Chromosome studies and genetic analysis of natural and synthetic apomictic model species

Some plants have gained the ability to produce seed without fertilisation. This alternative to sexual reproduction, known as apomixis occurs most frequently in species of the families of the grasses, roses and composites, and mostly in polyploids and is considered one of the ways to escape from hybrid sterility. An impressive number of apomictic mechanisms have so far been described; most of them with different developmental modes of embryo and endosperm. The trait is potential very promising for producing uniform seeds at high efficiency and low cost, and belongs therefore since long as one to the most wanted grails of the plant breeding community. This PhD thesis points at several fascinating genetical and chromosomal aspects of apomixis using the model species Arabidopsis thaliana and the apomicts of the closely related Boechera holboellii complex. Focus is on two different studies in apomixis research: 1) unravelling chromosome organisation and genomic composition of some of the natural diploid apomicts of Boechera and 2) genetic analysis of AtSERK 1 transformed Arabidopsis for engineering apomictic elements in this sexually propagating diploid.Boechera's unsurpassed suitability for research of natural apomicts is its impressive genomic plasticity, large geographical distribution and an endless source of different accessions. Quite exceptional is that apomixis also can occur at the diploid level. The chromosome study involving the two sexual diploid species, B. holboellii and B. stricta (2n=14), and six apomictic accessions of B. holboellii and B. X divaricarpa (2n=14 and 15) demonstrated obvious differences between the sexual and apomictic taxa. DAPI fluorescence and FISH with rDNA probes on mitotic cell spreads clearly uncovered two different aberrantchromosome, including a largely heterochromatic chromosome ( Het ) and one much smaller chromosome (Del). Moreover, striking variation between the assumed homologues and great differences between the chromosome po