High-efficiency <Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis>-mediated transformation of heat inducible sHSP18.2-GUS in <Emphasis Type="Italic">Nicotiana tabacum</Emphasis>

The chimerical gene, Arabidopsis thaliana sHSP18.2 promoter fused to E. coli gusA gene, was Agrobacterium rhizogenes-mediated transformed into Nicotiana tabacum as a heat-regulatable model, and the thermo-inducible expression of GUS activity in N. tabacum transgenic hairy roots was profiled. An activation of A. rhizogenes with acetosyringone (AS) before cocultured with tobacco's leaf disc strongly promoted transgenic hairy roots formation. Transgenic hairy roots formation efficiency of A. rhizogenes precultured with 200 μM AS supplementation was 3.1-fold and 7.5-fold, respectively, compared to the formation efficiency obtained with and without AS supplementation in coculture. Transgenic hairy roots transformed with different AS concentration exhibited a similar pattern of thermo-inducibility after 10 min to 3 h heat treatments detected by GUS expression. The peak of expressed GUS specific activity, 399,530 pmol MUG per mg total protein per min, of the transgenic hairy roots was observed at 48 h after 3 h of 42°C heat treatment, and the expressed GUS specific activity was 7–26 times more than that reported in A. thaliana, tobacco BY-2 cells and Nicotiana plumbaginifolia. Interference caused by AS supplementation on the growth of transgenic hairy roots, time-course of GUS expression and its expression level were not observed.     

In vitro analysis of susceptibility to Agrobacterium rhizogenes in 65 species of Mexican cacti

Susceptibility of Mexican cacti to Agrobacterium rhizogenes was evaluated in 65 species of 22 genera. Stem discs taken from in vitro cultured plants were inoculated with Agrobacterium rhizogenes A4 agropine-type strain that contains the wild RiA4 plasmid and the binary vector pESC4 with the nptII and gus genes. Hairy roots were produced directly from wounds, or starting from calli generated on the wounded surface, in 34 of the evaluated species. The frequency of hairy roots formation, the number of roots per explant and its growth rates were variable among the tested species. In the 31 remaining species the production of transformed roots was not observed under the conditions used in these experiments. Histochemical detection of β-glucuronidase (GUS) activity demonstrated the expression of this foreign gene in the hairy roots. PCR analyses demonstrated the presence of the rolB and nptII genes in the DNA of the transformed roots. The patterns of alkaloid-like compounds obtained by thin layer chromatography in some of the tested species were qualitatively similar between the transformed and non-transformed roots.     

The seasonal activity and the effect of mechanical bending and wounding on the PtCOMT promoter in Betula pendula Roth

In this study, 900-bp (signed as p including nucleotides –1 to –886) and partly deleted (signed as dp including nucleotides –1 to –414) COMT (caffeate/5-hydroxyferulate O-methyltransferase) promoters from Populus tremuloides Michx. were fused to the GUS reporter gene, and the tissue-specific expression patterns of the promoters were determined in Betula pendula Roth along the growing season, and as a response to mechanical bending and wounding. The main activity of the PtCOMTp- and PtCOMTdp-promoters, determined by the histochemical GUS assay, was found in the developing xylem of stems during the 8th–13th week and in the developing xylem of roots in the 13th week of the growing season. The GUS expression patterns did not differ among the xylem cell types. The PtCOMT promoter-induced GUS expression observed in phloem fibres suggests a need for PtCOMT expression and thus syringyl (S) lignin synthesis in fibre lignification. However, the PtCOMTdp-promoter induced GUS expression in stem trichomes, which may contribute to the biosynthesis of phenylpropanoid pathway-derived compounds other than lignin. Finally, a strong GUS expression was induced by the PtCOMT promoters in response to mechanical stem bending but not to wounding. The lack of major differences between the PtCOMTp- and PtCOMTdp-promoters suggests that the deleted promoter sequence (including nucleotides −415 to −886) did not contain a significant regulatory element contributing to the GUS expression in young B. pendula trees.     

