Hybrid Wheat

“We should always keep in mind the obvious fact that the production of seed is the chief end of the act of fertilization; and that this end can be gained by hermaphroditic plants with incomparably greater certainty by self-fertilization than by the union of the sexual elements belonging to two distinct flowers or plants.”

Charles Darwin (The effects of cross and self-fertilisation in the vegetable kingdom. Murray, London 1876.)

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Efforts in hybrid breeding have made this technology one of the main factors contributing to the substantial global rise in agricultural output over the last few decades. For hybrid breeding, an efficient pollination control system is necessary to avoid the unwanted self-pollination or sib-pollination of the female parental line. We try to develop a system that may will replace the chemical sterilization by a gametocide that is the conventional method used at present. The system is based on splitting a barnase gene, which causes male sterility by pollen ablation, into two fragments. Eventually, it allows growing the female partners as male-sterile plants, whereas the hybrid progeny resulting from the pollination by a pollinator line is fully fertile.
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THE "SPLIT GENE" APPROACH
A precursor-T-DNA (“provector”) containing two complementary tapetum-expressed barnase gene fragments controlled by a tapetum-specific promoter is transformed into plants. Site-specific deletions of the T-DNAs during plant development leads to two alternative derivative loci, with each producing only one of the two complementary Barnase precursor proteins. Crossing those plants that carry the respective complementary loci with each other leads to progeny that carry the two barnase gene fragments in allelic positions. These plants are male-sterile and are used as the female crossing partners for hybrid breeding. The hybrid progeny plants are fertile as the barnase fragments segregate completely in the F1. For the maintenance of the female crossing partner, the heterozygous plant can be crossed to a homozygous line. Given that the gene fragments conferring male sterility are linked to an herbicide tolerance gene, the heterozygous plants can be selected by applying an herbicide. In order to increase the stability of the barnase protein complex, barnase gene fragments have been fused to intein sequences that, upon translation, covalently fuse the Barnase fragments auto-catalytically in a process called protein-splicing.

Recombination Technologies

Site-specific recombination systems provide excellent tools for the controlled and precise manipulation of plant genomes. In plant biotechnology, the demand for specific and flexible molecular tools for genome modification is rapidly increasing. Our goal is to establish irreversible recombination systems that are feasible in commercial plants like wheat.

Moreover, we are interested in the molecular basis of homologous recombination in plants. Therefore, we are currently developing a novel high-throughput-assay system for the measurement of meiotic recombination in Arabidopsis thaliana.

Novel herbicide resistance systems

In the transgenic system, the male sterility gene should be linked to a herbicide resistance gene, thus allowing to maintain the male sterile parent as a heterozygote that, upon crossing to a wild type plant segregates fertile (herbicide sensitive) and sterile plants. Our research thus focuses on the development of applicable herbicide resistance systems for wheat and barley, including split-gene approaches and new versions of herbicide resistance genes.

Tissue culture techniques

In parallel to the establishment of molecular systems, wheat transformation technologies are a subject of interest. Plants are transformed via ballistic bombardment and through Agrobacterium-mediated transformation. New tissue culture approaches or the use of novel herbicide-systems (including split-genes) are under investigation.

Split transgene expression in wheat. In: Transgenic plants: protocoll and methods. Methods Mol Biol. Springer. In Press.

Method for determining meiotic recombination frequencies in plants (Patent , Appl.-No. EP10173968)

Systeme zur Kontrolle von Ausbreitungsfähigkeit und Aktivität pflanzlicher Transgene. GenomXpress 3

Streptomyces phiC31 integrase mediates site-specific recombination in wheat. Plant Cell Reports 27, 1821–1831.

High-yield production of authentic human growth hormone using a plant virus-based expression system. Plant Biotechnol. J. 3: 613-620.

In planta engineering of viral RNA replicons: efficient assembly by recombination of DNA modules delivered by Agrobacterium. Proc. Natl. Acad. Sci. USA 101(18): 6852-6857.

Silencing in Arabidopsis T-DNA transformants: The predominant role of a gene-specific RNA sensing mechanism versus position effects. Plant Cell 16(10): 2561-2572.

Patent: Processes of producing a plastid-targeted protein in plants. Application-No. DE20031021963 2003051.