High-frequency modification of plant genes using engineered zinc-finger nucleases

An efficient method for making directed DNA sequence modifications to plant genes (gene targeting) is at present lacking, thereby frustrating efforts to dissect plant gene function and engineer crop plants that better meet the world's burgeoning need for food, fibre and fuel. Zinc-finger nucleases (ZFNs)-enzymes engineered to create DNA double-strand breaks at specific loci-are potent stimulators of gene targeting; for example, they can be used to precisely modify engineered reporter genes in plants. Here we demonstrate high-frequency ZFN-stimulated gene targeting at endogenous plant genes, namely the tobacco acetolactate synthase genes (ALS SuRA and SuRB), for which specific mutations are known to confer resistance to imidazolinone and sulphonylurea herbicides. Herbicide-resistance mutations were introduced into SuR loci by ZFN-mediated gene targeting at frequencies exceeding 2% of transformed cells for mutations as far as 1.3 kilobases from the ZFN cleavage site. More than 40% of recombinant plants had modifications in multiple SuR alleles. The observed high frequency of gene targeting indicates that it is now possible to efficiently make targeted sequence changes in endogenous plant genes.

Rapid "open-source" engineering of customized zinc-finger nucleases for highly efficient gene modification

Custom-made zinc-finger nucleases (ZFNs) can induce targeted genome modifications with high efficiency in cell types including Drosophila, C. elegans, plants, and humans. A bottleneck in the application of ZFN technology has been the generation of highly specific engineered zinc-finger arrays. Here we describe OPEN (Oligomerized Pool ENgineering), a rapid, publicly available strategy for constructing multifinger arrays, which we show is more effective than the previously published modular assembly method. We used OPEN to construct 37 highly active ZFN pairs which induced targeted alterations with high efficiencies (1%-50%) at 11 different target sites located within three endogenous human genes (VEGF-A, HoxB13, and CFTR), an endogenous plant gene (tobacco SuRA), and a chromosomally integrated EGFP reporter gene. In summary, OPEN provides an "open-source" method for rapidly engineering highly active zinc-finger arrays, thereby enabling broader practice, development, and application of ZFN technology for biological research and gene therapy.

High-frequency homologous recombination in plants mediated by zinc-finger nucleases

Homologous recombination offers great promise for plant genome engineering. This promise has not been realized, however, because when DNA enters plant cells homologous recombination occurs infrequently and random integration predominates. Using a tobacco test system, we demonstrate that chromosome breaks created by zinc-finger nucleases greatly enhance the frequency of localized recombination. Homologous recombination was measured by restoring function to a defective GUS:NPTII reporter gene integrated at various chromosomal sites in 10 different transgenic tobacco lines. The reporter gene carried a recognition site for a zinc-finger nuclease, and protoplasts from each tobacco line were electroporated with both DNA encoding the nuclease and donor DNA to effect repair of the reporter. Homologous recombination occurred in more than 10% of the transformed protoplasts regardless of the reporter's chromosomal position. Approximately 20% of the GUS:NPTII reporter genes were repaired solely by homologous recombination, whereas the remainder had associated DNA insertions or deletions consistent with repair by both homologous recombination and non-homologous end joining. The DNA-binding domain encoded by zinc-finger nucleases can be engineered to recognize a variety of chromosomal target sequences. This flexibility, coupled with the enhancement in homologous recombination conferred by double-strand breaks, suggests that plant genome engineering through homologous recombination can now be reliably accomplished using zinc-finger nucleases.

Experimental data checker: better information for organic chemists

An experimental data checker has been developed that reads, analyses, and cross-correlates experimental information copied and pasted from authors' manuscripts, which will be useful for authors, referees, editors and readers of papers reporting new molecular information, and which makes possible a quantification of the accuracy of journals' data.

Growth performance of broilers using a phase-feeding approach with diets switched every other day from forty-two to sixty-three days of age

Phase-feeding (PF; Treatment 2) was tested relative to an NRC regimen (Treatment 1) to evaluate the impact of PF on broilers during the finisher period (42 to 63 d). Two modified PF treatments were also tested during this experiment: Treatment 3 involved lowering the amino acid requirements predicted with PF linear regression equations by 10% (PF10), Treatment 4 involved increasing the slope of the linear regression equations by 15% (PF15). Broilers fed Treatment 1 consumed a single diet throughout the experiment, whereas PF treatments were fed in a series of 11 diets in which feed was switched every other day, resulting in steadily decreasing lysine, SAA, and threonine levels. On Day 63, weight gain, feed intake, feed efficiency, and crude protein intake did not differ (P > 0.05) among birds fed PF treatments and Treatment 1. Digestible lysine and threonine intakes were increased (P < 0.05) for Treatment 1 relative to the PF treatments, and digestible SAA intake for the NRC treatment was increased (P < 0.05) relative to the PF10 and PF15 treatments. Compared to Treatment 1, no differences (P > 0.05) in percentage breast, wing, leg, or abdominal fat were observed when birds were fed PF, PF10, or PF15 diets. These results indicate that PF supports maximum growth performance during an extended finisher period, even when lysine, SAA, and threonine levels are reduced every other day. Economic analysis indicated that PF regimens may lead to savings ($ per kg weight gain or breast meat).