Okadaic acid and trifluoperazine enhance <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation in eastern white pine

Mature zygotic embryos of recalcitrant Christmas tree species eastern white pine (Pinus strobus L.) were used as explants for Agrobacterium tumefaciens strain GV3101-mediated transformation using the uidA (β-Glucuronidase) gene as a reporter. Influence of the time of sonication and the concentrations of protein phosphatase inhibitor (okadaic acid) and kinase inhibitor (trifluoperazine) on Agrobacterium-mediated transformation have been evaluated. A high transformation frequency was obtained after embryos were sonicated for 45–50 s, or treated with 1.5–2.0 μM okadaic acid or treated with 100–200 μM trifluoperazine, respectively. Protein phosphatase and kinase inhibitors enhance Agrobacterium-mediated transformation in eastern white pine. A 2–3.5-fold higher rate of hygromycin-resistant callus was obtained with an addition of 2 μM okadaic acid or 150 μM trifluoperazine or sonicated embryos for 45 s. Stable integration of the uidA gene in the plant genome of eastern white pine was confirmed by polymerase chain reaction (PCR), Southern and northern blot analyses. These results demonstrated that a stable and enhanced transformation system has been established in eastern white pine and this system would provide an opportunity to transfer economically important genes into this Christmas tree species. Communicated by W. H. Wu     

Transformation through agroinfection on decapitated shoot apex of field-growing <Emphasis Type="Italic">Phyllanthus amarus</Emphasis>

A simple and easy transformation strategy was accomplished on field growing plants of Phyllanthus amarus, an anti-hepatitis B drug plant. Infection of Agrobacterium rhizogenes strains A₄M70GUS and ATCC 15834 on decapitated shoots of field growing P. amarus induced hairy roots and crown gall, respectively. Infection with A₄M70GUS yielded a mean of 23.2 roots from 40% plants in 40-day period. The crown gall induced on 30% plants after infection with ATCC 15834 grew to 5–10 mm in diameter. The roots and crown galls established in vitro on Murashige and Skoog (MS) basal medium grew well. The hairy roots yielded fivefold (6.91 g) biomass in half-strength MS liquid medium to that of the adventitious roots derived from internode explants in MS medium with 8.0 μM α-naphthaleneacetic acid (1.39 g). Histochemical assay and PCR analysis using the primers of uidA coding region confirmed the hairy roots induced by A₄M70GUS. The crown galls induced by ATCC 15834 were confirmed by PCR analysis using rolB gene primers. The protocol enables an easy and early accomplishment of hairy roots.     

Efficient production of Agrobacterium rhizogenes-transformed roots and composite plants for studying gene expression in coffee roots

The possibility of rapid validation and functional analysis of nematode resistance genes is a common objective for numerous species and particularly for woody species. In this aim, we developed an Agrobacterium rhizogenes-mediated transformation protocol for Coffea arabica enabling efficient and rapid regeneration of transformed roots from the hypocotyls of germinated zygotic embryos, and the subsequent production of composite plants. The A. rhizogenes strain A4RS proved to be the most virulent. High transformation efficiencies (70%) were obtained using a 2-week co-cultivation period at a temperature of 15–18°C. Using a p35S-gusA-int construct inserted in the pBIN19 binary plasmid, we could estimate that 35% of transformed roots were GUS positive (co-transformed). Using the GUS assay as visual marker, 40% composite plants bearing a branched co-transformed rootstock could be obtained after only 12 weeks without selection with herbicides or antibiotics. Transgenic coffee roots obtained with A. rhizogenes did not exhibit the ‘hairy’ disturbed phenotype and were morphologically similar to normal roots. PCR analyses demonstrated that all co-transformed roots were positive for the expected rolB and gusA genes. Transformed and non-transformed root systems from both susceptible and resistant varieties were inoculated with Meloidogyne exigua nematode individuals. Inoculation of composite plants from the Caturra susceptible variety resulted in the normal development of nematode larvae. Numbers of extracted nematodes demonstrated that transformed roots retain the resistance/sensibility phenotype of varieties from which they are derived. These results suggest that composite plants constitute a powerful tool for studying nematode resistance genes.     

