid and a recombinant binary vector derived from the disarmed Ti plasmid of A. tumefaciens. Our findings indicate that the system is relatively easy to establish and reproducible. Molecular analysis of the independent lines of transgenic hairy roots revealed the transfer of relevant transgenes from both the T-DNA parts into the plant genome, indicating the co-transformation nature of the event. High level expression and activity of the gusA reporter gene advocate that the transgenic hairy root system, thus developed, could be applicable as gene expression system in general and for root functional genomics in particular. Furthermore, these transgenic hairy roots can be used in future as explants for plantlet regeneration to obtain stable transgenic jute plants.

The A622 gene in Nicotiana glauca (tree tobacco): evidence for a functional role in pyridine alkaloid synthesis

Nicotiana glauca (Argentinean tree tobacco) is atypical within the genus Nicotiana, accumulating predominantly anabasine rather than nicotine and/or nornicotine as the main component of its leaf pyridine alkaloid fraction. The current study examines the role of the A622 gene from N. glauca (NgA622) in alkaloid production and utilises an RNAi approach to down-regulate gene expression and diminish levels of A622 protein in transgenic tissues. Results indicate that RNAi-mediated reduction in A622 transcript levels markedly reduces the capacity of N. glauca to produce anabasine resulting in plants with scarcely any pyridine alkaloids in leaf tissues, even after damage to apical tissues. In addition, analysis of hairy roots containing the NgA622-RNAi construct shows a substantial reduction in both anabasine and nicotine levels within these tissues, even if stimulated with methyl jasmonate, indicating a role for the A622 enzyme in the synthesis of both alkaloids in roots of N. glauca. Feeding of Nicotinic Acid (NA) to hairy roots of N. glauca containing the NgA622-RNAi construct did not restore capacity for synthesis of anabasine or nicotine. Moreover, treatment of these hairy root lines with NA did not lead to an increase in anatabine levels, unlike controls. Together, these results strongly suggest that A622 is an integral component of the final enzyme complex responsible for biosynthesis of all three pyridine alkaloids in Nicotiana.

Large-scale plant micropropagation

Plant micropropagation is an efficient method of propagating disease-free, genetically uniform and massive amounts of plants in vitro. The micropropagation from cells can be achieved by direct organogenesis from hairy roots or regeneration via somatic tissue. Once the availability of embryogenic cell and hairy root systems based on liquid media has been demonstrated, the scale-up of the whole process should be established by an economically feasible technology for their large-scale production in appropriate bioreactors. It is necessary to design a suitable bioreactor configuration that can provide adequate mixing and mass transfer while minimizing the intensity of shear stress and hydrodynamic pressure. Automatic selection of embryogenic calli and regenerated plantlets using an image analysis procedure should be associated with the system. Using the above systems, it will be possible to establish an advanced plant micropropagation system in which the plantlets can be propagated without soil under optimal conditions controlled in plant factory. The aim of this review is to identify the problems related to large-scale plant micropropagation via somatic embryogenesis and hairy roots, and to summarize the most recent developments in bioreactor design. Emphasis is placed on micropropagation technology and computer-aided image analysis, including the successful results obtained in our laboratories.

Promoters of auxin-induced genes from tobacco can lead to auxin-inducible and root tip-specific expression

In previous studies we have identified several mRNAs which accumulate after addition of 2,4-dichlorophenoxyacetic-acid (2,4-D) to auxin-starved tobacco cells. The mRNAs corresponding to cDNA clone pCNT103 were found to accumulate transiently prior to the cell division response due to auxin treatment. In this study we determined the sequences of three 103-like cDNAs and two 103-like genes, GNT1 and GNT35. To further study the regulation of the expression of these genes their 5' regions were translationally fused with the beta-D-glucuronidase reporter gene (GUS). The GNT1 5' region led to GUS expression only in the root tips of transgenic plants. By using transgenic hairy-root cultures and transformed cell suspension cultures it was shown that the 5' regions of both GNT1 and GNT35 lead to 2,4-D-inducible expression of GUS activity. The homology of the 103-like genes with other auxin-regulated genes is evaluated.

Cotransformation and differential expression of introduced genes into potato (Solanum tuberosum L.) cv Bintje

The Dutch potato cultivar Bintje has been transformed by Agrobacterium strain LBA1060KG, which contains two plasmids carrying three different DNAs (TL- and TR-DNA on the Agrobacterium rhizogenes plasmid and TKG-DNA on the pBI121 plasmid). Several transformed root clones were obtained after transformation of leaf, stem, and tuber segments, and plants were then regenerated from these root clones. The expression of the various marker genes [rol, opine, β-glucuronidase (GUS), and neomycin phosphotransferase (NPTII)] was determined in several root clones and in regenerated plants. The selection of vigorously growing root clones was as efficient as selection for kanamycin resistance. In spite of the location of NPTII and GUS genes on the same T-DNA, 17% of the root clones did not show GUS activity. Nevertheless, Southern blot analysis showed that these root clones contained at least three copies of the GUS gene. Sixty-four per cent of the root clones contained opines. The expression of these genes, however, was negatively correlated with plant regeneration capacity and normal plant development. The differential expression of the marker genes in the transgenic potato tissues is discussed.

