Origin and evolution of apomixis in North American Boechera species, Brassicaceae

• Applicant: Professor Dr. Marcus Koch
• Subject Area: Evolution and Systematics of Plants and Fungi
• Term: from 2004 to 2008
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5437810

The American genus Boechera (formerly Arabis), Brassicaceae, froms a well-defined monophyletic taxon with 80 species centered in Western North America. Evolution of the genus is thought to have been driven by reticulation and apomixis. Latter trait is unique within the Brassicaceae and associated with exceptionally low ploidy levels (mostly diploid or triploid), which makes Boechera an ideal genetic study system. Furthermore, it has been shown that B chromosomes are associated with apomixis. Regarding evolution of the apomictic trait, DNA sequence data suggested Boechera stricta (= Arabis drummondii) as the origin of genome addition in aneuploid and triploid Boechera holboellii. The proposed project will mainly focus on the origin, transmission and taxonomic distribution of the apomictic trait and its consequences for the speciation and diversification of the genus. For this purpose, insights into evolutionary mechanisms gained during previous research efforts concentrating on three model species, sexual Boechera stricta (= Arabis drummondii), sexual and apomictic Boechera holboellii, and their hybrid Boechera divaricarpa, will be used as starting point. The aim of the proposed project is (i) to develop chloroplast and nuclear DNA based phylogenies of North American genus Boechera, in order to understand the distribution and modes of transmission, respectively, of polyploidy, apomixis and aneuploidy in a spatial and temporal context, (ii) to identifiy taxa, respectively, ancient genotypes involved in the consitution of species of hybrid origin, (iii) to show the taxonomic distribution of B chromosomes, and to verify, if they play universal role in the establishment of apomixis, (iv) to distinguish between monophyletic and polyphyletic origin of species, (v) to verify the importance of the Rocky Mountains as primary and the Sierra Nevada as secondary center of diversity on a genus wide level.

• DFG Programme: Research Grants
• Participating Person: Dr. Christoph Dobes