FISH OF BACS WITH APOMIXIS SPECIFIC REGIONS ON CHROMOSOME COMPLEMENTS OF Paspalum simplex AND Boechera holboelli

¹ Wageningen University, Laboratory of Genetics, the Netherlands

² Institute of Plant Genetics IGV-CNR, Perugia, Italy

³ Wageningen University, Laboratory of Biochemistry, the Netherlands

⁴ IFREMER, La Tremblade & Max Planck Institute for Chemical Ecology, France

⁵ University of Perugia, Laboratory of Genetics, Italy

The warm-season grass Paspalum simplex from northern Argentina and Paraguay has both sexual diploid (2n=2x=20) and obligate apomictic polyploid forms (2n=4x=40). In backcross populations segregating for the apomixis trait we found a cosegregating SCAR marker, which we used for further selection of plasmids and BACs containing its DNA sequence. Fluorescence in situ Hybridization (FISH) of this BAC as probe on pachytene and metaphase I complements revealed a single clear signal in a distal euchromatin area of only one of the chromosomes, suggesting hemizygosity for the apomixis specific SCAR marker containing region and confirming monosomic inheritance of the dominant marker. The second apomixis model in this study is the Boechera holboellii/ drummondii complex, a close apomictic relative of Arabidopsis thaliana, in which both apomictic triploids (2n=3x=21) and 2x-aneuploids (2n=2x+1=15) and diploid sexuals (2n=2x=14) exist. We are focussing on a number of 2x-aneuploids lineages in which the extra chromosome is small and mainly heterochromatic, and so has characteristics of a B-chromosome. Molecular marker studies suggest that the B-chromosome contains apomixis specific alleles. This now is further tested in a number of FISH experiments using specific BACs from Arabidopsis on metaphase complements of Boechera. Five BACs from the chromosomes 3, 4 and 5 were selected on the basis of other studies in Paspalum, Poa, Medicago, Pennisetum and Boechera in which regions were suggested that may contain candidate genes or markers tightly linked to the apomixis trait. Tentative results for few of them did not yet show specific signals on the B chromosome, but revealed strong indications for structural karyotype heterozygosity for the apomictic Boechera genome.