Agrobacterium-mediated transformation of pepino and regeneration of transgenic plants

Regeneration of pepino (Solanum muricatum Ait.) shoots was achieved both by organogenesis and by embryogenesis. Shoots derived via organogenesis were easily rooted and most regenerated plants appeared phenotypically normal. Transgenic plants were obtained using the binary vector pKIWI110 in the avirulent Agrobacterium tumefaciens strain LBA4404. Optimization of transformation protocols was rapidly achieved by monitoring early expression of the GUS (-D-glucuronidase) reporter gene carried on pKIWI110. Transgenic plants expressed GUS and selectable marker genes for kanamycin resistance and chlorsulfuron resistance. PCR (polymerase chain reaction) and Southern analysis provided molecular evidence for transformation.     

Regeneration of herbicide-tolerant black locust transgenic plants by SAAT

A protocol based on SAAT (sonication-assisted Agrobacterium-mediated transformation) has been developed to obtain herbicide-resistant transgenic black locust (Robinia pseudoacacia L.) plants. Cotyledon explants were co-cultivated with Agrobacterium AGL1 strain carrying the pTAB16 plasmid (bar and gusA genes). The effects of bacterial concentration (OD₅₅₀ of 0.3, 0.6, 0.8) and method of infection (sonication vs immersion) on bacterial delivery were determined by assaying cotyledons for transient -glucuronidase expression 3 days after infection. SAAT increases transient expression efficiency especially at an OD₅₅₀ of 0.6. After determining bacterial concentration and infection method, other factors affecting transformation efficiency, such as explant preconditioning and period of time before applying selection, were tested. From these experiments, the preferred protocol for black locust cotyledon transformation should include sonication of preconditioned cotyledons in AGL1 suspension, coculture for 3 days with 100 µM acetosyringone and transfer to selection medium with 4 mg/l phosphinothricin and 150 mg/l timentin. Of the initial explants, 2% produced at least one transgenic shoot. Genetic transformation was confirmed by Southern hybridization, chlorophenol red assay and herbicide tolerance of the regenerated plants.Abbreviations AS Acetosyringone - BA N-(Phenylmethyl)-1H-purin-6-amine (benzyladenine) - CR Chlorophenol red - 2,4-D 2,4-Dichlorophenoxyacetic acid - GUS -Glucuronidase - IAA Indole-3-acetic acid - IBA Indole-3-butyric acid - PPT PhosphinothricinCommunicated by P. Ozias-Akins     

Effective selection and regeneration of transgenic rice plants with mannose as selective agent

A new method for the selection of transgenic rice plants without the use of antibiotics or herbicides has been developed. The phosphomannose isomerase (PMI) gene from Escherichia coli has been cloned and consitutively expressed in japonica rice variety TP 309. The PMI gene was transferred to immature rice embryos by Agrobacterium-mediated transformation, which allowed the selection of transgenic plants with mannose as selective agent. The integration and expression of the transgene was confirmed by Southern and northern blot analysis and the activity of PMI indirectly proved with the chlorophenol red assay. The results of genetic analysis showed that the transgenes were segregated in a Mendelian fashion in the T₁ generation. The establishment of this selection system in rice provides an efficient way for producing transgenic plants without using antibiotics or herbicides with a transformation frequency of up to 41%.     

Generation of transgenic wheat plants producing high levels of the osmoprotectant proline

Plasmid DNA (pBI-P5CS), containing the selectable neomycin phosphotransferase-II `npt II' gene for kanamycin resistance and the reporter -glucuronidase `gus' gene as well as the Vigna aconitifolia ¹-pyrroline-5-carboxylate synthetase `P5CS' cDNA that encodes enzymes required for the biosynthesis of proline, was delivered into wheat plants using Agrobacterium-mediated gene transfer via indirect pollen system. Southern, northern and western blot analysis demonstrated that the foreign gene had been transferred, expressed and integrated into wheat chromosomal DNA. Salinity test indicated that proline acts as an osmoprotectant and its overproduction in transgenic wheat plants results in the increased tolerance to salt.     

Optimising the tissue culture conditions for high efficiency transformation of indica rice

Establishment of high efficiency Agrobacterium-mediated transformation techniques has greatly accelerated the widespread application of transformation in japonica rice. However, transformation in indica rice remains difficult. In this study, we identify two new media for subculture and differentiation, the two major steps in the tissue culture process for transformation. These media were tested using four cultivars representing very different germplasms of indica rice. The results show that the new media significantly improved the growth rate and quality of the calli, and also increased the differentiation rate for all four cultivars tested. Use of these modified media in transformation experiments also greatly improved the transformation efficiency of all four indica cultivars.     