Over-expressing a yeast ornithine decarboxylase gene in transgenic roots of Nicotiana rustica can lead to enhanced nicotine accumulation

Transformed root cultures of Nicotiana rustica have been generated in which the gene from the yeast Saccharomyces cerevisiae coding for ornithine decarboxylase has been integrated. The gene, driven by the powerful CaMV35S promoter with an upstream duplicated enhancer sequence, shows constitutive expression throughout the growth cycle of some lines, as demonstrated by the analysis of mRNA and enzyme activity. The presence of the yeast gene and enhanced ornithine decarboxylase activity is associated with an enhanced capacity of cultures to accumulate both putrescine and the putrescine-derived alkaloid, nicotine. Even, however, with the very powerful promoter used in this work the magnitude of the changes seen is typically only in the order of 2-fold, suggesting that regulatory factors exist which limit the potential increase in metabolic flux caused by these manipulations. Nevertheless, it is demonstrated that flux through a pathway to a plant secondary product can be elevated by means of genetic manipulation.

Stable transfer and expression of chimeric genes in licorice (Glycyrrhiza uralensis) using an Ri plasmid binary vector

The pharmaceutically important plant, licorice (Glycyrrhiza uralenesis Fisher), was transformed with a binary vector system of an Ri plasmid, pRi15834, and a mini Ti vector, pGSGluc1, containing chimeric neo and gus genes. The transgenic state of transformed roots was confirmed by detection of agropine and mannopine and by Southern blot hybridization with T-DNA of pGSGluc1. One to three copies of T-DNA of pGSGluc1 was integrated into the genomic DNA of G. uralensis. The expression of chimeric neo and gus genes driven by TR 1' and 2' promoters, respectively, was demonstrated by enzymatic assays. Histochemical analysis showed that the chimeric TR2'-gus gene was expressed specifically in phloem and pericycle tissues of the transformed licorice roots.

A rapid screen for the detection of specific DNA sequences in plants

We have developed a simple and quick method ("wick blot") for detecting the presence of specific DNA sequences in plants, using radiolabeled DNA probes. The method requires only small amounts of tissue, about 15-25 mg. More than a hundred samples per day can be easily extracted and blotted. It works well on various species and tissues, including leaves, embryos, and callus. The method is ideally suited for screening large numbers of putative transformants, especially populations that have not been screened by prior selection.

Root hair protoplasts ofLotus corniculatus L. (birdsfoot trefoil) express their totipotency

Treatment of the roots of 24-48 h old seedlings of the forage legumeLotus corniculatus with 1.0% Cellulase YC, and 0.1% Pectolyase Y-23 in 4.2% mannitol solution released protoplasts from the tips of root hairs within 30-40 sec of enzyme incubation. Roots from approximately 1000 seedlings yielded 1.7×10(5) protoplasts. Ten percent of protoplasts divided to form cell colonies when cultured at 1.0×10(5) ml(-1) in droplets of KM8P medium with 0.6% Sea Plaque agarose. Colonies formed callus on UM agar medium; protoplast-derived tissues produced shoots on B5 medium containing 0.05 mg 1(-1) of BAP. Regenerated plants were phenotypically and cytologically normal (2n=2x=24±2), and produced nitrogen fixing root nodules following inoculation withRhizobium. These results confirm the totipotency of protoplasts isolated from specialised epidermal cells of seedling roots ofLotus corniculatus.

Expression and inheritance of inserted markers in binary vector carrying Agrobacterium rhizogenes-transformed potato (Solanum tuberosum L.)

Transgenic shoots were regenerated from eight diploid potato hairy root clones obtained by transformation with Agrobacterium rhizogenes harboring next to its wild-type Ri-plasmid a binary vector containing the neomycin phosphotransferase and the β-glucuronidase genes. The plants exhibited the typical hairy root phenotype. Of the plants isolated, 58% were tetraploid and 38% were diploid. Flowering and tuberization was much better in the diploid than in the tetraploid plants. Transgenic plants formed a significantly larger root system when grown on kanamycin-containing medium as compared to growth on kanamycin-free medium. Direct evidence for genetic transformation was obtained by opine, neomycin phosphotransferase and β-glucuronidase assays, and by molecular hybridization. Fourteen flowering diploid plants were reciprocally crossed with untransformed S. tuberosum plants, but only six were successful. Seedlings obtained from four crosses showed that all traits were transmitted to the offspring. Molecular analysis confirmed the presence of multiple integrations (copies) of both vector T-DNA and Ri-T-DNA. The genetic data, furthermore, suggest that the traits derived from Ri-T-DNA and binary vector T-DNA are linked, as no recombination between the different traits was observed.

Electroporation stimulates tranformation of freshly isolated cell suspension protoplasts ofSolanum dulcamara byAgrobacterium

Freshly isolated cell suspension protoplasts ofSolanum dulcamara were mixed withAgrobacterium rhizogenes, allowed to settle for 2 h, exposed to electrical pulses and further incubated for 2h. Two pulses of 600 V cm(-1) for 2 msec separated by 15 sec produced transformed colonies at relative and absolute transformation frequencies which were 3-4 and 10 fold greater than those obtained by co-cultivation of 3 days old protoplast-derived cells with bacteria. Transformed colonies were not produced when freshly isolated protoplasts were mixed withAgrobacterium but not electroporated. Biochemical analysis confirmed the transgenic nature of plants regenerated from protoplast-derived tissues.