Coculture of Pachyrhizus erosus (L.) hairy roots with Rhizobium spp.

Summary We have established an in vitro system for the induction and study of nodulation in Pachyrhizus erosus (jicama) via a hairy root-Rhizobium coculture. In vitro-grown P. erosus plantlets were infected with Agrobacterium rhizogenes (ATCC No. 15834) and two hairy root lines were established. Hairy roots were grown in a split-plate system in which compartment I (CI) contained MS medium with nitrogen and different sucrose levels (0–6%), while CII held MS medium without nitrogen and sucrose. Nodule-like structures developed in transformed roots grown in CI with 2–3% surcose, inoculated with Rhizobium sp. and transferred to CII. Nodule-like structures that developed from hairy roots lacked the rigid protective cover observed in nodules from plants grown in soil. Western blot analysis of nodules from hairy roots and untransformed roots (of greenhouse-grown jicama) showed expression of glutamine synthetase leghemoglobin and nodulins. Leghemoglobin was expressed at low levels in hairy root nodules.     

A rapid<Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated<Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> transient assay system

Stable transformation ofArabidopsis thaliana is a lengthy process that involves up to 3 mo of plant growth and seed selection. We have developed a rapid, 3-wk transient assay system to test the functionality ofcis-regulatory regions controlling expression of a reporter gene in plants before undertaking stable transformation. Two-week-oldArabidopsis seedlings were vacuum-infiltrated withAgrobacterium tumefaciens cultures carrying various upstream regulatory regions controllinguidA (β-glucuronidase [GUS]) expression. Seedlings were fixed and stained for GUS activity 3–5 d following infiltration. Regulatory regions tested in this system include the cauliflower mosaic virus (CaMV)35S promoter, the upstream regulatory region of ribosomal protein geneL23A-1, and a temperature-inducible regulatory region (HSP101B) also fromArabidopsis. The percentage of seedlings positive for GUS activity varied depending on the construct used, with the CaMV35S promoter producing the highest number of GUS-positive seedlings. Temperature induction treatments elicited increased GUS expression in seedlings transformed with theHSP101B regulatory region. Regardless of construct, GUS expression levels were higher in seedlings collected 5 d followingAgrobacterium infiltration than those collected 3–4 d postinfiltration.     

Recovery of phenotypically normal transgenic plants of Brassica oleracea upon Agrobacterium rhizogenes-mediated co-transformation and selection of transformed hairy roots by GUS assay

In this paper we describe the production of transgenic broccoli and cauliflower with normal phenotype using an Agrobacterium rhizogenes-mediated transformation system with efficient selection for transgenic hairy-roots. Hypocotyls were inoculated with Agrobacterium strain A4T harbouring the bacterial plasmid pRiA4 and a binary vector pMaspro::GUS whose T-DNA region carried the gus reporter gene. pRiA4 transfers T_L sequences carrying the rol genes that induce hairy root formation. Transgenic hairy-root production was increased in a difficult-to-transform cultivar by inclusion of 2,4-D in the medium used to resuspend the Agrobacterium prior to inoculation. Transgenic hairy roots could be selected from inoculated explants by screening root sections for GUS activity; this method eliminated the use of antibiotic resistance marker genes for selection. Transgenic hairy roots were produced from two cauliflower and four broccoli culivars. Shoots were regenerated from transgenic hairy root cultures of all four cultivars tested and successfully acclimatized to glasshouse conditions, although some plants had higher than diploid ploidy levels. Southern analysis confirmed the transgenic nature of these plants. T₀ plants from seven transgenic lines were crossed or selfed to produce viable seed. Genetic analysis of T₁ progeny confirmed the transmission of traits and revealed both independent and co-segregation of Ri T_L-DNA and vector T-DNA. GUS-positive phenotypically normal progeny free of T_L-DNA were identified in three transgenic lines out of the six tested representing all the cultivars regenerated including both cauliflower and broccoli.     