A quick method to estimate the T-DNA copy number in transgenic plants at an early stage after transformation,using inverse PCR

Agrobacterium-mediated transformation of plants is known to result in transgenic plants with a variable number of integrated T-DNA copies [1, 2, 3, 7]. Our aim was to obtain transgenic tobacco plants containing one integrated T-DNA copy per genome. Therefore, a quick method was developed to estimate the T-DNA copy number of young transgenic plantlets within 10 weeks after transformation. Inverse polymerase chain reaction (IPCR) was used to amplify junction fragments, i.e. plant genomic DNA sequences flanking the known T-DNA sequences [5].     

The three-dimensional structure of theCyphomandra betacea chloroplast peripheral reticulum

Summary The peripheral reticulum (PR) inCyphomandra betacea chloroplasts originates as vesicles budding from the inner membrane of the chloroplast envelope which elongate to form tubules then aggregate or branch to form discrete PR units. Individual PR units of many coiled tubules may be connected with other units by narrow tubules. Serial sectioning revealed the discrete units to be approximately 650–1,000 nm wide, 400–500 nm high and 500–600 nm deep and to possess a compact morphology. TheCyphomandra PR structure is compared to the morphologies of chloroplast reticula reported for other plant species. A scheme to group PR from different species into 3 distinct morphological categories is outlined and discussed.     

Rapid,efficient production of homozygous transgenic tobacco plants withagrobacterium tumefaciens: A seed-to-seed protocol

An optimized complete protocol was developed forAgrobacterium tumefaciens-mediated transformation of tobacco (Nicotiana tabacum L. cultivar SR1), producing T₁ flowering plants homozygous for the inserted T-DNA as verified by kanamycin resistance in T₂ seedlings in 6 to 7 months from the time of cocultivation withAgrobacterium. Previous protocols require up to 9 to 12 months to obtain similar results. Procedures unique and important to this protocol include; a modified “whole-leaf” transformation coupled with a long duration of cocultivation, resulting in high rates of transformation, high levels of kanamycin in selection media resulting in few escapes, and extensive rooting of regenerants prior to a greenhouse hardening procedure. Once in the greenhouse, primary regenerants were maintained in small containers with long day photoperiod and high light levels, greatly shortening the time to seed set. Flowers from primary transformants were bagged to allow self pollination, and seed capsules harvested and dried prior to normal maturation on the plant. T₁ and T₂ seeds were plated and selected on kanamycin media by an improved seed plating technique which eliminates the need for the placement of individual seeds, saving time and improving selection homogeneity. Using this protocol, over 130 independent tobacco lines from six separate gene constructs have been generated in a very short time period. Of these 130, nearly 60 percent segregated 3∶1 for kanamycin resistance: susceptibility, indicating single transgene insertion events.     

Generation of transgenic Lolium temulentum plants by Agrobacterium tumefaciens-mediated transformation

Lolium temulentum L. (Darnel ryegrass) has been proposed to be used as a model species for functional genomics studies in forage and turf grasses, because it is a self-fertile, diploid species with a short life cycle and is closely related to other grasses. Embryogenic calluses were induced from mature embryos of a double haploid line developed through anther culture. The calluses were broken up into small pieces and used for Agrobacterium tumefaciens-mediated transformation. A. tumefaciens strain EHA105 harboring pCAMBIA1301 and pCAMBIA1305.2 vectors were used to infect embryogenic callus pieces. Hygromycin was used as a selection agent in stable transformation experiments. Hygromycin resistant calluses were obtained after 4–6 weeks of selection and transgenic plants were produced in 10–13 weeks after Agrobacterium-mediated transformation. Fertile plants were readily obtained after transferring the transgenics to the greenhouse. Transgenic nature of the regenerated plants was demonstrated by Polymerase chain reaction (PCR), Southern hybridization analysis, and GUS staining. Progeny analysis showed Mendelian inheritance of the transgenes. The transformation system provides a valuable tool for functionality tests of candidate genes in forage and turf grasses.     

