Inheritance of a Codon-Optimized Transgene Expressing Heat Stable (1,3-1,4)-β-Glucanase in Scutellum and Aleurone of Germinating Barley

Diter von Wettstein, Professor of Genetics and Master of Translating Science into Applications

The present and subsequent chapters in this volume are dedicated to the life and research of Professor Diter von Wettstein who contributed immensely to the development of science and education. His contributions spanned various fields of science such as genetics, physiology, ultrastructural analysis, molecular biology, genomics, and biotechnology including genome editing. He performed and promoted pioneering research in the fields of epigenetics, directed evolution of enzymes, synthetic biology (promoter and gene optimizations), and genomics (genome sequencing of baker's yeast). Glimpses of his time at the Carlsberg Laboratory and Washington State University, with examples from the research performed at these institutions, are included in this chapter. His life is an inspiration to the next generation of biologists. Despite difficult situations, his persistent efforts and keen desire to learn enabled him to overcome obstacles. He always tried to attain the best, excelling in translating fundamental knowledge into applications.

Transgenic barley: a prospective tool for biotechnology and agriculture

Barley (Hordeum vulgare L.) is one of the founder crops of agriculture, and today it is the fourth most important cereal grain worldwide. Barley is used as malt in brewing and distilling industry, as an additive for animal feed, and as a component of various food and bread for human consumption. Progress in stable genetic transformation of barley ensures a potential for improvement of its agronomic performance or use of barley in various biotechnological and industrial applications. Recently, barley grain has been successfully used in molecular farming as a promising bioreactor adapted for production of human therapeutic proteins or animal vaccines. In addition to development of reliable transformation technologies, an extensive amount of various barley genetic resources and tools such as sequence data, microarrays, genetic maps, and databases has been generated. Current status on barley transformation technologies including gene transfer techniques, targets, and progeny stabilization, recent trials for improvement of agricultural traits and performance of barley, especially in relation to increased biotic and abiotic stress tolerance, and potential use of barley grain as a protein production platform have been reviewed in this study. Overall, barley represents a promising tool for both agricultural and biotechnological transgenic approaches, and is considered an ancient but rediscovered crop as a model industrial platform for molecular farming.

Glycosylated F4 (K88) fimbrial adhesin FaeG expressed in barley endosperm induces ETEC-neutralizing antibodies in mice

The F4-positive enterotoxigenic Escherichia coli (ETEC) strains are a frequent cause of porcine post-weaning diarrhea. Orally administered F4 fimbriae or FaeG, the major subunit and adhesin of F4, induce a protective mucosal immune response in F4 receptor-positive piglets. Feed plants carrying immunogenic subunit proteins can offer great advantages for oral vaccination of domestic animals. Here, we describe high-level endosperm-specific production (1% of total soluble proteins) of FaeG in the crop plant barley. The endoplasmic reticulum-targeted recombinant endospermic FaeG (erFaeG) was shown to be heterogeneously glycosylated. The erFaeG showed resistance at digestive conditions simulating piglet gastric fluid. Glycosylation did not abolish the immunogenic character of the FaeG protein, since erFaeG was able to induce F4 fimbria-specific antibodies in mice. Biological activity of these anti-F4 antibodies was demonstrated in vitro by blocking the attachment of the F4+ ETEC to the F4 receptors present on porcine intestinal enterocytes.

From analysis of mutants to genetic engineering

This chapter describes the research of developing transgenic barley for synthesis of recombinant proteins with practical significance and of metabolic engineering of proanthocyanidin-free barley. The results were obtained by graduate students, postdoctoral researchers, and visiting scientists at the Carlsberg Laboratory from 1972-1996 and during the past ten years at Washington State University. It is written in appreciation of their enthusiasm, skill, and perseverance.

Genetically engineered stem rust resistance in barley using the Rpg1 gene

The stem-rust-susceptible barley cv. Golden Promise was transformed by Agrobacterium-mediated transformation of immature zygotic embryos with the Rpg1 genomic clone of cv. Morex containing a 520-bp 5' promoter region, 4,919-bp gene region, and 547-bp 3' nontranscribed sequence. Representatives of 42 transgenic barley lines obtained were characterized for their seedling infection response to pathotype Pgt-MCC of the stem rust fungus Puccinia graminis f. sp. tritici. Golden Promise was converted from a highly susceptible cultivar into a highly resistant one by transformation with the dominant Rpg1 gene. A single copy of the gene was sufficient to confer resistance against stem rust, and progenies from several transformants segregated in a 3:1 ratio for resistancesusceptibility as expected for Mendelian inheritance. These results unequivocally demonstrate that the DNA segment isolated by map-based cloning is the functional Rpg1 gene for stem rust, resistance. One of the remarkable aspects about the transformants is that they exhibit a higher level of resistance than the original sources of Rpg1 (cvs. Chevron and Peatland). In most cases, the Golden Promise transformants exhibited a highly resistant reaction where no visible sign of infection was evident. Hypersensitive necrotic "fleck" reactions were also observed, but less frequently. With both infection types, pathogen sporulation was prevented. Southern blot and RT-PCR analysis revealed that neither Rpg1 gene copy number nor expression levels could account for the increased resistance observed in Golden Promise transformants. Nevertheless, this research demonstrates that stem-rust-susceptible barley can be made resistant by transformation with the cloned Rpg1 gene.