Nickel tolerance and hyperaccumulation in shoot cultures regenerated from hairy root cultures of <Emphasis Type="Italic">Alyssum murale</Emphasis> Waldst et Kit

Shoot cultures of nickel hyperaccumulating Alyssum murale were established from epicotyl explants of seedlings aseptically germinated on hormone-free MS medium. They were further maintained on media with 0–0.92 μM kinetin. Optimal shoot multiplication was at 0.46 μM kinetin. Inoculation by shoot wounding was performed with overnight suspension of A. rhizogenes A4M70GUS which contains GUS gene cointegrated in pRiA4. After 30 days hairy roots were produced at the wounding site in 31 explant (25% out of 124). Hairy roots were excised and further propagated on hormone-free medium as separate clones. In the first passage clones 3 and 6 could be distinguished by fast growth and spontaneous shoot regeneration. In other clones (12, 23 and 25) shoot regeneration required presence of cytokinins. The five shoot culture clones regenerated from hairy roots were further cultured on media with 0.46 μM kinetin. These shoots were characterized by good elongation and lateral shoot branching, short internodes, minute slightly curled leaves and well developed plagiotropic root system spreading over the surface of media. Thus all plants regenerated from hairy root cultures manifested the characteristic Ri syndrome phenotype. They all had a strong positive GUS reaction. PCR analysis confirmed presence of uidA sequence from the gus construct. They were also tolerant to nickel accumulating up to 24,700 μg g⁻¹ dry weight.     

Shoot regeneration capacity from roots and transgenic hairy roots of tomato cultivars and wild related species

The organogenetic competence of roots and Agrobacterium rhizogenes-induced hairy roots of twelve Lycopersicon genotypes was investigated. Both roots and hairy roots of L. peruvianum, L. chilense, L. hirsutum and two L. peruvianum-derived genotypes regenerated shoots after 2–4 weeks of incubation on zeatin-contained medium. Anatomical analysis showed that shoot regeneration in roots could be direct or indirect, depending on the genotype considered. Hairy roots showed considerable differences in their morphogenetic responses, when compared to the corresponding non-transgenic roots. The differences observed may reflect the influence of the introduced rol genes on hormonal metabolism/sensitivity. Hairy root-derived T0 plants had shortened internodes, wrinkled leaves and abundant root initiation, and most produced flowers and fruits with viable seeds. The hairy root syndrome was detected early in germinating T1 seedlings as a strong reduction in the hypocotyl length. Our data point to the possibility of the use of A. rhizogenes, combined with regenerating Lycopersicon genotypes, in a very simple protocol, based on genetic capacity instead of special procedures for regeneration, to produce transgenic tomato plants expressing rol genes, as well as, genes present in binary vectors. Furthermore, the regeneration differences observed in each Lycopersicon genotype and in transgenic materials expressing rol genes open the possibility for their use in the analysis of both the biochemical and the genetic background of organogenetic competence. This revised version was published online in June 2006 with corrections to the Cover Date.     

<Emphasis Type="Italic">Agrobacterium rhizogenes</Emphasis> mediated transformation of <Emphasis Type="Italic">Scutellaria baicalensis</Emphasis> and production of flavonoids in hairy roots

Using different explants of in vitro seed grown Scutellaria baicalensis Georgi plantlets, hairy roots were induced following inoculation of Agrobacterium rhizogenes strains A₄GUS, R1000 LBA 9402 and ATCC11325. The A₄GUS proved to be more competent than other strains and the highest transformation rates were observed in cotyledonary leaf explant (42.6 %). The transformed roots appeared after 15–20 d of incubation on hormone free Murashige and Skoog medium. Growth of hairy roots was assessed on the basis of total root elongation, lateral root density and biomass accumulation. Maximum growth rate was recorded in root:medium ratio 1:100 (m/v). Hairy root lines were further established in Gamborg B₅ medium and the biomass increase was maximum from 15 to 30 d. PCR, Southern hybridization and RT-PCR confirmed integration and expression of left and right termini-linked Ri T-DNA fragment of the Ri plasmid from A₄GUS into the genome of Scutellaria baicalensis hairy roots. GUS assay was also performed for further integration and expression. All the clones showed higher growth rate them non-transformed root and accumulated considerable amounts of the root-specific flavonoids. Baicalin content was 14.1–30.0 % of dry root mass which was significantly higher then that of control field grown roots (18 %). The wogonin content varies from 0.08 to 0.18 % among the hairy root clones which was also higher than in non-transformed roots (0.07 %).     

