Chromosomal Evolution in Melampodium

Chromosome rearrangements are known to play an important role in the evolution of plant genomes. Changes in chromosome size and morphology are traceable by applying cytogenetic techniques, in particular in situ hybridization techniques, which allow mapping of individual families of DNA sequences or whole genomic parental DNA in plant chromosomes (fluorescence in situ hybridization - FISH, or genomic in situ hybridization - GISH, respectively). The potential of these methods for studies of plant evolution lies in the capability to trace subtle chromosomal rearrangements (e.g., translocations, inversions), which play an important role in differentiation, isolation, and eventual speciation, but are difficult to detect with classical karyological methods. Numerous examples of successful application of these methods exist for economically important plants or for model plants, e.g., Arabidopsis thaliana. Comparative evolutionary studies involving a wide comparisons among related species, however, are scarce. The genus Melampodium (Heliantheae, Asteraceae) provides a highly suitable system to study different modes of chromosomal changes and their contribution to plant evolution. The presence of different basic chromosome numbers in the genus connected via dysploidy (x = 9, 10, 11, and 12, and derived polyploid numbers) correlates well with taxonomic grouping, indicating that chromosome changes have played an important role in the evolution of the genus. The presence of auto- and allopolyploids, with explicit hypotheses on their origins, allows analysis of chromosomal evolution after polyploidization events. In the present study classical and molecular cytogenetic techniques will be used for the detailed analysis of chromosomal rearrangements during diversification of Melampodium. Several types of markers will be used, including both coding (rDNA) and non-coding (i.e., newly isolated types of species/genus-specific repetitive DNA) repetitive DNA. The main questions are (a) What was the basic ancestral chromosome number in Melampodium (b) Which mechanisms are involved in chromosome number change? (c) Which types of sequences are involved in chromosome structure/size changes? (d) What types of chromosome rearrangements accompany/follow auto- and allopolyploidization? The proposed research will contribute not only to a better understanding of one particular plant group, but will also provide more insights on the role and mechanisms of chromosomal change during plant evolution and speciation.