Project

Discipline

biotechnology; apomixis; seed production; self-sustainable hybrid; cereals; genome editing; clonal reproduction

Lead
Apomixis ist eine Form der asexuellen Vermehrung von Pflanzen durch Samen, die in einigen hundert Arten vorkommt. Apomiktische Nachkommen sind genetisch identisch und enthalten ausschliesslich mütterliches Erbgut. Die Auslösung von Apomixis in landwirtschaftlich bedeutenden Nutzpflanzen ist das Fernziel des vorliegenden Projekts, da so die ertragreichen F1-Hybride genetisch fixiert und damit die Saatgutproduktion erheblich vereinfacht werden könnte.
Lay summary
Apomixis ist eine Form der asexuellen Vermehrung von Pflanzen durch Samen, die in einigen hundert Arten vorkommt. Apomiktische Nachkommen sind genetisch identisch und enthalten ausschliesslich mütterliches Erbgut. Die meisten natürliche Apomikten sind fakultativ, können sich also sowohl apomiktisch wie sexuell vermehren. Es ist deshalb wahrscheinlich, dass die beiden Fortpflanzungsmodi durch unterschiedliche Regulation derselben Gene zustande kommen. Die Auslösung von Apomixis in landwirtschaftlich bedeutenden Nutzpflanzen ist das Fernziel des vorliegenden Projekts, da so die ertragreichen F1-Hybride genetisch fixiert und damit die Saatgutproduktion erheblich vereinfacht werden könnte. Das Induzieren von Apomixis erfordert die Veränderung von drei Prozessen der Fortpflanzung: 1. Die Bildung einer Eizelle mit unverändertem, mütterlichem Erbgut; 2. die Auslösung der Embryonalentwicklung ohne Befruchtung; und 3. die Bildung funktionellen Endosperms. Wir haben in Mais zwei Mutanten identifiziert, welche die beiden ersten Schritte betreffen. Das für den 1. Schritt verantwortliche Gen haben wir zusammen mit einem Industriepartner molekular isoliert und zur Produktion der ersten klonalen Samen in Getreiden (Mais) genutzt. In diesem BRIDGE Discovery Projekt wollen wir das für den 2. Schritt verantwortliche Gen molekular isolieren und untersuchen, ob mithilfe dieser beiden Gene auch in anderen Getreiden Apomixis induziert werden kann, speziell im wichtigen Nahrungs- und Futtermittelgetreide Gerste. Sollte die in Mais entwickelte Technologie zur Produktion klonaler Samen auf andere Getreide übertragbar sein, so eröffnen sich damit ungeahnte Möglichkeiten für die Landwirtschaft, da Apomixis die Nutzpflanzenzucht und Saatgutproduktion revolutionieren könnte.

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Last update: 22.01.2020

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Communication	Title	Media	Place	Year

Harnessing apomixis in crop plants bears tremendous potential for plant breeding and seed production and has been viewed as the holy grail of agriculture. Apomixis, the asexual reproduction through seeds, occurs naturally in ~400 species but is not found in major crops. Apomixis results in the production of clonal seeds that inherit the entire chromosomal complement from the mother plant but lack a paternal contribution. Thus, apomixis preserves the genotype of the mother plant, resulting in clonal progeny, and can thus be used to fix complex genotypes over many generations. Due to their superior performance, F1 hybrids are preferred over inbred lines for agricultural use whenever possible. However, the heterosis effect is not maintained because traits segregate in the F2 generation and hybrid seeds have to be generated anew every year. If apomixis could be expressed in F1 hybrids, it would tremendously simplify breeding programs and seed production.Apomixis differs from sexual reproduction in three key steps: (i) avoidance of meiosis to maintain the maternal chromosome complement (apomeiosis), (ii) development of the unreduced egg cell into an embryo without fertilization (parthenogenesis), and (iii) functional endosperm formation. We have identified a maize mutant, non-reduction in female4 (nrf4) that produces nearly 100% unreduced egg cells, about 30% of which have no recombination and are thus apomeiotic. Nrf4 encodes a novel gene that specific to the grasses, which contain all major cereal crops, including rice, maize, wheat and barley. We have used nrf4 to generate the clones through seeds in any crop plant in 2016, demonstrating the feasibility of this approach. The University of Zurich and DuPont-Pioneer jointly filed a patent application to protect the use of Nrf4 to generate clones in cereals. We also recently isolated the parthenogenesis1 (par1) mutant in a large-scale genetic screen in maize, shown that the trait is heritable, and generated populations to molecularly clone Par1. The BRIDGE Discovery proposal will focus on the use of the Nrf4 and Par1 genes in cereals to induce apomixis in sexual crop plants and has three main objectives:1) Investigation of the transferability of Nrf4 to other crops, specifically barley2) Molecular isolation of the Par1 gene in maize3) Engineering of apomixis in barley, an important food and feed cropBeing able to induce apomixis in barley would be a first step towards a generalization of the approach using nrf4 and par1 mutants for the production of clonal progeny. It would have tremendous value for applications in agriculture, both in developed and developing countries. It is thus not surprising that both the agrobiotech industry and humanitarian institutions showed a strong interest in developing apomixis technology. However, the necessary long-term commitment required to tackle such a complex problem has hampered private-public partnerships in the past, such that most apomixis research was undertaked in public institutions and progress has been slow. At the end of the BRIDGE Discovery project, we will have shown that apomixis can be engineered in crop plants using mutations and that this approach is transferable to cereals in general. The use of mutations will allow the technology to be integrated into conventional breeding programs in addition to the biotechnological applications using transgenic approaches. The demonstration of the general usability of nrf4 and par1 to engineer apomixis in cereals will thus put us in a prime position to enter cooperations with seed companies or to raise financial support for a start-up company to commercialize the apomixis technology we developed.