Agrobacterium tumefaciens-mediated transformation of Rhipsalidopsis gaertneri

A protocol for Agrobacterium tumefaciens-mediated genetic transformation of Rhipsalidopsis cv. CB5 was developed. Calluses derived from phylloclade explants and sub-cultured onto fresh callus induction medium over a period of 9–12 months were co-cultivated with A. tumefaciens LBA4404. Plasmid constructs carrying the nptII gene, as a selectable marker, and the reporter uidA gene were used. Transformed Rhipsalidopsis calluses with a vigorous growth phenotype were obtained by extended culture on media containing 600 mg l⁻¹ kanamycin. After 9 months of a stringent selection pressure, the removal of kanamycin from the final medium together with the culture of the transformed calluses under nutritional stress led to the formation of several transgenic adventitious shoots. Transformation was confirmed by GUS staining (for uidA gene), ELISA analysis and Southern blot hybridization (for the nptII gene). With this approach, a transformation efficiency of 22.7% was achieved. Overall results described in this study demonstrate that Agrobacterium-mediated transformation is a promising approach for this cactus species.     

Stable <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated genetic transformation of London plane tree (<Emphasis Type="Italic">Platanus acerifolia</Emphasis> Willd.)

London plane tree (Platanus acerifolia Willd.) is an important tree in urban landscaping but it suffers from a number of negative traits which genetic engineering could be used to address. As with many woody species, P. acerifolia has appeared recalcitrant to genetic transformation. However, the recent development of a method for regenerating shoots from P. acerifolia leaf explants suggests that such material could be a target for gene-transfer. Using an Agrobacterium tumefaciens strain in which the T-DNA carries the histochemically detected reporter gene β-glucuronidase (GUS), we have followed the transfer of genes from Agrobacterium to leaf explants of Platanus acerifolia. Using this system, we have identified a set of inoculation and co-cultivation conditions (notably: the pre-treatment of leaf explants with 0.4 M mannitol, an inoculation period of 10 min, a bacterial OD₆₀₀ of 0.8–1.0 and a co-cultivation period of 5 days) that permit a good frequency and reliability of transient gene-transfer. Optimum levels of antibiotics for bacterial elimination and kanamycin-resistant shoot regeneration were also established. By applying these parameters, we recovered eight independent stably transformed shoots that were kanamycin-resistant and contained the nptII T-DNA gene, as confirmed by PCR analysis. Furthermore, Southern blot analysis confirmed that, in at least five of these lines, the transgene was associated with high molecular weight DNA, so indicating integration into the plant genome.     

Transformation of sugar beet cell suspension cultures

Summary A sugar beet transformation method was developed using particle bombardment of short-term suspension cultures of a breeding line FC607. Highly embryogenic suspension cultures derived from leaf callus were bombarded with the uidA (gusA) reporter gene under the control of either the osmotin or proteinase inhibitor II gene promoter, and the npt II selectable marker gene. Transient uidA expression was visualized as 500–4000 blue units per 200 mg of bombarded cells 2 d after bombardment. Stably-transformed calluses were recovered on both kanamycin and paromomycin media. The greatest number of GUS (+) calluses was obtained when 50 or 100 mgl⁻¹ of kanamycin was applied 2 d after transformation for 3–5 wk, followed by either no selection or reduced levels of the antibiotic. PCR analyses of the GUS (+) callus lines revealed the expected size fragment for uidA and npt II genes. Stable incorporation of the uidA gene into the genome was confirmed by Southern blot analyses. Several transformed embryos were detected by histochemical β-glucuronidase (GUS) staining.     

