Escherichia coli plasmid pBR313 insertion into plant protoplasts and into their nuclei

Historical account on gaining insights on the mechanism of crown gall tumorigenesis induced by Agrobacterium tumefaciens

The plant tumor disease known as crown gall was not called by that name until more recent times. Galls on plants were described by Malpighi (1679) who believed that these extraordinary growth are spontaneously produced. Agrobacterium was first isolated from tumors in 1897 by Fridiano Cavara in Napoli, Italy. After this bacterium was recognized to be the cause of crown gall disease, questions were raised on the mechanism by which it caused tumors on a variety of plants. Numerous very detailed studies led to the identification of Agrobacterium tumefaciens as the causal bacterium that cleverly transferred a genetic principle to plant host cells and integrated it into their chromosomes. Such studies have led to a variety of sophisticated mechanisms used by this organism to aid in its survival against competing microorganisms. Knowledge gained from these fundamental discoveries has opened many avenues for researchers to examine their primary organisms of study for similar mechanisms of pathogenesis in both plants and animals. These discoveries also advanced the genetic engineering of domesticated plants for improved food and fiber.

Gene transfer in cereals

Until recently, gene transfer in plants was achieved only by sexual hybridization. Now, in addition, plant genetic manipulation, with the use of both recombinant DNA and protoplast fusion technology, is being applied to an increasing range of plants. The soil bacterium Agrobacterium tumefaciens, with its associated plasmid, is used as a vector for introducing DNA into the genomes of dicotyledonous plants, but it has not proved suitable for cereals. Instead, the direct uptake of plasmid DNA into cereal protoplasts is being used for the transformation of cells in rice, wheat, and maize. Transformation efficiencies, in some cases, are becoming comparable to those obtained in dicotyledons with Agrobacterium. In rice it is now possible to regenerate efficiently whole plants from protoplasts, and this capability may soon be extended to the other cereals. By means of direct interaction of cereal protoplasts with plasmids, coupled with improved procedures for the regeneration of plants from their protoplasts, gene transfer in the cereals is becoming established at the frontiers of recombinant DNA technology.

Liposome-mediated introduction of the chloramphenicol acetyl transferase (CAT) gene and its expression in tobacco protoplasts

The expression plasmid vector pUC8CaMVCAT, containing the chloramphenicol acetyl transferase (CAT) gene, was encapsulated in large unilamellar vesicles (LUV) and introduced into tobacco protoplasts derived from either cell suspension culture or leaf mesophyll. Treatment with liposomes took place in a buffer containing either NaCl or CaCl2, but no polyethylene glycol. The presence of polylysine in the incubation buffer increased the adsorption of liposomes to protoplasts but decreased the efficiency of CAT gene expression.The expression of the introduced CAT gene could be monitored for at least seven days, following the treatment (about 25% acetylation at day 3 as well as at day 7). Plasmid DNA sequences could be detected, apparently unmodified, for at least nine days in the plant cells, though unintegrated in the host genome.

The permeability of electroporated cells and protoplasts of sugar beet

A simple method has been developed to determine the changes in permeability of protoplasts and intact cells when electroporated. Cells and protoplasts of sugar beet, Beta vulgaris L., were subjected to electric pulse treatments of different field strengths, pulse number and pulse duration, and the ability to accumulate and retain the hydrophilic dye phenosafranine was determined spectrophotometrically. Results of timecourse studies of phenosafranine accumulation and retention indicated that pores are formed or enlarged rapidly in the plasmamembrane and remain permeable to phenosafranine for relatively long periods; the half-life of the 'pores" was temperaturedependent. Both cells and protoplasts retained the highest levels of phenosafranine when supplied with a series of five rectangular pulses of 50 μs duration and of field strength 2500 V·cm(-1). If these parameters were exceeded, The phenosafranine content was reduced, concomitant with a decline in viability as indicated by fluorescein-diacetate staining, indicating the loss of the integrity of the plasmamembrane. The pattern of accumulation and retention by protoplasts of radioactivity from [(3)H]pABD1, a modified bacterial plasmid, was similar to that of phenosafranine, but uptake of the plasmid by cells was not demonstrated. The mothod can be used to determine conditions for the optimum permeabilization of protoplasts for direct gene transfer.

