Molecular systematics, phylobiogeography and evolution of the genus Cardaminopsis HAYEK (Brassicaceae), the closest relatives of the model plant Arabidopsis thaliana (L.) HEYNH.

The genus Cardaminopsis belongs to the mustard family (Brassicaceae). This family includes not only commercially important crop plants such as the Brassicas, but also the most important dicotyledonous model for plant research Arabidopsis thaliana. Less than 10 years ago Cardaminopsis was integrated into a newly defined genus Arabidopsis. Consequently, evaluation of phylogenetic relationships within this newly circumscribed genus are of particluar interest. We are able to distinguish three major lineages (A. lyrata, A. arenosa, A. halleri) using DNA sequences of nuclear encoded regions distinct from A. thaliana. A few rare additional taxa might represent intermediate hybrids (e.g. A. croatica). In contast, maternally inherited molecular markers from the chloroplast genome are shared among various taxa and lineages. This can be explained either by past and recent hybridization, or by the existence of chloroplast haplotypes predating separation of the different taxa. The second hypothesis is confirmed by the finding that especially phylogenetically old haplotypes are shared between taxa and lineages. One of our major goals was the investigation of phylogeographic aspects - the distribution of genetic diversity in space and time. It is obvious that pleistocenic glaciation and deglaciation cycles had an enourmous impact on Arabidopsis evolutionary history. Interestingly, in former Cardaminopsis species classical refuge areas (Iberian Peninsula, Italy, or the Balkans) played only a minor role. Contrary, periglacial survival close to the glaciers or even on permafrost was the rule rather than the exception. This is demonstrated by a detailed analysis of more than 1500 individuals of A. arenosa and A. lyrata (including putative hybrids) in Lower Austria within a large suture zone between both species using molecular markers from the nuclear and plastidic genome. This periglacial hybridization scenario is confirmed by morphometric and cytological analysis. However, in summary we can conclude that hybridization and reticulation played only a minor role in Cardaminopsis/Arabidopsis evolution.