Genetic transformation of Indian isolate of Lemna minor mediated by Agrobacterium tumefaciens and recovery of transgenic plants

Transgenic plants of an Indian isolate of Lemna minor have been developed for the first time using Agrobacterium tumefaciens and hard nodular cell masses ‘nodular calli’ developed on the BAP - pretreated daughter frond explants in B₅ medium containing sucrose (1.0 %) with 2,4-D (5.0 μM) and 2-iP (50.0 μM) or 2,4-D (50.0 μM) and TDZ (5.0 μM) under light conditions. These calli were co-cultured with A. tumefaciens strain EHA105 harboring a binary vector that contained genes for β-glucuronidase with intron and neomycin phosphortransferase. Transformed cells selected on kanamycin selection medium were regenerated into fronds whose transgenic nature was confirmed by histochemical assay for GUS activity, PCR analysis and Southern hybridization. The frequency of transformation obtained was 3.8 % and a period of 11–13 weeks was required from initiation of cultures from explants to fully grown transgenic fronds. The pretreatment of daughter fronds with BAP, use of non-ionic surfactant, presence of acetosyringone in co-cultivation medium, co-culture duration of 3 d and 16 h photoperiod during culture were found crucial for callus induction, frond regeneration and transformation of L. minor. This transformation system can be used for the production of pharmaceutically important protein and in bioremediation.     

Regeneration and genetic transformation of <Emphasis Type="Italic">Hagenia abyssinica</Emphasis> (Bruce) J.F. Gmel. (Rosaceae) with <Emphasis Type="Italic">rolB</Emphasis> gene

The effects of growth regulators, wounding and antibiotics on regeneration of Hagenia abyssinica were investigated and the rolB gene was introduced into this species by Agrobacterium-mediated transformation. Regeneration was affected by type of growth regulators, wounding and antibiotics. Up to 100% regeneration could be obtained. Three transformed clones (T1, T2.1, T2.2), confirmed by PCR and Southern blot, were obtained only by excluding kanamycin from the selection medium 6 weeks after culture, followed by selection during shoot multiplication. RT-PCR revealed strong expression of rolB gene in shoots and roots of all the transgenic clones, but from leaf samples, it was detected only in T1. Rooting frequency was 77% (T1), 50% (T2.1), 57% (T2.2) and 0% for control shoots on growth regulator-free rooting medium.     

Use of fused <Emphasis Type="Italic">gfp</Emphasis> and <Emphasis Type="Italic">gus</Emphasis> reporters for the recovery of transformed <Emphasis Type="Italic">Medicago truncatula</Emphasis> somatic embryos without selective pressure

We developed an alternative methodology for in vitro selection of transgenic Medicago truncatula cv. Jemalong plants using a bifunctional construct in which the coding sequences for the green fluorescent protein (GFP) and the β-glucuronidase protein (GUS) are fused. An Agrobacterium-mediated transformation protocol was used followed by regeneration via somatic embryogenesis in the dark, to avoid the synthesis and the consequent autofluorescence of chlorophyll. This method is a clear advantage over antibiotic and herbicide selection in which survival of non-transformed tissue is commonly reported, with the reassurance that all the somatic embryos selected as GFP positive are transformed. This was subsequently corroborated by the detection of GUS activity in leaves, stems and roots of the regenerated plants. Without antibiotic selection, and performing the embryo induction in the dark, it was possible to attest the advantage of using GFP as an in vivo detectable reporter for early embryo selection. The fusion with the GUS coding sequence provided additional evidence for the transformation of the previously selected embryos.     

Tissue culture and the use of transgenic plants to study plant development

Summary Recent advances in plant molecular biology have depended largely on the development of efficient methods of introducing foreign DNA into plant cells. Gene transfer into plant cells can be achieved by either direct uptake of DNA or the natural process of gene transfer carried out by the soil bacteriumAgrobacterium. Although both of these processes allow the generation of stably transformed plants, the former offers the advantage of allowing the study of transient expression of gene constructs in protoplasts cultured in vitro. In addition to the potential application of transgenic plants in agriculture and biotechnology they can be used to study the expression of foreign DNA, to carry out the functional analysis of plant DNA sequences, to investigate the mechanism of viral DNA replication and cell-to-cell spread, as well as to study transposition. Moreover, the versatility of the gene transfer vectors is such that they may be used to isolate genes unamenable to isolation using conventional protocols. Presented in the Formal Symposium Frontiers in Cell Biotechnology at the 41st Annual Meeting of the Tissue Culture Association, Houston, Texas, June 10–13, 1990.     