The biotechnology of Bacillus thuringiensis

One of the challenges in the application of biotechnology to pest control is the identification of agents found in nature which can be used effectively. Biotechnology offers the potential of developing pesticides based on such agents which will provide environmentally sound and economically feasible insect control alternatives. Such an agent, the insect pathogen Bacillus thuringiensis, is the subject of intense investigations in several laboratories. Insecticides which use the entomocidal properties of B. thuringiensis are currently produced and sold worldwide; new products are currently in the development stage. Herein, the biology and genetics of B. thuringiensis and the problems associated with current products are critically reviewed with respect to biotechnology. Moreover, the economic and regulatory implications of technologically advanced products are evaluated.

Rapid procedure for detection and isolation of large and small plasmids

Procedures are described for the detection and isolation of plasmids of various sizes (2.6 to 350 megadaltons) that are harbored in species of Agrobacterium, Rhizobium, Escherichia, Salmonella, Erwinia, Pseudomonas, and Xanthomonas. The method utilized the molecular characteristics of covalently closed circular deoxyribonucleic acid (DNA) that is released from cells under conditions that denature chromosomal DNA by using alkaline sodium dodecyl sulfate (pH 12.6) at elevated temperatures. Proteins and cell debris were removed by extraction with phenol-chloroform. Under these conditions chromosomal DNA concentrations were reduced or eliminated. The clarified extract was used directly for electrophoretic analysis. These procedures also permitted the selective isolation of plasmid DNA that can be used directly in nick translation, restriction endonuclease analysis, transformation, and DNA cloning experiments.

On procaryotic gene expression in eucaryotic systems

Numerous types of interaction between pro- and eucaryotes exist in nature, from the endosymbiosis of some bacteria with unicellular organisms and insects to the complex systems of bacterial flora associated with the skin and intestines of animals and man, and nitrogen-fixation and crown-gall tumor induction in plants. Until recently, such interactions were not thought to include genetic transfer, but an increasing body of evidence points to the probability of similar naturally-occurring exchanges with wide-ranging implications for evolution and genetic manipulation. Experiments to elucidate the possible effects of procaryotic genes in eucaryotic systems have included in vitro and in vivo studies with both plant and animal systems, for instance the translation of bacterial messenger RNAs in the wheat germ and rabbit reticulocyte systems and the introduction of bacterial genes into plant protoplasts, animal cells and whole organisms. In the present paper we have tried to summarize the results of experiments involving the uptake, replication, transcription, translation and integration of procaryotic genes in various eucaryotic systems and to discuss the implications of such findings for basic research as well as for possible biomedical applications. Awareness of the possibility of procaryotic-eucaryotic genetic interactions may help to elucidate unresolved questions in pathology, such as possible involvement of the intestinal flora in carcinogenesis, as well as to provide valuable probes of eucaryotic control mechanisms and new approaches in agricultural genetic engineering.

Variability of bacterial gene-directed enzyme production in human genetically deficient cells

Human beta-galactosidase-deficient skin fibroblasts from a patient with generalized gangliosidosis (GMI-gangliosidosis type I) were treated with phage lambda plac DNA, coding for Escherichia coli beta-galactosidase (beta-D-galactoside galactohydrolase, EC.3.2.1.23). New beta-galactosidase activity detected in cell extracts of phage DNA-treated GMI-gangliosidosis fibroblasts continued to vary considerably from one experiment to another. It behaved like the E. coli z-gene product upon immunochemical and physicochemical investigation. In some experiments the antigenic behavior of resultant beta-galactoside activity in lambda plac DNA-treated cells resembled that of mutant E. coli beta-galactosidase. Among the factors and variables that may be responsible for the variation in the results obtained here and elsewhere, low physical binding between prokaryotic mRNA sequences and fibroblast ribosomal RNA could play a part connected with effective translation. This hypothesis is discussed under the aspect of a comparison of the ribosomal binding site of lac z mRNA with the 3'-terminus of the eukaryotic 18s ribosomal RNA, which shows limited possibilities for base-pairing interactions. More extensive possibilities for forming Watson-Crick base pairs between their initiation site and the eukaryotic ribosomal binding site exist for other prokaryotic messengers, such as those of Q beta-replicase, f 1-coat protein, or UDPG-4-epimerase.