T-DNA integration into the barley genome from single and double cassette vectors

Patterns and sites of T-DNA integrations into the barley genome from single and double cassette vectors are of interest for the identification of cultivars with value added properties as well as for the production of selection marker-free transgenic lines that can be retransformed. T-DNA/Plant DNA junctions were obtained by capturing a single-stranded DNA with a biotinylated primer annealing to the vector adjacent to the border and an adaptor ligated to a restriction site overhang in the flanking barley DNA. The captured junction was converted into a double strand and sequenced. Fifty left and right border junctions from plants transgenic for one of five human genes were analyzed. Primers of 15-30 nucleotides designed from the genomic DNA at the insertion site can PCR amplify fragments that identify unequivocally any transformant. Adjacent transgene insertions with single cassette vectors were always in tandem direct repeat configuration. With regard to T-DNA integration the patterns were comparable to the variations found in dicotyledonous plants. Twelve of the 46 integrations characterized by blast searches were within different regions of the BARE-1 retrotransposon element occurring with a frequency of 2 x 10(5) copies in the barley genome. The use of border junctions to identify number of copies and loci of integrates in transformants is discussed.

Improved barley broiler feed with transgenic malt containing heat-stable (1,3-1,4)-beta-glucanase

The low nutritional value of barley for poultry is because of the absence of an intestinal enzyme for efficient depolymerization of (1, 3-1,4)-beta-glucan, the major polysaccharide of the endosperm cell walls. This leads to high viscosity in the intestine, limited nutrient uptake, decreased growth rate, and unhygienic sticky droppings adhering to chickens and floors of the production cages. Consequently, the 7.5 billion broiler chickens produced annually in the United States are primarily raised on corn-soybean diets. Here we show that addition to normal barley of 6.2% transgenic malt containing a thermotolerant (1,3-1,4)-beta-glucanase (4.28 microg.g(-1) soluble protein) provides a weight gain equivalent to corn diets. The number of birds with adhering sticky droppings is drastically reduced. Intestines and excrements of chickens fed the barley control diet contained large amounts of soluble (1,3-1,4)-beta-glucan, which was reduced by 75 and 50%, respectively, by adding transgenic malt to the diet. The amount of active recombinant enzyme in the small intestine corresponded to that present in the feed, whereas an 11-fold concentration of the enzyme was observed in the ceca, and a 7.5-fold concentration occurred in the excrement. Glycosylation of the beta-glucanase isolated from the ceca testified to its origin from the transgenic barley. Analysis of the data from this trial demonstrates the possibility of introducing individual recombinant enzymes into various parts of the gastrointestinal tract of chickens with transgenic malt and thereby the possibility of evaluating their effect on the metabolism of a given ingredient targeted by the enzyme.

The production of recombinant proteins in transgenic barley grains

The grain of the self-pollinating diploid barley species offers two modes of producing recombinant enzymes or other proteins. One uses the promoters of genes with aleurone-specific expression during germination and the signal peptide code for export of the protein into the endosperm. The other uses promoters of the structural genes for storage proteins deposited in the developing endosperm. Production of a protein-engineered thermotolerant (1, 3-1, 4)-beta-glucanase with the D hordein gene (Hor3-1) promoter during endosperm development was analyzed in transgenic plants with four different constructs. High expression of the enzyme and its activity in the endosperm of the mature grain required codon optimization to a C+G content of 63% and synthesis as a precursor with a signal peptide for transport through the endoplasmic reticulum and targeting into the storage vacuoles. Synthesis of the recombinant enzyme in the aleurone of germinating transgenic grain with an alpha-amylase promoter and the code for the export signal peptide yielded approximately 1 microgram small middle dotmg(-1) soluble protein, whereas 54 microgram small middle dotmg(-1) soluble protein was produced on average in the maturing grain of 10 transgenic lines with the vector containing the gene for the (1, 3-1, 4)-beta-glucanase under the control of the Hor3-1 promoter.