Green fluorescent protein as a vital marker for non-destructive detection of transformation events in transgenic plants

Transformation of plants is a popular tool for modifying various desirable traits. Marker genes, like those encoding for bacterial β-glucuronidase (GUS), firefly luciferase (LUC) or jellyfish green fluorescent protein (GFP) have been shown to be very useful for establishing of efficient transformation protocols. Due to favourable properties such as no need of exogenous substrates and easy visualization, GFP has been found to be superior in to other markers in many cases. However, the use of GFP fluorescence is associated with some obstacles, mostly related to the diminishing of green fluorescence in older tissues, variation in fluorescence levels among different tissues and organs, and occasional interference with other fluorescing compounds in plants. This paper briefly summarizes basic GFP properties and applications, and describes in more detail the contribution of GFP to the establishment, evaluation and improvement of transformation procedures for plants. Moreover, features and possible obstacles associated with monitoring GFP fluorescence are discussed.     

Polymerase chain reaction analysis of transgenic plants contaminated byAgrobacterium

Agrobacterium-mediated genetic transformation is a method of choice for the development of transgenic plants. The presence of latentAgrobacterium that multiplies in the plant tissue in spite of antibiotic application confounds the results obtained by polymerase chain reaction (PCR) analysis of putative transgenic plants. The presence ofAgrobacterium can be confirmed by amplification of eitherAgrobacterium chromosomal genes or genes present out of transfer DNA (T-DNA) in the binary vector. However, the transgenic nature ofAgrobacterium-contaminated transgenic plants cannot be confirmed by PCR. Here we report a simple protocol for PCR analysis ofAgrobacterium-contaminated transgenic plants. This protocol is based on denaturation and renaturation of DNA. The contaminating plasmid vector becomes double-stranded after renaturation and is cut by a restriction enzyme having site(s) within the PCR amplicon. As a result, amplification by PCR is not possible. The genomic DNA with a few copies of the transgene remains single-stranded and unaffected by the restriction enzyme, leading to amplification by PCR. This protocol has been successfully tested with 4 different binary vectors and 3Agrobacterium tumefaciens strains: EHA105, LBA4404, and GV3101.     

Details of T-DNA structural organization from a transgenic Petunia population exhibiting co-suppression

Analysis of Agrobacterium-transferred DNA (T-DNA) revealed strong correlations between transgene structures and floral pigmentation patterns from chalcone synthase (chs) co-suppression among 47 Petunia transformants. Presented here are the full details of T-DNA structural organization in that population. Sixteen transformants (34%) carried one T-DNA copy while 31 (66%) carried 106 complete and partial T-DNA elements in 54 linkage groups. Thirty linkage groups contained multiple T-DNA copies; 15 of these contained only contiguously repeated copies, 8 contained only dispersed copies and 7 contained both. Right-border inverted repeats were three times more frequent than left-border inverted or direct repeats. Large fragments of binary-vector sequences were linked to the T-DNA in seven plants.     

Manipulating photosynthesis

The levels of individual photosynthetic proteins can be independently decreased by theAgrobacterium-mediated transformation of plants with antisens RNA constructs. Protocols for the introduction of such constructs intoAgrobacterium, theAgrobacterium-mediated transformation of tobacco leaf disks, and the screening and analysis of the transgenic plants produced are described.     

Regeneration and transformation of Ribes

Transformation of the black currant cv. Ben More was achieved by utilising the binary vector system of Agrobacterium tumefaciens. This system involved the inoculation of peeled internodal stem segments with A. tumefaciens strain LBA4404 containing the binary vector PBI121.X with the marker genes Betaglucuronidase (GUS) and neomycin phosphotransferase II (NPTII). Shoot regeneration occurred on nutrient media based on M&S salts. Transformation was confirmed by the fluorogenic assay procedure which determined that the GUS gene had been transferred into the plant material and was being expressed. Concurrent transfer of the NPTII gene into the plant material was also confirmed with a dot blot assay on selected GUS positive plantlets.     

Rearrangements of large-insert T-DNAs in transgenic rice

Introduction of large-DNA fragments into cereals by Agrobacterium-mediated transformation is a useful technique for map-based cloning and molecular breeding. However, little is known about the organization and stability of large fragments of foreign DNA introduced into plant genomes. In this study, we produced transgenic rice plants by Agrobacterium-mediated transformation with a large-insert T-DNA containing a 92-kb region of the wheat genome. The structures of the T-DNA in four independent transgenic lines were visualized by fluorescence in situ hybridization on extended DNA fibers (fiber FISH). By using this cytogenetic technique, we showed that rearrangements of the large-insert T-DNA, involving duplication, deletion and insertion, had occurred in all four lines. Deletion of long stretches of the large-insert DNA was also observed in Agrobacterium.