Hairy root production in Arabidopsis thaliana: cotransformation with a promoter-trap vector results in complex T-DNA integration patterns

 In comparison with the production of transgenic plants, the generation of hairy roots has the advantage that more independent transgenic lines can be produced in a shorter period of time. Therefore, we wanted to combine this approach with the promoter-trapping strategy to identify nematode-induced plant promoters. For the efficient production and culture of transgenic hairy root lines of Arabidopsis thaliana, the standard Agrobacterium rhizogenes transformation procedure was modified to avoid rapid callusing of the hairy roots. An average of 0.72 independent kanamycin-resistant (Km^R) roots were obtained per leaf piece. However, a much lower frequency of reporter gene activation was obtained than expected from experiments with the same vectors in Agrobacterium tumefaciens: of more than 700 independent Km^R hairy roots tested, only 8 were β-glucuronidase (GUS) positive. DNA hybridization was done on ten hairy root lines, of which one had a single truncated T-DNA and the others multiple copies of T-DNA that led to complex hybridization patterns. In a parallel analysis of A. thaliana plants transformed with the same vectors using A. tumefaciens, relatively simple T-DNA integration patterns were obtained. The low occurrence of GUS-positive hairy root lines in our experiments could be explained by the multiple T-DNA copies, especially in inverted array, that result in high frequencies of gene inactivation. Received: 11 August 1998 / Revision received: 17 February 1999 / Accepted: 18 March 1999     

In vitro regeneration and Agrobacterium-mediated genetic transformation of Euonymus alatus

An in vitro plant regeneration method and an Agrobacterium tumefaciens-mediated genetic transformation protocol were developed for Euonymus alatus. More than 60% of cotyledon and 70% of hypocotyl sections from 10-day-old seedlings of E. alatus produced 2–4 shoots on woody plant medium (WPM) supplemented with 5.0 mg/l 6-benzylaminopurine (BA) plus 0.2 mg/l α-naphthalene acetic acid (NAA), and 77% of shoots produced roots on WPM medium with 0.3 mg/l NAA and 0.5 mg/l Indole-3-butyricacid (IBA). On infection with Agrobacterium tumefaciens strain EHA105 harboring a gusplus gene that contained a plant recognizable intron from the castor bean catalase gene to ensure plant-specific β-glucuronidase (GUS) expression, 16% of cotyledon and 15% of hypocotyl explants produced transgenic shoots using kanamycin as a selection agent, and 67% of these shoots rooted. Stable insertion of T-DNA into the host genome was determined with organ- and tissue-specific expression of the gusplus gene and further confirmed with a PCR-based molecular analysis.     

Assessment of conditions affecting <Emphasis Type="Italic">Agrobacterium</Emphasis> <Emphasis Type="Italic">rhizogenes</Emphasis>-mediated transformation of soybean

Agrobacterium rhizogenes-mediated transformation has become a powerful tool for studying gene function and root biology due to its quick and simple methodology. This transformation method is particularly suitable for those plants, including legumes, whose transformation using Agrobacterium tumefaciens has been challenging. Although there are some reports on A. rhizogenes-mediated transformation of legumes to produce ‘composite’ plants, conditions influencing A. rhizogenes-mediated transformation of soybean [Glycine max (L.) Merr.] have not been yet fully investigated. To better understand A. rhizogenes-mediated root transformation in soybean, we have evaluated the impact of genotype, plant age for infection, bacterial inoculating concentration, inoculation temperature, and other factors on transformation of soybean. The results have shown that there are significant differences among soybean genotypes in their susceptibility to A. rhizogenes. Soybean cv. Zigongdongdou is the most susceptible to A. rhizogenes strain K599 among 10 genotypes tested. The effects of seedling age have been evaluated, and 1-day-old plantlets are found to be optimal for hairy root induction. There are no significant differences in hairy root induction for bacterial suspension from OD₆₀₀ = 0.2 to OD₆₀₀ = 1.2. Under 16 h photoperiod, hairy roots can be induced both at 23°C/20°C and 28°C/25°C, but not at 33°C/30°C as day/night temperature regimes. Using this transformation protocol, almost 100% of the composite plants formed hairy roots within 2 weeks, and based on GUS histochemical analysis, 94.2% transformation frequency is obtained. Transgene integration has been also confirmed by Southern blot analysis. D. Cao and W. Hou contributed equally to this work.