Identification of a Brazil-nut allergen in transgenic soybeans

BACKGROUND

The nutritional quality of soybeans (Glycine max) is compromised by a relative deficiency of methionine in the protein fraction of the seeds. To improve the nutritional quality, methionine-rich 2S albumin from the Brazil nut (Betholletia excelsa) has been introduced into transgenic soybeans. Since the Brazil nut is a known allergenic food, we assessed the allergenicity of the 2S albumin.

METHODS

The ability of proteins in transgenic and non-transgenic soybeans, Brazil nuts, and purified 2S albumin to bind to IgE in serum from subjects allergic to Brazil nuts was determined by radioallergosorbent tests (4 subjects) and sodium dodecyl sulfate-polyacrylamide-gel electrophoresis (9 subjects) with immunoblotting and autoradiography. Three subjects also underwent skin-prick testing with extracts of soybean, transgenic soybean, and Brazil nut.

RESULTS

On radioallergosorbent testing of pooled serum from four subjects allergic to Brazil nuts, protein extracts of transgenic soybean inhibited binding of IgE to Brazil-nut proteins. On immunoblotting, serum IgE from eight of nine subjects bound to purified 2S albumin from the Brazil nut and the transgenic soybean. On skin-prick testing, three subjects had positive reactions to extracts of Brazil nut and transgenic soybean and negative reactions to soybean extract.

CONCLUSIONS

The 2S albumin is probably a major Brazil-nut allergen, and the transgenic soybeans analyzed in this study contain this protein. Our study show that an allergen from a food known to be allergenic can be transferred into another food by genetic engineering.

Inhibition of gene expression in transformed plants by antisense RNA

We report the successful suppression of nopaline synthase (EC 1.5.1.19) enzymatic activity in the leaves of tobacco plants via the overproduction of RNAs complementary to the nopaline synthase (nos) mRNA. Several different regions of the nos gene were fused, in antisense orientation, to the promoter from a strongly expressed petunia chlorophyll a/b-binding protein gene. These constructions were directly introduced into a tobacco line which contained a single copy of the wild-type nos gene and transgenic plants were regenerated. The degree of nopaline synthase suppression in the leaves of the double transformants ranged up to 85% and was dependent on the particular region of the nos gene present in the antisense RNA. The most effective nos antisense sequences were derived from the 3' half of the nos gene transcript. In addition, we report a new sensitive method for the detection and quantitation of nopaline synthase activity in crude plant extracts.

Relative strengths of the 35S cauliflower mosaic virus, 1', 2', and nopaline synthase promoters in transformed tobacco sugarbeet and oilseed rape callus tissue

The 35S promoter of cauliflower mosaic virus and promoters from the nopaline synthase, 1' and 2' genes of Agrobacterium tumefaciens T-DNA were fused to the bacterial octopine synthase and chitinase gene coding regions. These chimaeric gene constructions were introduced into tobacco, sugarbeet and oilseed rape cells and their relative levels of expression measured by primer extension analysis of RNA isolated from pooled populations of stably transformed calli. In tobacco callus, the 35S promoter provided the highest levels of gene expression, followed by the 2', 1' and nopaline synthase promoters. While the ranking of these promoters is conserved in sugarbeet and oilseed rape callus, there is between-species variation in the relative strength of these promoters. In all three species, transcription initiation is conserved for each of the chimaeric gene constructions. Additional constructions in which the 5' untranslated leader of a petunia chlorophyll a/b binding protein gene is substituted for DNA downstream of the 35S transcription start site demonstrates that heterologous 5' leader sequences can be utilized to augment steady-state levels of reporter gene expression.

Psychiatric disorders in patients with cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis is a familial recessive disorder. Patients with the disorder present with tendon xanthomas, juvenile cataracts, dementia, and pyramidal and cerebellar abnormalities but have normal plasma cholesterol. High plasma cholestanol concentrations and abnormal bile acid metabolism are specific for this disease. The authors describe four patients with cerebrotendinous xanthomatosis and prominent psychiatric symptoms. In three of these patients appropriate diagnosis and treatment were delayed for years because the presence of cerebrotendinous xanthomatosis was not recognized. Early recognition of this potentially lethal disease is important because both the psychiatric and neurological symptoms respond to treatment with chenodeoxycholic acid.

A new procedure for increasing efficiency of protoplast plating and clone selection

Sea Prep(TM) agarose (FMC corp.) was used as a gelling agent for media in the culture of potato and tomato protoplasts. The concentration and conditions appropriate for gelling and liquifaction were determined. The new method provided increased calli transfer efficiency of up to 50-fold. Shoot formation from the protoplast-derived cells occurred normally and without reduction in frequency.